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Appendix E. Traveler Information Needs and Tutorials

This appendix contains supplementary information from the design tool. The first section is material related to optional Step 2a in the design tool which includes information about traveler information needs. The second section consists of the tutorials which provide background information on a travelers’ use of road weather information.

Traveler Information Needs

This section provides additional recommendations about the type of information that travelers are likely to need when making certain travel decisions. The guidance in this section can be used to identify information elements that can be included in a road weather message so that it better matches what information travelers are looking for when they seek out road weather information.

Each travel decision is discussed separately using the following layout:

The recommendations about traveler information needs in this chapter are provided in separate sections organized according to travel decisions. Table E-1 below indicates on which page the recommendations for each travel decision can be found. The pages that immediately follow the table below provide some background information about how some of the recommendation information about traveler information needs were identified.

Table E-1. Traveler Information Needs Look-up Table showing where to find information about each travel decision.
Travel Decision Page
Expect delays Travel Decision 1
Change route Travel Decision 2
Change travel mode Travel Decision 3
Drive with caution Travel Decision 4
Change driving behavior Travel Decision 5
Make safety-related preparations Travel Decision 6
Cancel trip Travel Decision 7

 

Table E-2. Key DMS message element definitions (adapted from Dudek, 2004).
Message Element Definition
Weather Descriptor* Informs the traveler of the unusual situation
Location* Informs the traveler of the location of the unusual situation
Lanes Closed (Blocked) Gives specific information about which lanes or exit ramps are closed or blocked
Closure Descriptor Used in place of the Weather Descriptor when all lanes on the facility or exit ramp are closed
Location of Closure Used in place of the Location and states the location of the freeway closure
Effect on Travel Informs the traveler of the severity of the situation and helps the traveler decide if a diversion is appropriate
Audience for Action Used when the Action message component applies to a specific group of travelers rather than all travelers who see the DMS
Action Tells the traveler what to do
Good Reason for Following the Action Gives the traveler confidence that following the advice on the DMS will result in safer travel and/or significant time savings

* The names of these message elements were changed to apply more generally to weather conditions.

Travel Decision 1: Expect Delays

Introduction

This travel decision applies when it will take drivers longer than normal to travel on certain roadways. Many travelers, especially commuters, are averse to travel delays and will alter their travel plans to avoid delays (e.g., Haselkorn & Barfield, 1990). There appears to be a lower bound to what most travelers consider a delay, which seems to be around 10 to 15 minutes longer than normal travel (Ullman, Dudek, and Balke, 1992; Huchingson and Dudek, 1979).

How can travelers use the information?

Available Traveler Actions Travelers who Benefit from this Information Key Information Needs Dissemination Issues
Plan for delays All
  • Length of delay
  • Location of delay
None
Leave later Travelers with flexible schedules (e.g., not typically commuters or CVO drivers)
  • Need to know that conditions are expected to improve
En-route methods are unsuitable because the trip has started
Leave earlier All
  • Information must be available early enough for travelers to arrange to leave earlier
En-route methods are unsuitable because the trip has started

 

Discussion

The primary action associated with this travel decision is planning for delays because it is available to all drivers during most of their travel. This action involves travelers adjusting their schedules to take into account the delay. Tutorial 1 discusses the frequency of traveler trip time changes. Travelers can most readily use this information before they depart, however, it is still useful en-route if they can phone ahead to warn others of their delays. Tutorial 2 discusses the suitability of making this travel decision at various trip stages. The key information is the duration of the delay, since it will determine the traveler’s course of action. For short delays, travelers may decide that their plans are not affected in important ways. For example, Ullman et al. found that it wasn’t until delay times reached 15 minutes that 50% of drivers asked would consider a diversion to another route. Another notable finding is that the phrasing of a delay message influenced driver willingness to divert to another route. In particular, using “save X min” lead drivers to consider diversions sooner than “X min delay” (Ullman, Dudek, and Balke, 1992; Huchingson and Dudek, 1979).

