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Monitoring & Forecasting - U.S.D.O.T. - 1980

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   This publication is part of a series entitled Transportation Planning
for Your Community and is designed to acquaint officials and planners
with transportation planning for communities of from 25,000 to 200,000

   The series consists of two guides that explain the concepts of trans-
portation planning and five technical manuals that describe techniques
for carrying out transportation planning programs.  The guides are: A
Guide for the Decisionmaker and The Manager's Guide for Developing a
Planning for the Decision Program.  The five technical manuals are

                            Traffic Planning

                            Transit Planning

                             System Planning

                       Monitoring and Forecasting

                          Programming Projects

   A Guide for the Decisionmaker describes the importance of urban
transportation and the benefits of transportation planning.  It includes
a review of how transportation planning works, and the role of city,
county and town officials in transportation planning.

   The Manager's Guide for Developing a Planning Program describes the
principles of transportation planning and is directed to those
engineers, planners and administrators who are charged with the
responsibility of organizing and administering the transportation
planning program.

   The individual technical manuals describe transportation planning
techniques appropriate for small communities.  The manuals also include
references to other publications that describe appropriate planning

   The Traffic Planning manual is a reference of basic traffic
engineering techniques and their potential for improving traffic flow
and traffic safety of urban arterial streets and highways.  The manual
identifies the traffic engineering measures appropriate for
consideration in development of transportation improvement plans and

   The Transit Planning manual includes techniques for estimating
transit patronage, service options, and operating requirements.  Also
included are procedures for evaluating the need for specialized services
for the elderly and handicapped.


              For sale by the Superintendent of Documents,
                     U.S. Government Printing Office
                         Washington, D.C. 20402

   The System Planning manual details the steps required for the
functional classification of streets and highways, the estimation of
future traffic, the estimation of the impacts of future traffic, and the
estimation of street and highway system requirements.  An Appendix
includes alternative methods for forecasting traffic.

   The Monitoring and Forecasting manual provides instructions for
assembling inventories of transportation and land activity.  It
describes methods for monitoring the performance of the transportation
system and general community development and methods for forecasting
information needed in urban transportation planning.

   The Programming Projects manual contains procedures for development
of the transportation improvement program.  Included are procedures for
identification of candidate improvement projects, determination of the
plan to fund candidate improvement projects, assignment-of priorities to
candidate improvement projects, budget allocation and project
scheduling, and monitoring, adjusting and evaluating the programs.

   This series was prepared by the COMSIS Corporation and the Highway
Users Federation for Safety and Mobility under a grant from the Federal
Highway Administration with the aid of a "steering committee" made up of
the following officials:

         Dan C. Dees
         Illinois Department of Transportation
         Springfield, Illinois

         James Echols
         Tidewater Transportation Commission
         Norfolk, Virginia

         David D. Grayson
         Automobile Club of Southern California
         Los Angeles, California

         John J. Holland
         Cumberland County Planning Board
         Bridgeton, New Jersey

         F.W. Landers
         Department of Public Works
         Worcester, Massachusetts

         Marion R. Poole
         North Carolina Department of Transportation
         Raleigh, North Carolina


   The principal investigators were:

         Arthur B. Sosslau
         COMSIS Corporation
         Wheaton, Maryland

         Marshall F. Reed, Jr.
         Highway Users Federation for Safety and Mobility
         Washington, D.C.

   Other principal authors were Maurice M. Carter of COMSIS Corporation
and Woodrow W. Rankin of the Highway Users Federation.


                            TABLE OF CONTENTS


PREFACE     . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

CHAPTER ONE: INVENTORIES. . . . . . . . . . . . . . . . . . . . . . . 3
   Street and Highway Inventory . . . . . . . . . . . . . . . . . . . 3
      System Mileage. . . . . . . . . . . . . . . . . . . . . . . . . 3
      Physical and Operating Characteristics. . . . . . . . . . . . . 4
      Travel Characteristics. . . . . . . . . . . . . . . . . . . . . 4
   Inventory of the Public Transportation System. . . . . . . . . . . 8
   Inventory of Land Activity . . . . . . . . . . . . . . . . . . . . 9
      Analysis Areas. . . . . . . . . . . . . . . . . . . . . . . . . 9
      Land Use Data . . . . . . . . . . . . . . . . . . . . . . . . .12
      Population and Household Characteristics. . . . . . . . . . . .12
      Employment Data . . . . . . . . . . . . . . . . . . . . . . . .14

CHAPTER TWO: MONITORING . . . . . . . . . . . . . . . . . . . . . . .18
   Establishing A Monitoring Program. . . . . . . . . . . . . . . . .18
      Monitoring for System Performance . . . . . . . . . . . . . . .18
      Monitoring to Update Inventory Information. . . . . . . . . . .20
      Scheduling of Data Items to be Monitored. . . . . . . . . . . .20
   Monitoring Travel Data . . . . . . . . . . . . . . . . . . . . .  22
      Roadway Data. . . . . . . . . . . . . . . . . . . . . . . . . .23
      Public Transportation Data. . . . . . . . . . . . . . . . . . .23
   Monitoring Changes in Land Activity. . . . . . . . . . . . . . . .26

CHAPTER THREE: FORECASTING. . . . . . . . . . . . . . . . . . . . . .29
   Population and Dwelling Unit Data. . . . . . . . . . . . . . . . .29
   Mean Household Income. . . . . . . . . . . . . . . . . . . . . .  30
      Phase I  Mean Income Estimation . . . . . . . . . . . . . . . .31
      Phase II  Distribution of Households by Income. . . . . . . . .31
   Auto Ownership . . . . . . . . . . . . . . . . . . . . . . . . . .31
   Employment . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

   REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . .34


                             LIST OF FIGURES

Figure Number                     Title                             Page

   1  Monitoring and Forecasting Procedure. . . . . . . . . . . . . . 2

   2  Potential Sources of Data..*..* . . . . . . . . . . . . . . . .19

   3  Typical Load Point Check Form . . . . . . . . . . . . . . . . .25

   4  Typical Transit Ride Check Form . . . . . . . . . . . . . . . .27

   5  Distribution of Households Based on Average
      Income Per Zone . . . . . . . . . . . . . . . . . . . . . . . .32

                             LIST OF TABLES

Table Number                      Title                             Page

   1  Number of Suggested Analysis Areas. . . . . . . . . . . . . . .10

   2  Sources of Land Use Data. . . . . . . . . . . . . . . . . . . .13

   3  Recommended Stratifications of Household
      Income. . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

   4  Employee Rates By Land Use Type . . . . . . . . . . . . . . . .16

   5  Suggested Monitoring Schedule for Communities
      Experiencing Moderate Growth. . . . . . . . . . . . . . . . . .21


   This manual describes procedures needed to forecast and monitor
transportation related characteristics.  Forecasting includes
estimations of future population, land-use and economic characteristics
for both the community and the traffic analysis zones within the
community.  Monitoring is an assessment of whether forecasts and
resultant travel demand estimates are achieved.

