Intelligent Transportation Systems
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Microscopic Analysis of Traffic Flow in Inclement Weather

Foreword

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.

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Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

Technical Report Documentation Page

1. Report No.

FHWA-JPO-09-066

2. Government Accession No.

EDL No.- 14498

3. Recipient’s Catalog No.

4. Title and Subtitle

Microscopic Analysis of Traffic Flow in Inclement Weather

5. Report Date

November 2009

6. Performing Organization Code

7. Author(s)

Hesham Rakha, Daniel Krechmer, Gustave Cordahi, Ismail Zohdy, Shereef Sadek, and Mazen Arafeh

8. Performing Organization Report No.

9. Performing Organization Name and Address

Virginia Tech Transportation Institute
3500 Transportation Research Plaza (0536)
Blacksburg, VA 24061

Cambridge Systematics, Inc.
4800 Hampden Lane, Suite 800
Bethesda, MD 20814

10. Work Unit No.

11. Contract or Grant No.

DTFH61-06-D-00004

12. Sponsoring Agency Name and Address

Research and Innovative Technology Administration
U. S. Department of Transportation
1200 New Jersey Avenue, SE
Washington, DC  20590

13. Type of Report and Period Covered

Guidelines

14. Sponsoring Agency Code

HOP

15. Supplementary Notes

COTM’s for FHWA are Roemer Alfelor and C. Y. David Yang.

16. Abstract

Weather causes a variety of impacts on the transportation system.  An Oak Ridge National Laboratory study estimated the delay experienced by American drivers due to snow, ice, and fog in 1999 at 46 million hours.  While severe winter storms, hurricanes, or floodings can result in major stoppages or evacuations of transportation systems and cost millions of dollars, the day-to-day weather events such as rain, fog, snow, and freezing rain can have a serious impact on the mobility and safety of the transportation system users.  Despite the documented impacts of adverse weather on transportation, the linkages between inclement weather conditions and traffic flow in existing analysis tools remain tenuous.  This is primarily a result of limitations on the data used in research activities.

The scope of this research included use of empirical data, where available, to estimate weather impacts on three categories of submodels related to driver behavior, longitudinal vehicle motion models (acceleration, deceleration and car-following models), lane-changing models and gap acceptance models.  Empirical data were used to estimate impacts of adverse weather on longitudinal and gap acceptance models but no suitable datasets were identified for lane-changing models.  Existing commercial microsimulation software packages were then reviewed to identify whether and how weather-related factors could be utilized in these models.  The various submodels used in these packages to estimate longitudinal motion, lane-changing and gap acceptance models were evaluated.  The research found that for the most part, weather-related factors could be incorporated into these models, although the techniques vary by package and by type of model.  Additional empirical research is needed to provide confidence in weather-related adjustment factors, particularly as relates to ice and snow.  This report concludes with some recommendations of future research related to weather and traffic flow.  Additional work is proposed related to human factors and microscopic traffic modeling.

17. Key Words

Weather, traffic flow, statistical models, human factors, microsimulation

18. Distribution Statement

No restrictions.

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No of Pages

119

22. Price

N/A

Form DOT F 1700.7 (8-72)                                                                       Reproduction of completed pages authorized

 

Metric Conversion Factors
(International System of Units)

APPROXIMATE CONVERSIONS TO SI UNITS
SYMBOL WHEN YOU KNOW MULTIPLY BY TO FIND SYMBOL

LENGTH

in

inches 25.4 millimeters mm

ft

feet 0.305 meters m

yd

yards 0.914 meters m

mi

miles 1.61 kilometers km

AREA

in2

square inches 645.2 square millimeters mm2

ft2

square feet 0.093 square meters m2

yd2

square yard 0.836 square meters m2

ac

acres 0.405 hectares ha

mi2

square miles 2.59 square kilometers km2

VOLUME

fl oz

fluid ounces 29.57 milliliters mL

gal

gallons 3.785 liters L

ft3

cubic feet 0.028 cubic meters m3

yd3

cubic yards 0.765 cubic meters m3

NOTE: volumes greater than 1000 L shall be shown in m3

MASS

oz

ounces 28.35 grams g

lb

pounds 0.454 kilograms kg

T

short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t")
TEMPERATURE (exact degrees)

oF

Fahrenheit

5 (F-32)/9
or (F-32)/1.8

Celsius oC

ILLUMINATION

fc

foot-candles 10.76 lux lx

fl

foot-Lamberts 3.426 candela/m2 cd/m2

FORCE and PRESSURE or STRESS

lbf

poundforce   4.45   newtons N

lbf/in2

poundforce per square inch 6.89 kilopascals kPa

 

APPROXIMATE CONVERSIONS FROM SI UNITS
SYMBOL WHEN YOU KNOW MULTIPLY BY TO FIND SYMBOL

LENGTH

mm

millimeters

0.039

inches in

m

meters

3.28

feet ft

m

meters

1.09

yards yd

km

kilometers

0.621

miles mi

AREA

mm2

square millimeters

0.0016

square inches in2

m2

square meters

10.764

square feet ft2

m2

square meters

1.195

square yards yd2

ha

hectares

2.47

acres ac

km2

square kilometers

0.386

square miles mi2

VOLUME

mL

milliliters

0.034

fluid ounces fl oz

L

liters

0.264

gallons gal

m3

cubic meters

35.314

cubic feet ft3

m3

cubic meters

1.307

cubic yards yd3

MASS

g

grams

0.035

ounces oz

kg

kilograms

2.202

pounds lb

Mg (or "t")

megagrams (or "metric ton")

1.103

short tons (2000 lb) T

TEMPERATURE (exact degrees)

oC

Celsius 1.8C+32 Fahrenheit oF

ILLUMINATION

lx

lux

0.0929

foot-candles fc

cd/m2

candela/m2

0.2919

foot-Lamberts fl

FORCE and PRESSURE or STRESS

N

newtons 0.225 poundforce lbf

kPa

kilopascals

0.145

poundforce per square inch lbf/in2

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