The options related to changing departure time are sub-sets of the “plan for delays” action and typically apply to travelers who receive the information prior to leaving and that also have the flexibility to change their schedule. Note that drivers will make decisions related to planning for delays in other weather-related situations, since traffic disruptions are a common impact associated with several types of weather events. Apart from traffic-flow disruptions, another situation in which a delay is unavoidable is if drivers cannot reach a destination using certain roads, and travelers are required to reroute, which will likely add to travel time.

Expect Delays: Short Text/Visual Message Examples

For a short text/visual message, the key message elements are presented below, with each line corresponding to a DMS message line. For other short text message formats, the message elements are not required to be presented on separate lines; however if space is available, doing so may facilitate message comprehension.

Blank header cell. Message Elements
Baseline Message Message Without Recommended Action
Line 1 Weather Descriptor Weather Descriptor
Line 2 Action Location*
Line 3 Delay Information (Good Reason for Following the Action) Delay Information (Effect on Travel)
Example
  1. WATER ON ROAD
  2. TAKE US-23
  3. SAVE 20 MIN
  1. WATER ON ROAD
  2. AT EXIT 12
  3. 20 MIN DELAY

* Optional line

Expect Delays: Example Features or Information for Open Format Text/Visual Messages

Website or other open-format features or content that provide information that supports traveler decision making are shown in the table below.

Useful Display Features Information Elements

Traffic Map

Screen capture of website traffic map.
  • Location and magnitude of delays (colored roads)
  • Location of information (non-gray roads)
  • Location of traffic cameras

Traffic Camera

Camera image from traffic website.
  • Camera image allows drivers to see the congestion levels and conditions on the road
  • Time and location of camera image

Other Text Information

  • How long the weather events causing the delay conditions are expected to last
  • Description of the weather event so that drivers can infer the above information based on what they know of the weather event

 

Expect Delays: Auditory Message Example

An example HAR or 511 auditory message that is consistent with the auditory message guidelines provided in this report is shown below for this travel decision.

Source: Adapted from HAR Message Development Guide

 


 

Travel Decision 2: Change Route

Introduction

This travel decision most importantly applies when travelers cannot reach a destination using their intended route or taking an intended route is highly inadvisable. In the context of road weather conditions, this can involve the closure of roads, such as mountain passes, or roadways that are at risk of flooding. However, the decision to change routes is a common decision by certain types of drivers (Tutorial 1), such as those familiar with the road network, and these drivers will make this decision in other situations than just road closures.

How can travelers use the information?

Available Traveler Actions Travelers who Benefit from this Information Key Information Needs Dissemination Issues
Get off current route All drivers, but non-local or non-commuter drivers may have difficulty re-routing on their own
  • Route is impassible or closed
  • Location of problem, if it is restricted to a specific area or location
Not ideal on roadways frequented by recreational or out-of-area travelers
Take specific alternate route All drivers
  • Route is impassible or closed
  • Options for alternative routes
None

 

Discussion

The primary way in which drivers would likely use this information is if they cannot reach their destination using certain routes and have to find an alternative route. The key information in this case is that the route is impassible or closed, and this information should be part of any messages providing route-change information. To the extent that it is feasible, providing additional information about suitable ways to exit closed or impassible routes and information about alternative routes helps drivers unfamiliar with the road network. The table below provides message examples for communicating diversions to specific other routes (from Dudek, 2004). The messages are divided into normal diversions and pre-established diversion routes such as detours. Note that Dudek (2004) also recommends that for diversion routes that are not pre-established, the DMS operator should know the conditions on the alternate route before advising travelers to divert to that route, which generally requires electronic and/or human surveillance. Tutorial 2 discusses the suitability of making this travel decision at various trip stages.

Another useful message element is information about where the closed or affected area is located. This is helpful even if there is no diversion information because familiar drivers may be able to find their own suitable alternative routes, or reject alternatives that may still be in the affected regions. Also, travelers unfamiliar with the area would at least have the option of using other methods, (e.g., maps) to identify the problem location and find suitable alternative routes.