   A baseline inventory of existing conditions is important for both
forecasting and monitoring, and communities need to establish such an
inventory from which to launch a continuous transportation planning

   The transportation related characteristics that need to be forecast
are those that influence travel and that are required for transportation
system planning.  Other information needed for transportation planning
purposes other than for monitoring and forecasting are discussed in the
Traffic Planning, Transit Planning and Programming Projects manuals.

   The major purpose of monitoring is to determine if development trends
are evolving as forecast.  If major discrepancies between actual and
forecast change are found, the forecast transportation related
characteristics may need to be reviewed.  The monitoring program also
keeps the base inventory up-to-date.

   Initially, the following transportation related characteristics
necessary to evaluate whether development and travel demand trends agree
with forecasts should be monitored:

   -  Traffic Volumes
   -  Transit Patronage
   -  Dwelling Unit or Population Changes
   -  Changes in Total Employment
   -  Changes in the Transportation System (additions and/or deletions)

   In many situations, analyzing and projecting basic inventory items,
such as traffic volumes and transit patronage, will be sufficient to
identify problems and to plan improvements.  In communities where annual
travel and population growth rates are less than two percent, monitoring
should be limited to population and traffic, in addition to discussions
with elected officials, the public, and professionals in local area
departments (i.e., public works, police), to determine transportation

   It is recommended that monitoring in greater detail than discussed
above not be done unless the trends observed indicate a divergence from
anticipated trends or unless the basic data needs to be updated.  The
recommended updating is discussed in Chapter Two.

   Chapter One of this manual describes inventories required for
monitoring and forecasting.  Chapter Three discusses the forecasting
required for system planning.  The relationships between inventorying,
monitoring and forecasting, as related to system planning, is shown in
Figure 1.


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                                Figure 1


                               CHAPTER ONE


   Three types of inventories are recommended as the basis for
monitoring and forecasting.  These are:

         -  The street and highway system;
         -  The public transportation system
         -  Land use and socioeconomic characteristics,

   The street and highway system of an urban area is the focus of nearly
all travel, both by private automobile and public transportation.  The
inventory includes the functional classification of the system as well
as mileage, physical and operating characteristics and characteristics
related to the volume of traffic.

   Public transportation includes the municipal bus system, taxicab and
limousine service, local routes of interstate bus lines, school bus
operations, transportation for non emergency medical service, and
service for special programs such as the nutrition program for the

   Land use data are used for many purposes including transportation
planning.  Most urban area planning agencies will have land activity
data.  This information may need to be restructured for transportation
planning purposes.

   Socio-economic data is available through census tabulations and can
be augmented through local sources.  Auto ownership information may be
obtained from the motor vehicle administration.  Personal income data
exists in most State revenue office files.

   Inventory files describing land use and socioeconomic characteristics
of an urban area may be found in agencies such as the planning and
zoning office, employment security, tax assessor, State motor vehicle
administration and, of course, the State transportation agencies.  The
time spent seeking available data can save many man-hours in the
collection of new data.

                      STREET AND HIGHWAY INVENTORY

   The following three categories of data are required as part of the
street and highway inventory:

         -  System mileage;
         -  Physical and operating characteristics; and
         -  Travel characteristics.

System Mileage

   The first job is to establish the functional classification of the
street and highway system.  The functional classification process,
discussed in detail in the System Planning manual, classifies facilities
as follows:


            -  Major Arterials
            -  Minor Arterials
            -  Collector Streets
            -  Local-Access Streets

The first step of the street and highway inventory is to develop mileage
totals for each category of functional classification,

   The mileage of Major Arterial, Minor Arterial and Collector classes
is determined by measurement or from road inventory files.  Local-Access
street mileage is obtained by subtracting the total Arterial and
Collector mileage from the total street and highway mileage measured,
Freeway mileage should also be obtained as a separate category even
though it is classified as a
major arterial.

Physical and Operating Characteristics

   Each roadway segment should be identified to complete the basic
inventory.  Data, such as lighting , jurisdictional identification,
right-of-way width,, sidewalks, etc., can be appended to the records as
required.  Although not required for monitoring and forecasting, such
information is required as described in the Programming Projects manual.

   Knowledge of locations with high accident rates will assist in later
analyses.  It is recommended that an accident data system be established
to search out high accident locations, Major trouble spots should be
identified and can be plotted on a base map of the study area.

Travel Characteristics

   The first task of inventorying roadway volumes is to establish a
traffic counting program.  To begin, all roadways for which traffic
volumes are collected by other agencies can be eliminated from this
program.  The remaining roadway segments should be included in the
traffic counting program.  Traffic volumes should be posted on suitable
maps and included in the roadway segment inventory records.  Reference 1
provides guidelines on developing an integrated urban traffic counting

   Methods commonly used for counting traffic are: 1) using an automatic
traffic counter and 2) manually counting vehicles.2/ Automatic counters
are generally used for counting total volumes (either in one or both
directions).  Manual


counting is best suited for short counting periods or when it is
necessary to determine the volume of vehicles by vehicle type (e,g.,
cars light trucks, heavy trucks, etc,).  Generally, volumes from
automatic counters will satisfy the need in smaller urban areas,

   Automatic traffic counters may be borrowed from the State
transportation agency.  They record traffic volumes passing over a
pneumatic hose in a set time period.

   The State transportation agency may have permanent count locations in
the urban area.  Counts made for several years are useful for a study of
trends in traffic volumes.

   The time period for traffic counting is usually 1 hour, but equipment
is available for shorter time periods.  The analyst should be aware that
shorter time periods will increase the amount of data and tabulations
necessary to arrive at Average Daily Traffic (ADT) volumes.  The
counters assume one vehicle for every two actuations of the pneumatic
hose, If the road segment carries a large number of multi-axle trucks, a
correction should be made.  Without correction, accuracies of 95 percent
can be achieved.

   The objective of the counting program is to obtain an ADT volume of
the roadway segment.  In order to achieve the objective, it is
recommended that a minimum of one midweek 24-hour count be taken.  A 3-
day count will produce greater reliability.  For updating volumes, it is
recommended that one 24-hour count be taken at least every two years. 
Along each arterial, not roadway section, a 7-day count is recommended
each 2-years.  Below is an example of how to obtain an ADT volume for a
roadway segment:

   Given:   1. Three-day, 24-hour, weekday station counts of 8,465,
               9,100, 8,755 vehicles per day in October.

`           2. Seven-day average daily volume factor, relating weekday
               to average week of 0.986 (measured by State
               transportation agency for similar arterials).

            3. Month factor for October = .95 (areawide traffic volume
               factor from State transportation agency).

   Find:   ADT of roadway segment:

   STEP 1:  Average 24-hour volume from hose counts =

            8465 + 9100 + 8755
         --------------------------    = 8,773 vehicles per day,

   STEP 2:  ADT of roadway segment = observed travel x daily factor x
            monthly factor =  8,773 x .986 x .95
                           =  8,218 vehicles per day.


   Thus, in the above example, the roadway segment ADT volume is 8,218
vehicles per day.  The daily factor should be retained for future use
when updating the roadway segment volumes.

   For some planning purposes peak and off-peak period traffic volumes
may be required.  These can be calculated from traffic counter recorded
volumes.  Another approach would be to utilize hourly factors available
from other sources such as the State counting program.

   In addition to volume counts, it is also desirable to distinguish
between through traffic (traffic that uses the roadway system of the
study area but has neither a trip origin or trip destination within the
study area) and local traffic.  Observations suggest that through
traffic becomes a lower percentage of total traffic as the urban area
population increases. 3/  To distinguish between through and internal
travel, it will be necessary to conduct a limited roadside origin-
destination survey at the study area cordon.

   The roadside survey consists of stopping at least ten percent (20
percent is recommended) of all vehicles passing through the station for
driver interviews and a traffic count of all vehicles during the survey
period. 4,5/

   After selecting the external cordon stations, each site will require
a field reconnaissance to design a safe interviewing location.  The
location should be well signed for the motorists and designed tko
minimize traffic delays.  It is recommended that a law enforcement
agency assist in stopping traffic to be interviewed.  The public is more
responsive to a uniformed officer.

   One of the following two questions should be asked of each motorist:

   -  For trips entering the study area: "Where are you going?"

   -  For trips leaving the study area: "Where are you coming from?"

   If the place is inside the study area, the answer should identify the
actual address or the closest major intersection.  If the place is
outside the study area, it should identify the other cordon station
where the individual entered the study area.  Any additional questions
should be short, closed ended, and necessary for planning purposes. 
Trip purposes of frequency are examples.  Other data gathered, but not
asked should be the following:

      -  The number of people in the vehicle

      -  The vehicle type:
         -  passenger car/light truck, passenger
         -  light truck, commercial
         -  heavy truck


   Two products will evolve from the roadside interview when the data
are tabulated: (1)  the traffic volumes for the roadway segment at the
cordon, and (2)  a trip table for use with the system planning
procedures.  To obtain each, the following steps should be followed:

      STEP 1   -  For each station location, summarize the interviews by
                  vehicle type (and direction, if appropriate).

      STEP 2   -  Divide the total count (by vehicle type) by the number
                  of drivers interviewed to obtain the basic expansion

      STEP 3   -  Adjust the total counts for seasonal variation as
                  previously described.

      STEP 4   -  Code the geography of the trip origin and destination
                  for each trip surveyed.  These will be coded to an
                  external station or to a traffic analysis area within
                  the study area.

      STEP 5   -  Multiply each survey by the expansion and adjustment
                  factors to get the vehicle volume and vehicle trip
                  table for the station.

   If origin and destination information is not required for travel
across the cordon, the following simplified procedure based entirely on
traffic counts may be used.

      STEP 1   -  Draw the study area boundary on the map of roadway
                  facilities.  See System Planning manual, Chapter One.

      STEP 2   -  Place a traffic counting station at each point where
                  an arterial (including freeways) crosses the boundary.

      STEP 3   -  Following the counting procedure previously described,
                  inventory traffic at each of the locations.  Locations
                  where data are already being collected need not be
                  tabulated again.

   For more detailed information, consult the section on external travel
in the System Planning manual, Chapter Three and the Urban Origin-
Destination Surveys, Chapter Six. 6/



   An inventory of the public transportation system will include
services, equipment used in revenue service and fixed facilities.7/ The
inventory will consist of map files and tabulations.  A checklist of
requirements includes the following items:

   -  Map of Transit Routes by Type of Service (e.g., express, local)

   -  Map of Service Areas for Each Transit Operator (franchise, service

   -  Map of Actual Service Areas (areas actually served)

   -  Tabulation of Schedules, Service Periods, Service Levels and

   -  Tabulation of Equipment Used for Regular Passenger Service
      (revenue equipment)

   -  Tabulation  of Potential Revenue Equipment (vehicles used locally
      to serve selected public markets such as the elderly programs)

   -  Tabulation  of Fixed Facilities (passenger, maintenance and admini

   The transit routes for fixed-route service should be plotted on the
same scale base map as the roadway system.  Routes should be
distinguishable and should be categorized by service type - express
service, regular service and special service such as shopper specials.

   Using the base map and the route map, a series of overlays can be
prepared which, in total, can describe the complete physical public
transportation system.  To determine the actual service area for fixed-
route systems, a band 1/4 mile on either side of the route can be
constructed.  For demand responsive service, while a route is not
apparent, the service areas will describe the service zones.  These
overlays will be useful later when compiling statistics for monitoring

   Another overlay should describe the franchise service area.  The
franchise service area is the area in which the public transportation
system has the legal authority to operate.  All systems, whether public
or private, will have a franchise service area.  In towns and cities
where the franchise area is restricted,


the existing system coverage can be evaluated and compared to the
potential area of coverage.

   If the study area contains more than one public transportation
systems each system should be tabulated and mapped separately, The
systems considered should include taxicab operations and suppliers of
special services in addition to the bus operators.

   A companion to the service maps should be a tabulation of all routes,
Schedules and fare structures, by operating authority.

   If the operation is private, the public utilities commission or other
regulatory body will have complete files.  If the operation is public,
the analyst should look to the operator for information.  The analyst
also should be aware of private operators who are leasing vans or list
buses for ridesharing programs, which many communities have.

   All public vehicles used for passenger transportation in the study
area should be included in the inventory.  The word "public" includes
services for special classes of passengers such as vocational
rehabilitation program recipients.  Vehicles should be inventoried to
show the following data:

         -  Company or agency owned/leased

         -  Year of manufacture

         -  Model and manufacturer

         -  Seating capacity

         -  Special equipment (e.g., wheelchair lifts)

   Fixed facilities should be inventoried.  The amount of administrative
and maintenance space available will indicate the capacity for expanding
public transportation service.  The inventory should not carry through
to such items as bus stop signs and passenger waiting shelters.  If and
when this type of detail is needed, it can be inventoried.  The study
staff should produce only those data needed for the transportation
planning process.

                       INVENTORY OF LAND ACTIVITY

   Land activity information is a primary need in transportation
planning.  The trip generation element (see System Planning manual)
provides the linkage between land activity and travel.  Land activity
information for trip generation is usually described in terms of land
use intensity, character of the land use activities and location within
the urban environment.

Analysis Areas

   Prior to preparing a land activity inventory, a description of the
analysis areas is needed for applying the transportation planning
procedures.  'Guidelines for determining analysis areas are provided in
the System Planning manual.  Analysis areas provide the geographic units
for which transportation information is developed.  They are shown here
in Table 1.


                                 TABLE 1

                    Urban Area                Number of
                    Population             Analysis Areas

                      25,000                   10- 15

                      50,000                   20- 30

                      75,000                   30- 50

                     100,000                   35- 60

                     125,000                   45- 75

                     150,000                   55- 90

                     175,000                   65-100

                     200,000                   75-125


   One of the most useful data sources to the transportation planner is
the decennial census.  The U.S, Bureau of the Census publishes its data
by geographic area using both census tracts and enumeration districts. 
For a definition of tracts and enumeration districts refer to 1970
Census User's Guide.9/ Because census data are very useful, it is
recommended that the transportation analysis areas selected by the
transportation study group correspond to the census tract boundaries. 
The census tracts may be too large in many portions of the study area,
so the analyst may want to subdivide them when defining the
transportation analysis areas.  However, care should be taken that the
outer boundary of a group of analysis areas corresponds to the boundary
of a census tract.