Example messages for route changes on specified other routes for normal diversions and pre-established diversions.

Diversion Condition Action Elements
Normal Diversion
  • EXIT AND USE [highway name, street name, route number]
  • EXIT AT [highway name, street name, route number]/
    USE [highway name, street name, route number]
  • TAKE [exit ramp name] EXIT
  • TAKE [exit ramp name] EXIT/
    USE [highway name, street name, route number]
  • TAKE EXIT [exit ramp number]
  • TAKE EXIT [exit ramp number]/
    USE [highway name, street name, route number]
  • TAKE [highway name, street name, route number]
  • TAKE [highway name, street name, route number]/
    USE [highway name, street name, route number]
  • TAKE NEXT EXIT
  • TAKE NEXT [number] EXITS
  • USE [highway name, street name, route number]
  • TUNE RADIO TO [number] AM (or FM)
Pre-established Diversion
  • EXIT AND FOLLOW DETOUR
  • EXIT AND FOLLOW SIGNS
  • EXIT AT [highway name, street name, route number]/
    FOLLOW DETOUR
  • EXIT AT [highway name, street name, route number]/
    FOLLOW SIGNS
  • TAKE [exit ramp name] EXIT/
    FOLLOW DETOUR
  • TAKE [exit ramp name] EXIT/
    FOLLOW SIGNS
  • TAKE EXIT [exit ramp number]/
    FOLLOW DETOUR
  • TAKE EXIT [exit ramp number]/
    FOLLOW SIGNS
  • TAKE [highway name, street name, route number]/
    FOLLOW DETOUR
  • TAKE [highway name, street name, route number]/
    FOLLOW SIGNS
  • TAKE NEXT EXIT

Each verb used in the above diversion action elements has a slightly different meaning. When creating original diversion messages, keep in mind the following definitions (from Dudek, 2004):

  • USE: a route that carries travelers to their destination (which may be their original route)
  • TAKE: a directive to begin the first “leg” of the route (which should connect with the current route)
  • FOLLOW: traveler will be guided by other signs along the route
  • EXIT: sometimes used as a verb with a highway name, street name, or route number (not an exit number)
  • GO: not used in DMS messages, but sometimes used in HAR messages

 

Change Route: Short Text/Visual Message Examples

Communicating that a route is impassable using a DMS can be more challenging for weather conditions than typical road-closure situations because the causes may be less localized than usual. For example, heavy snow may affect a road and the nearby alternative routes to a similar degree, whereas crash or roadwork-related closures would be localized to a single road.

For a short message, the key message elements are presented below, with each line corresponding to a DMS message line. For other short text message formats, the message elements are not required to be presented on separate lines; however if space is available, doing so may facilitate message comprehension.

 

Blank header cell. Message Elements
Diversion to Specific Route Diversion to Non-Specific Route
Line 1 Location of Closure Weather Descriptor
Line 2 Weather Descriptor Location
Line 3 Action Delay Information (Effect on Travel)
Example
  1. I-5 CLOSED AHEAD
  2. DEEP WATER
  3. TAKE NEXT EXIT
  1. I-5 CLOSED AHEAD
  2. DEEP WATER
  3. USE OTHER ROUTES

 

Change Route: Example Features or Information for Open Format Text/Visual Messages

Drivers can benefit from map-based information showing the affected roads or region, in addition to alternative routes that are unaffected or less affected by the weather event.

Useful Display Features Information Elements

Route Map

Screen capture of website traffic map.
  • Location/extent of problem or closure
  • Color coded major roads affected
  • Visual depiction of alternative roads that are unaffected or less affected by the conditions

Text Information

DUE TO A ROCK SLIDE, I-40 IS CLOSED IN BOTH DIRECTIONS BETWEEN EXIT 20 (U.S. 276), 24 MILES WEST OF ASHEVILLE, IN NORTH CAROLINA AND EXIT 421 (I-81 INTERCHANGE), EAST OF KNOXVILLE IN TENNESSEE.