   It is also desirable for the analysis areas to represent a specific
major type of land activity.  For example, an area may represent a
predominantly residential area, but other types of activity may also be
present, such as a neighborhood shopping or office complex.  The
following steps are recommended for charting the analysis areas:

      STEP 1   -  Using the base map, prepare an overlay showing the
                  geographic areas used for the decennial census -
                  census tracts and/or enumeration districts.

      STEP 2   -  In general terms prepare a land activity map of the
                  study area.  Categories of land activity should be
                  limited to;

                        -  Residential
                        -  Commercial
                        -  Industrial
                        -  Open Space

                  This  task can be accomplished by someone familiar
                  with the study area and need not be a definitive

      STEP 3   -  Overlay the roadway inventory onto the land activity
                  map.  It is desirable to subdivide analysis areas
                  along major roadway facilities, particularly freeways.

      STEP 4   -  Using the land activity map as a guide, subdivide or
                  aggregate the census boundaries to form the Traffic
                  Analysis areas.  Table I will guide the formulation of
                  the number of analysis areas.

   Once the boundaries are defined, the analyst is prepared to collect
demographic data for the small areas.  These analysis units will be used
in the transportation planning process through the evaluation of future
year scenarios.

   The following sections will describe land activity data in three

            1) type of land use

            2) number of residents

            3) number of employees


   For the base year, the analyst can obtain each of the data categories
with approximately the same level of effort, Future estimations of land
use data will probably require less effort than population and
employment data, Consequently, the analyst should be familiar with the
trip generation provisions of the System Planning manual, since the
areawide analytical procedures require residential and employment data,

Land Use Data

   The System Planning manual provides tripmaking characteristics for a
wide range of land use categories.  The analyst will need to decide the
degree of stratification desirable for the study area under
investigation.  However, the amount of data should be kept to a minimum. 
The land use categories required by the systems analysis procedures are,
by design, limited to data sufficient to determine retail and non-retail
employment for each analysis area.  Data on dwelling units are also

   Land use data is probably available locally from secondary sources. 
The only new data that may be required can be found through personal
observation of the analysis areas.  For inventory purposes, existing
land use data can be obtained from sources such as those show in Table
2.10/ Host urban areas have completed some form of land use study and
are beyond the need of this inventory.  In that event, the
transportation planning study group should secure the plan for future
use and organize the data by traffic analysis area.

Population and Household Characteristics

   Population and household characteristics should be inventoried in
tabular form, by traffic analysis area, for the base year.  The
tabulations should also be converted to a graphic presentation.  These
graphic presentations will aid the planner in analyzing the information.

   Secondary data available for the smaller urban areas preclude the
need to collect original population-related data.  Information should be
obtainable locally.  If not, it can be purchased from a commercial data
firm such as R.L. Polk.  The data required for transportation planning
are not extensive, but the analyst may wish to augment the basic data
with additional information on characteristics that can be used for
other analyses.  The basic data required to describe population and
household characteristics include:

            -  Dwelling units
            -  Income distribution
            -  Autos per household

   In addition to the basic data, other information is useful for
comparing inventories to data which will be monitored in future years to
assess changes.  These data need not be compiled at the traffic analysis
area level - it is sufficient if they are tabulated areawide.11/
Population composition by age group can be used to assess changes in
household size and changes in transportation system needs.  For example,
significant increases in the elderly population


                                 TABLE 2

                        SOURCES OF LAND USE DATA

     DATA SOURCE                             REMARKS

    Aerial Photography       Secondary source, excellent for verifying 
                             other information.

  U.S. Census (decennial     Primary source for housing; may
     & Special Census)       require disaggregation to traffic analysis

       Tax Assessor          Primary source for all land use types.

Planning and Zoning Agency   Primary source for monitoring.  can assist
                             with inventory if historical files are

Community Development Agency Primary source for recently redeveloped

    Chamber of Commerce      Secondary source, principally for
                             commercial and industrial data.


may indicate a need for increased public transportation.  Also, large
numbers of youths and students may not have access to an automobile and
may depend heavily upon public transportation..

   For the base year, provided it corresponds to a decennial census or
special five year census, dwelling unit data are available by census
geography.  In those areas with over 50,000 population, data are
available at the block level and can be aggregated to the traffic
analysis areas of the study area.  Of course, population data are
available from the same source and can be tabulated at the same time.9/

   Household income data are also available from the census population
reports.  The inventory may preserve the income distribution shown in
the System Planning manual's trip generation tables.  In forecasting
income the classifications may be reduced, especially if other trip
generation tables are to be utilized.  As with much of the data, the
number of strata is dependent upon local needs.  In urban areas with
overall growth of less than two percent per year, data should be
compressed as much as possible.  A suggested income classification based
on 1979 incomes is shown in Table 3.

   Income data maybe available from local sources such as the State
revenue agency.  The agency in each State has a file of personal income
for tire preceding year that can be summarized by analysis area to yield
the number of households within each income stratum.  Since the files
are generally confidential, procedures must be worked out with the State
revenue office to ensure the protection of privacy.  Obtaining income
information in this manner should be carefully assessed to determine if
it is cost-effective.

   Data on autos per household are available from the census
tabulations.  If census data are used for tabulating other household
characteristics, the same source should also be used for auto ownership

   Auto ownership data may be obtained through State motor vehicle
registration files.  It is recommended that the transportation analyst
develop a control total from autos registered, even if census data is
used, for comparison.  The auto registration files, like income data
from the State revenue office, will require address coding to the
appropriate traffic analysis zone and aggregation, by household, to get
the range of households by auto ownership.  Again, obtaining auto
ownership data in this manner should be carefully assessed to determine
if it is cost-effective.

Employment Data

   Employment data are difficult to secure, For system planning
purposes, it is only necessary to stratify employment into two groups:
retail and non-retail employment.  Even so, the inventory may require
considerable effort if an employment file does not currently exist.

   Because of the effort, the analyst will want to consider converting
land use data to employment by applying employee rates per acre or gross
floor area (GFA).  Such information is available from trip generation
studies made for major trip generators by many States and metropolitan
planning organizations.  Table 4


                                 TABLE 3
                            HOUSEHOLD INCOME

      STRATA                      HOUSEHOLD INCOME RANGE
         1                                $0 -   5,000
         2                            $5,000 -   7,999
         3                            $8,000 -   9,999
         4                           $10,000 -  14,999
         5                           $15,000 -  19,999
         6                           $20,000 -  24,999
         7                           $25,000 -  34,999
         8                           $35,000 -  49,999
         9                           $50,000 +        


                                 TABLE 4

                     EMPLOYEE RATES BY LAND USE TYPE

      GENERATOR                        EMPLOYEES PER

                          1000 sq. ft. GFA               Acre


  Free Standing
     Discount Store              0.9
     Discount Store with
        Super Market             2.7
     Department Store            1.1                     27.4

  Shopping Center

     Regional (over 1 million
        sq. ft.)                 1.1                     18.8
     Community (100,000-500,000
        sq. ft.)                 1.7                     18.1


  Free Standing

     General manufacturing       1.8                     17.6
     Warehouse                   1.2                     15.3
     Research/Development        2.1                     25.3
     Industrial Park             2.3                     18.4
     General Light Industry      1.7                     16.4
     All Industry Average        1.8                     20.0


  General                        3.3                     21.4
  Medical                        2.5                     17.0
  Governmental                   4.0                      5.5
  Engineering                    6.6                     80.6
  Civic Center                   4.1                      5.4
  Office Park                    6.4                     83.9
  Research Center                3.0                     11.9


  County Park                                             0.2


  All Categories                                          6.6

Source: National Cooperative Highway Research Program, Report 187:
        Quick Response Urban Travel Estimation Techniques and
        Transferable Parameters,User's Guide, (Washington, D.C.,
        Transportation Research Board, 1978).


is an example from information in Quick Response Urban Travel Estimation
Techniques and Transferable Parameters, User's Guide.12/

   Retail employment is associated with commercial sales.  It includes
department stores, supermarkets, specialty shops, etc.  Non-retail
employment includes the following categories:

         -  Government
         -  Office
         -  Financial, Insurance & Real Estate
         -  Industrial
         -  Manufacturing

   Other local sources the analyst may use to create an employment base
file include the offices of employment security, the community or State
planning office and the Chamber of Commerce.  Also, the Bureau of the
Census provides useful tabulations.9/  If the population and dwelling
unit data were derived from census information, the analyst will want to
verify employment rates between the sources in order to resolve
discrepancies and avoid gaps in the employment data file.


                               CHAPTER TWO

   Monitoring is an important planning function that should be
considered as two activities.  The first is gathering sufficient data to
assess the trends of development and travel.  The trends will show if
the transportation system is performing as anticipated and will help
identify potential problems.  The second is keeping current the basic
transportation information needed for system planning.  The following
major categories of information should be considered in monitoring:

         -  Change in Land Use,Population, Dwelling Units and Auto
         -  Change in Employment
         -  Change in Vehicle Miles of Travel
         -  Change in Transit Patronage
         -  Changes in Transportation System Service and Operation


   Monitoring should be considered as a continuing activity.  The
transportation study team should discuss individual participation and
agree on a monitoring program.  Liaison should be established with
agencies which can supply information to the transportation study.  A
list of agencies which may contribute to the monitoring program are
shown in Figure 2. Specific needs should be discussed with the State
revenue office and other such agencies to secure their cooperation.  The
monitoring program should be formally established to inform each agency
and individual about what is required of them and when.

   Monitoring activities will vary by urban area size and growth rate. 
Stable urban areas probably need to monitor activities only for the area
as a whole.  Monitoring by separate traffic analysis areas is worthwhile
only when major changes occur or when the growth rate is greater than
two percent per year.

   The following sections describe monitoring activities as they would
occur in a fast growing urban area.  Depending upon the characteristics
of the urban area, the monitoring activities may not have to be

Monitoring for System Performance

   Assessing the trend of general development and system performance
should not take large quantities of staff time and effort.  The
monitoring process should be established as follows:

      STEP 1   -  Collect data to assess changes in the major listed
                  items above.

      STEP 2   -  Compare changes to the trends forecasted.  If trends
                  appear as anticipated, do not continue through the
                  following steps and continue monitoring at the study
                  area level.


                                        DATA TYPE
                      USE  LATION MENT   GRAPHICFACILI- TRANS-
                                                 TIES  PORTATION

    Bureau of Census          X     X       X                     X

    US Department of
    Transportation                          X                     X


    Dept. of
    Transportation                                 X       X

    State Planning
    Agency             X      X     X       X

    Revenue Office                  X

    Motor Vehicle Dept.             X       X

    Employment Security       X


    Planning and
      Zoning           X      X     X       X

    Traffic Dept.                                  X       X      X

    Utility Dept.s            X

    Building and Permits      X             X

    Chamber of
      Commerce         X      X     X

    Public Transp. Agencies                                X      X

   SOURCE:  Worrall, R.D. & Robertson, S., Development of Information
            System for the Urban Transportation Planning Process,
            (Washington, DC, Transportation Research Board, 1973.

                                FIGURE 2
                        POTENTIAL SOURCES OF DATA


      STEP 3   -  If the monitoring program indicates travel demand or
                  development is not following the projected trends,
                  stratify the basic data monitored to assess the
                  geographic locations within the study area which are
                  deviating from projected trends.

      STEP 4   -  Determine if the deviations are in confined areas or
                  impact the entire study area.  If the problem is
                  local, assess the impact on the transportation system. 
                  If necessary, modify the development forecasts and the
                  forecast year plan, If problems exist areawide, the
                  analyst should evaluate the forecasts and the
                  transportation improvement program, Either modify the
                  long-range estimates or the policy on growth.

      STEP 5   -  If unexpected changes are occurring to the
                  transportation system for example, if vehicle miles of
                  travel is increasing rapidly or if transit patronage
                  is rapidly declining - the reason should be sought out
                  and appropriate action taken.  As with development
                  changes, forecasting procedures may require
                  modification or the transportation program may need to
                  be modified.

      STEP 6   -  In the event of major problems, Steps 3-5 should be
                  followed until the transportation planning process is
                  in harmony with growth trends.

Monitoring to Update Inventory Information

   Some of the inventory information will be updated when monitoring for
evaluating system performance as described in the previous section. 
Files on roadway volumes, for example, can be kept current when
collecting data using hose counts to estimate vehicle miles travelled
(VMT).  Any file requiring traffic analysis area data should not be
updated as specified by the normal monitoring schedule shown in the next
section.  Except in areas anticipating fast growth (greater than five
percent per year), the files should be updated concurrent with the
decennial census.  The primary purpose of these files is to supply input
to the system planning procedures.

   All information should be identified as to source and agency
responsibility.  Data such as changes in land use will generally be on
file with the local office of planning and zoning, and can easily be
shared with the transportation study staff.  Supported by certificates
of occupancy issued to new developments, the data sources will be
prepared to respond to an update at a small geographic analysis area

Scheduling of Data Items to be Monitored

   Monitoring the primary data items should be scheduled as part of the
overall transportation planning process.  A suggested schedule for
monitoring in areas experiencing moderate growth, between about two and
three percent per year, is shown in Table 5. All socioeconomic data are
intended to reflect areawide chances which occur during the monitoring
period.  Under the normal surveillance program, locating the changes
within the study area is not required.  The absolute change


                                 TABLE 5

                Communities Experiencing Moderate Growth

  DATA ITEM                      (Years)    LEVEL OF DETAIL

     Population                     2       Areawide
     Dwelling Units                 2       Areawide
     Employment (Total)             2       Areawide
     Auto Registrations             2       Areawide
     Land Use                       2       Areawide by category

  Transportation System
     Roadway Mileage                2       Functional Classification
     Vehicle Miles of Travel        2       Functional Classification
     Transit Revenue Vehicle Miles  2       Areawide
     Transit Revenue Passengers     2       Areawide
     Transit Total Passengers       2       Areawide
     Transit Service Area
       (1-4 Mile Bandwidth)         4       Areawide
     Transit Vehicle Age
       Distribution                 2       Areawide

Source:  U.S. Department of Transportation, Data for Urban
         Transportation Planning, (Washington, D.C., 1978)


in population or dwelling units, auto registrations and employment can
be compared to the expected growth rate between the base year and
forecast year to determine if the actual growth is following the
anticipated growth trends.