Travelers can still reach Western North Carolina. The road is not expected to reopen for several months.

Official Detour: Motorists traveling on I-40 West are advised to take Exit 538, I-240 West. Follow I-240 West to Exit 4A, I-26 West. Follow I-26 West (a North Carolina Scenic Highway) to I-81 South. Take I-81 South and follow back to I-40, Mile Marker 421, in Tennessee. This route is 53 miles longer than I-40.

For a map of detour routes and the affected road closure, please click here.

  • Location of affected area
  • Text description of alternate routes
  • Ways to exit the closed route

 

Change Route: Auditory Message Examples

An example HAR or 511 auditory message that is consistent with the auditory message guidelines provided in this report is shown below for this travel decision.

*Statements in brackets [ ] are optional
Source: HAR Message Development Guide

The following message is more suitable for HAR usage than 511 due to its length and listing of alternate telephone numbers.

Example: Diversion onto a Specific Route

*Statements in brackets [ ] are optional
Source: HAR Message Development Guide

 


 

Travel Decision 3:  Change Travel Mode

Introduction

This involves the decision to switch from one travel mode to another.  The primary reason for making this decision is if one mode is significantly delayed or non-operational (e.g., transit disruptions).  However, some drivers (Tutorial 1) who have a flexible schedule, may also change from driving to other modes based on weather conditions (e.g., biking on a sunny day, getting a bus ticket to go skiing for the day if it is snowing).  Additionally, the decision to switch from driving to transit may also be a component of campaigns to reduce driving, such as ozone reduction days.

How can travelers use the information?

Available Traveler Actions Travelers who Benefit from this Information Key Information Needs Dissemination Issues
Switch from transit to other modes like driving Primarily transit users and commuters who use transit some of the time
  • Weather impacts on transit operations (delayed or cancelled)
  • Weather conditions make taking transit undesirable
Transit websites may be the primary information source
Switch from other modes to transit Older drivers and drivers with flexible schedules
  • Weather conditions are favorable for transit
  • Road weather conditions are unfavorable for driving
Regular weather forecasts may be the primary information source
Switch between other non-transit modes “Fair weather” bicyclists and commuters
  • Weather conditions are favorable for other modes
Regular weather forecasts may be the primary information source

 

Discussion

One implementation issue with regard to supporting the travel decision to switch away from transit (because of delays or cancelations) is whether a road weather message is the most appropriate place for this information.  If travelers are concerned about transit operations, a logical place to obtain that information is from a transit-related information source (e.g., transit website).  Providing information about transit disruptions alongside road weather information maybe more of a convenience to travelers (i.e., they can get all their road-related weather/travel information from a single source).  However, this requires that the transit information be accurate and timely, so a better way to provide this convenience is via a link to transit information.  Note that a DMS message is not useful because travelers will not view that message until after their decision is made, however, other short text messages alerting of transit disruptions are still appropriate.  Tutorial 2 provides additional guidance regarding the trip stage at which it is most suitable to convey mode change information.

In contrast, the decision to switch from driving to transit is one that can be made more easily if transit information is available in the same place as road weather information.  In this case, drivers could see that road weather conditions may be unfavorable, but that transit operations are on schedule/still operating and decide to forgo driving.  Another version of this travel decision may apply under fair weather conditions.  In this case, some travelers may decide to avoid driving and bicycle or walk to enjoy the nice weather.  Note that regular weather forecasts are probably more likely to be the primary source of information for travelers making this decision, since they focus more on future weather conditions.

A special case of this travel decision involves switching away from driving based on transportation management campaigns, such as those designed to reduce ozone levels.  This type of message is different in nature than most road weather information, unless travel restrictions are based on real-time conditions.  Otherwise, the key information in this case is just a reminder to drivers familiar with the program about implementation details, such as when certain vehicle groups are not supposed to drive.  On its own, this type of message is insufficient to communicate the details of the campaign, but participating drivers can be assumed to be already familiar with these details.