   Land use should be tabulated using the categories currently in use
within the small urban area.  The following categories will provide
sufficient detail:

         -  Residential
         -  Commercial
         -  Industrial
         -  Open Space
         -  Other (i.e., streets, power substations, etc.)

   Roadway mileage should be tabulated by functional classification as
described in Chapter One.  The monitoring of system change should be
consistent with the inventory.  Changes in roadway mileage do not serve
as an indicator of system performance.  However, coupled with changes in
vehicle miles of travel by functional classification, the use of each
roadway type can be monitored.

   Monitoring the transit data listed in Table 5 is recommended, based
on the Urban Mass Transportation Administrations Uniform System of
Accounts and Records.13/ The system is structured around fixed-route
transit service but can be adapted to demand-responsive service as well. 
For demand-responsive service, the 1-4 mile service area should be   
defined as the total service area of the system.  Transit vehicle data
should be collected for the following age groups:

         -  Under 5 years old
         -  5-9 years old
         -  10-14 years old
         -  15-19 years old
         -  19+ years old

Vehicle data will be useful for monitoring average fleet age and transit
vehicle replacements.

   System operations obtained through discussions with various
individuals should not be overlooked when evaluating the transportation
system performance.  They include discussions with the traffic engineer,
law enforcement agencies and the citizenry.  Through their daily
personal involvement, they can provide useful information for
maintaining a viable transportation system.

                         MONITORING TRAVEL DATA

   Two categories of travel data will be discussed here - roadway travel
and public transportation travel.  Techniques are presented for
estimating the magnitude of travel for each.  Travel data provides the
key indicator of system performance and is of great assistance for
operational planning in addition to system planning.  Many urban areas
collect traffic volume data, or a State or county agency might collect
the data.  The existing sources should be sought out prior to collecting
new data in order to coordinate the programs.


Roadway Data

   Roadway use is, usually measured by vehicle counting through the use
of automatic traffic counters.  The procedure was. discussed in Chapter
One.  Also, as discussed in Chapter one, roadside interviews along major
arterials and freeways define travel associated with trip origins and/or
destinations outside the study Area.

   In addition to a traffic counting program it is also desirable to
monitor auto occupancy.  Changes in auto occupancy rates can
significantly influence the amount of vehicle miles of travel in an
urban area.  Historically, the auto occupancy rate has remained fairly
stable.  Because of the promotion of ridesharing programs and growing
concerns over energy consumption, more significant changes in the auto
occupancy rates is likely.

   Estimating VMT from counts and roadway segment mileage is done by the
State and can be extended to include the transportation planning study
area.  A variation of this technique involves application of sampling
procedures for estimating VMT.  Details of the sampling procedure are
included in the Guide to Urban Traffic Volume Counting. 1/

   With VMT being highly dependent upon auto occupancy, it is
recommended that the average auto occupancy for the study area be
reevaluated regularly when reporting VMT.  In areas of moderate growth,
every two years will be adequate.

   The procedure for monitoring auto occupancy is not complicated.  It
requires, in addition to automatic traffic counters at designated
locations, personnel equipped with hand counters to classify the
vehicles passing the location according to the number of people in the
vehicle.  The counter should be a standard classification traffic
counter with six or more meters to tabulate the number of vehicles with
from one to six or more occupants.

   For further detail on obtaining auto occupancy information, consult
the Guide to Estimating Urban Vehicle Classification and Occupancy. 14/

Public Transportation Data

   Data collection for public transportation systems is required for
proper operational planning as well as for monitoring the total
transportation system.  Changes in ridership demand and travel patterns
must be responded to promptly in order for public transportation systems
to capture new markets and continue to serve their existing clientele
more expeditiously.

   Three procedures can be employed for monitoring transit ridership in
the urban areas.  They are:

         -  Onboard origin-destination surveys
         -  Load point checks
         -  Ride checks


   The onboard origin-destination survey, presented in detail in the
Transit Planning manual, provides considerably more information than the
latter two techniques but is also more costly.  In the small urban areas
where public transportation coverage is not extensive, the utility of
the onboard survey is limited.

   Passenger load checks are designed to collect data economically for
fixed-route transit service and can collect information about more than
one route at the same time - depending on location.  Locations along the
transit route are generally selected for proximity to the maximum load
point of the route.

   Figure 3 shows a typical form for use in load point checking.  The
data provide information on the schedule adherence of vehicles,
passenger loads as compared to seats available and boarding/alighting
activity at that particular location.

   Load point checking should be a regular activity at or near the
maximum load points of transit routes.  Each major load point should be
checked monthly in the smaller urban areas.  Checks should be for two
consecutive days over a six hour period.  The six hour period may begin
at 6:00 a.m., or with the first a.m. trip past the check point.  It may
also end at 6:00 p.m., or the last p.m. trip past the check point, where
the afternoon and p.m. peak periods are under investigation.

   The six hour period will cover the peak and base operations.  Using
consecutive day checks will allow the analyst to resolve variations
peculiar to a specific day of operation.  Checking should be done for
typical operating days (normally Tuesday through Thursday) and, except
for special operational studies, holidays should be avoided.

   Load point data are affected by the weather.  Inclement weather
causes abnormal fluctuations in ridership and should be avoided even if
it requires last minute manpower scheduling changes.  The data gathered
are of importance to the operator as well as the local planner for
evaluating system performance.

   Ride checks require an individual to ride a transit vehicle and
monitor the number of passengers boarding and alighting at each bus
stop.  Ride checks can be used to profile the ridership along a fixed
route or they can be used to profile trip activity of a demand-
responsive system.  For demand-responsive activities, the ride check
does not require an individual to ride the vehicle, since a central
dispatcher is controlling the stops.  The dispatcher's log provides the
same information as a ride check provides on a fixed route.

   Figure 4 is a typical form layout for ride checks.  Comparison with
the load point checking form reveals the following major differences:

         -  A separate form is necessary for each vehicle.

         -  Data are compiled on the form for each stop along the route.

   Each bus line or demand-responsive service area should be surveyed
quarterly for operational planning, although such frequent monitoring is
not required for general system monitoring.


Click HERE for graphic.

                                FIGURE 3
                      TYPICAL LOAD POINT CHECK FORM


   Ten percent of the vehicle trips should be included in the survey. 
The trips surveyed should reflect operations over the full operating
day.  Data from fixed-route service can be used to develop a ridership
profile for the bus line or, where multiple bus lines operate over the
same street, for the street.  Data from demand-responsive service can be
used to develop a transit trip matrix and develop a mapping of major
travel desires via public transportation.

   Sample data collected from ride and load point checks can be combined
with farebox revenue records to assess changes in the system.  Comparing
the farebox revenue to ridership on a day when checks are made allows
for the development of a revenue/ridership relationship.  As revenue is
monitored, fluctuations in revenue can be interpreted to describe
fluctuations in demand.

   Fare policy changes will also be evident in the revenue analysis.  If
fares chance or the mix of ridership changes--more senior citizens
riding the system at reduced fares, for example--the revenue analysis
will require adjusting.

   A reinventory of the revenue vehicle fleet related to public
transportation service will normally be conducted annually, although for
most small urban areas it is only required every two years.  Changes in
major capital investments are slow to occur; therefore, the data update
should be relatively simple.  Vehicle age, mechanical status and
availability should be verified with the operators providing public
transportation service within the study area.

   With the above travel data and a regular monitoring of revenue, the
monitoring program will satisfy the information requirements for
operational planning and, therefore, the data reporting requirements of
the transportation planning study.


   Changes in land use will account for the major changes in employment
and population of an urban area.  Monitoring these changes will provide
the transportation planning staff with details necessary to assess
growth trends.

   Two data sources are recommended for monitoring land use changes. 
The first source is the submittals required by the city or county
planning and zoning agencies for construction and other business
purposes.  This provides a tabulation of anticipated change and,
therefore, can be used to forecast change for approximately a five year
period.  The second source is either certificates of occupancy or
electric meter installations.  These data will show actual changes in
land use.

   The transportation planning study staff should receive major
development submittals from the planning and zoning agency together with
as much of the detail development plan as practical.  Residential
developments will be defined as to structure type and density in terms
of units per acre.  Commercial developments will specify the use type
and gross floor area.  Traffic impact statements are usually required
with the development plan and will include estimates such as Population,
employment, and travel demand.


Click HERE for graphic.

                                FIGURE 4


   Development plans should be mapped as, an overlay to the existing
land use inventory to note changes, Comparisons should be made to
determine if the actual plans are in conformance with the forecast
estimates.  Since the same procedure should be used for forecasting land
use., a significant variance would not be expected for some years after
the initial plan preparation year.

   After construction and prior to opening, each new structure is
generally issued, by law, a certificate of occupancy signifying it has
satisfied all building requirements.  Tabulating the certificates of
occupancy by land use type will provide an up-to-date file of
residential, commercial and industrial development.  For large
commercial and industrial developments, the planning staff should
contact the owner/occupant to inquire about the number of employees

   If certificates of occupancy are not available, the new development
can be monitored through the electric utility company when it installs a
new electric meter.  Large employers should be interviewed by telephone
to determine the employment level anticipated.

   When updating land use files and maps to a current year, the analyst
should remember to make appropriate changes to the land use categories
which the new development replaces.  Generally, this will represent a
modification to the open space or vacant land files.

   To estimate the population served by public transportation for the
current monitoring year, the analyst must convert dwelling unit changes
into population.  Dwelling units accumulated by traffic analysis area
can be converted to population using the rate for other residential
developments in the analysis area, or, if it is the only residential
development in the analysis area, the areawide rate as determined from
the census data or base year data files.


                              CHAPTER THREE


   The primary purpose of forecasting is to provide information for
transportation system planning.  It is recommended that forecasts be
limited to the data items required for system planning.  The specific
variables needed are based upon the procedures described in the System
Planning manual.  The data items are as follows:

            -  Population and Dwelling Units
            -  Mean Income
            -  Auto Ownership
            -  Retail Employment
            -  Non-Retail Employment

   The actual data sources used in each urban area will depend on data
availability and the current level of effort in the urban area devoted
to planning.  The approach here is to provide direction for finding data
that can assist the transportation analyst, assuming that forecast data
is not available for small geographic areas.

   The user should consult the 1970 Census User's Guide 9/ to identify
specific variables for measuring residential and employment activities. 
In addition, the Obers Projections 15/, will provide aggregate forecasts
of the appropriate data.  These references will also be helpful in
preparing forecasts of auto ownership and income distribution.


   To forecast population, first review the existing land use plan to
determine the growth potential of the study area.  This review must be
balanced against development requirements for employment sites to
maintain a balance in the labor participation rates. 15/ Second, the
historical growth trends should be plotted to develop a realistic
picture of the probable growth of the urban area. 16/  Unless the
community has a policy for encouraging major growth, it is unlikely that
the rate of growth will change drastically.  The historical rate of
change of persons per dwelling unit should be plotted to determine
trends in household size, since dwelling units will probably be selected
for estimation at the traffic analysis area level.  The trend will
provide insights for obtaining totals at the areawide level.

   The analyst will also wish to review the growth proposed for the
study area as it relates to the growth of the State as a whole.  The
State planning agency will have forecast information and their data may
be useful for establishing a total for the study area.


   National projections of population and employment are prepared for
the United States Departments of Commerce and Agriculture using the
Bureau of Economic Analysis (BEA) geography. 15/ This source subdivides
the United States into 173 economic analysis areas.

   Forecasts are made for each area based on distribution of national
growth.  The data can be used to develop totals for the study area based
on growth rate and base year population.  The information provided
includes, through the year 2020:

         -  Population
         -  Per Capita Income
         -  Total Employment

   The following procedure can be used to estimate population and
dwelling units for each traffic analysis area:

      STEP 1   -  Determine the areawide population control total from
                  local sources or those mentioned above.

      STEP 2   -  Determine the areawide dwelling unit control total
                  using the population control total and the analysis of
                  household size.

      STEP 3   -  With the base year dwelling unit inventory and the
                  proposed residential development proposals (converted
                  to dwelling units), prepare the first estimate of
                  projected dwelling units in the traffic analysis area
                  and areawide.

      STEP 4   -  The first estimate will not agree with the control
                  total established in Step 2. An evaluation of the
                  distribution should be made with the transportation
                  study participants.  The majority of participants
                  should agree upon which traffic analysis areas should
                  be modified and the magnitude of each modification.

      STEP 5   -  Perform the modifications to determine a second
                  estimate of dwelling units at the traffic analysis
                  area level.

      STEP 6   -  Factor the second estimate by the ratio of the
                  areawide control (Step 2) to the areawide total from
                  the second estimate to produce the dwelling units per
                  traffic analysis area.  These are the numbers to be
                  used in forecast scenarios.

      STEP 7   -  Reapply the analysis area factors found in Step 6 to
                  convert population to dwelling units and the
                  population estimates by traffic analysis area will be

                          MEAN HOUSEHOLD INCOME

   Two phases can be used for estimating the mean household income for
each traffic analysis area and preparing the estimates for input to the
trip generation procedures.  In phase I the forecast year mean household
income is estimated for the


analysis area.  In phase II the average is refined to determine the
percent of dwelling units estimated to be in each income stratum.

Phase I - Mean Income Estimation

   Mean household income for traffic analysis areas should be part of
the inventory described in Chapter One.  A basic source for such data
would be the decennial census.  Using information that may be available
through the State, data developed on a county level, or Obers
Projections, the income can be updated to a forecast year.  Dollar
values should be adjusted to the base data year using the consumer price
index as described in the System Planning manual.

   The new residential developments identified as the "second estimate"
(Step 5 of the previous section) should be analyzed to determine the
estimated average income each will contribute in the traffic analysis
area.  Average income may be estimated by looking at other housing in
the same analysis area or looking at another analysis area which has
comparable housing to see if the new development is comparable.  If the
new development is comparable to the existing housing, an income
adjustment is not necessary.  If the average income for the new develop-
ment is expected to differ from the current average income of the area,
the analysis should reflect the difference.

   A weighted average should be developed based on the number of
existing dwelling units multiplied by the existing average income and
the number of new dwelling units times their established average income. 
The resulting average will represent an update of the base year income

   The increase in per capita income can be applied to the updated base
year traffic analysis area average income values to obtain future
average income by small analysis area.  The analyst may use the revised
income values to apply the trip generation procedures described in the
System Planning manual.

Phase II - Distribution of Households by Income

   The income data for the analysis area can be refined to estimate the
number of households in each income stratum.  Several urban areas have
been analyzed for household distribution by average income distribution. 
Definite relationships have been found to exist. 17/

   Figure 5 shows the type of relationship that can be expected by
making graphs from decennial census data.  Once the revised average
income for the forecast year has been determined, the analyst can enter
a graph and determine the percent of households that can be expected in
each income stratum.  This procedure assumes that the income
distribution of households remains constant over time.

                             AUTO OWNERSHIP

   Auto ownership per household is an important trip related variable. 
Although not always required for trip generation (see System Planning
manual), the analyst should forecast auto ownership to develop an
areawide total.


Click HERE for graphic.

                                FIGURE 5


   Auto registration by year may be obtained from the motor vehicle
administration in the State summarized by city, town or county, In
States where an ad valorum tax is assessed on cars, registrations are
available from the tax assessor.-A plot of auto ownership within the
study area superimposed upon the number of dwelling units of the area
will show the trend of auto ownership per--dwelling unit.  Interpolated
values from the dwelling unit curves can be used with the auto
registration to get the annual ratio and allow determination of a rate
of change.

   The autos per household curve can be extrapolated to the forecast
year by extending past trends.  A forecast year rate can be determined. 
Applying the rate to the number of dwelling units anticipated in the
forecast year will yield a forecast year control total for autos within
the region.

   When applying the trip generation rates based on average household
income, the tables provide an estimate of autos per dwelling unit for
that income stratum.  Multiplying the auto rate times the number of
dwelling units will yield the number of autos in each traffic analysis

   To use auto ownership at the traffic analysis area level, the analyst
should factor the estimates derived from the trip generation procedures
so the areawide sum of autos is equal to the control totals developed
from local auto ownership trends.


   Forecasting employment follows the same general procedure as
forecasting population.  The same cautions are in order for arriving at
control totals to ensure they are in keeping with other planning at the
State level.  Also, the labor participation rate (employment/population)
should be reviewed to see if it follows past trends in the study area.

   Obers Projections 15/ provides past estimates as well as forecasts of
employment to the year 2020.  This is provided for a number of industry
classifications.  Using these data, employment can be forecast to
develop areawide control totals and estimates at the traffic analysis
area level.  The only significant difference between forecasting
population and employment is the requirement that employment forecasts
should be classified into retail and non-retail employment (see System
Planning manual).

   The steps required to develop forecast data for either employment
category are:

      STEP 1   -  Locate the major commercial developments anticipated
                  between the base year and the forecast year by traffic
                  analysis area.

      STEP 2   -  Using employee rates per acre or per gross floor area,
                  convert the development plans to employees and add the
                  employment to the base year totals.  The areawide sum
                  is the result of a first estimate of either retail or
                  non-retail employment.


      STEP 3   -  Compare the results from Step 2 with the areawide
                  control total and adjust as required through a
                  subjective evaluation,

      STEP 4   -  Modify the first estimate to arrive at a second
                  estimate of employment.

      STEP 5   -  Adjust the employees per traffic analysis area
                  uniformly so that the sum of employment is equal to
                  the regionwide control total.

   The results of Step 5 will be the employment forecasts that will be
used. in the trip generation procedures described in the System Planning



   1.  U.S. Department of Transportation, Federal Highway
       Administration, Guide to Urban Traffic Counting Manual,
       (Washington, D.C., 1980).

   2.  National Committee on Urban Transportation, Procedure Manual 3A
       Measuring Traffic Volumes, (Chicago, Public Administration
       Service, 1958).

   3.  Smith, W., Transportation & Policy for Tomorrow's Cities, (New
       Haven, 1966).

   4.  National Committee on Urban Transportation, Procedure Manual 2A
       Origin-Destination and Land Use, (Chicago, Public Administration
       Service, 1958).

   5.  Brant, A.E. & Low, D.D., "Cost Saving Techniques for Collection
       and Analysis of Origin-Destination Survey Data," Highway Research
       Record No. 205, (Washington, Transportation Research Board,

   6.  U.S. Department of Transportation, Federal Highway
       Administration, Urban Origin-Destination Surveys, Dwelling Unit
       Survey, Truck and Taxi Surveys, External Survey,_(Washington,

   7.  U.S. Department of Transportation, Urban Mass Transportation
       Administration, External Operative Manual, (Washington, D.C.,
       1972, amended).

   8.  U.S. Department of Transportation, Federal Highway
       Administration, Data for Urban Transportation Planning,
       (Washington, D.C., 1978).

   9.  U.S. Department of Commerce, Bureau of the Census, 1970 Census
       Users' Guide, (Washington, D.C., 1970).

  10.  Worrall, R.D. & Robertson, S., Development of Information System
       for the Urban Transportation Planning Process, (Washington, D.C.,
       Transportation Research Board, 1973).

  11.  Lagomarisino, L.C., & Matthias, J.S., Determining the Need for
       Updated Transportation Studies in Smaller Urban Areas,
       (Washington, D.C., Transportation Research Board, 1977).

  12.  National Cooperative Highway Research Program, Report 18, Quick
       Response Urban Travel Estimation Techniques and Transferable
       Parameters, Users' Guide, (Washington, D.C., Transportation
       Research Board, 1978).

  13.  U.S. Department of Transportation, Urban Mass Transportation
       Administration Uniform System of Accounts Records -
       Implementation, (Washington, D.C., 1977).

  14.  U.S. Department of Transportation, Federal Highway
       Administration, Guide to Estimating Urban Vehicle Classification
       and Occupancy, T-Washington, D.C.).


  15.  U.S. Water Resources Council, Obers Projection, Volume 2,
       (Washington, D.C., 1974).

  16.  U.S. Department of Commerce, Bureau of the Census, Guide for
       Local Area Population Projections, (Washington, D.C., 1977).

  17.  U.S. Department of Transportation, Federal Highway
       Administration, Trip Generation Analysis, (Washington, D.C.,

          U.S. GOVERNMENT PRINTING OFFICE : 1980 0-320-194/6268


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