Change Travel Mode: Short Text/Visual Message Example

For a short message, the key message elements are presented below, with each line corresponding to a DMS message line.  For other short text message formats, the message elements are not required to be presented on separate lines; however if space is available, doing so may facilitate message comprehension.

Blank header cell. Message Elements
Phase 1 Phase 2
Line 1 Weather Descriptor Audience
Line 2 Location Recommended Action
Line 3 Effect on Travel Empty cell.
Example
  1. THICK FOG
  2. ON BAY BRIDGE
  3. 45 MIN DELAY
  1. SAN FRANCISCO
  2. TAKE BART

 

Change Travel Mode: Example Features or Information for Open Format Text/Visual Messages

Website or other open-format features or content that provide information that supports traveler decision making are shown in the table below.

Useful Display Features Information Elements

Transit Map

  • Route map for available transit resources so drivers can determine the feasibility of changing modes

Screen capture of a regional transit route map.

Text Information

  • Links to transit websites
  • Box displaying transit information such as departure times, any delays
  • Transit schedules

Screen capture of transit route planning tool.

 

Change Travel Mode: Auditory Examples

An example HAR or 511 auditory message that is consistent with the auditory message guidelines provided in this report is shown below for this travel decision.

 

 


 

Travel Decision 4:  Drive with Caution

Introduction

This travel decision is one that drivers should make when the road weather conditions are such that driving in a normal way (e.g., at full speed, not paying full attention to the road, etc.) may pose a safety risk.  The primary reason to provide this information is to alert drivers to be more careful, or to pay greater attention to their driving environment.  Note that the overall tone of this type of message is as an advisory or informational warning, not one that directs or “commands” drivers to act in a specific way.  The frequency of this travel adjustment is shown in Tutorial 1.

This travel decision recommendation is similar to the one on changing driver behavior (Travel Decision 5); however, the key differences are that the current recommendation involves 1) road weather conditions that are likely to be less severe, and 2) the primary adjustments in behavior required from drivers are simply extra care and attention to driving with regard to certain hazard conditions.

How can travelers use the information?

Available Traveler Actions Travelers who Benefit from this Information Key Information Needs Dissemination Issues
Drive with greater alertness / caution All drivers
  • Driving conditions are not normal and require caution or attention
  • Specific information about hazards that may not be easily perceived (e.g., black ice)
  • Location information if it is not directly implied in the dissemination method (e.g., DMS location)
Most effective when information is communicated in vicinity of hazard (Tutorial 2)

 

Discussion

A key assumption with communicating this type of information is that the simple alerting of drivers to conditions is sufficient, and that responsibility for taking greater care resides with individual drivers.  It is not currently known how well drivers comply with these types of advisory messages, and it is likely that some drivers will ignore this type of information.

An important use of this type of advisory information is to warn drivers of potentially hazardous conditions that are not immediately apparent to drivers, such as black ice, icy roads, high winds, etc.  Following this logic, if there are two different weather conditions that warrant the same “use caution” type message, the condition that is less obvious to drivers should be given priority.  For example, it is more useful for a driver to receive a warning about black ice that they cannot see, than fog, which drivers can easily see for themselves.

Location information is also important in this type of message if it is not directly implied by the dissemination method.  If the hazardous conditions are not near the DMS, location information should be provided if possible.  On a DMS, the caution information will be interpreted as being on the road ahead.  If this is not the case, then more specific location information should be provided.  This is important, because if drivers’ experiences do not match the advisory information, then drivers may perceive this type of information as unreliable and be more likely to disregard this information in the future.  See the guideline on communicating geographic extent (Guideline 27) for additional information. 

Note that Guideline 01 recommends avoiding the use of the word “caution” in a short text message because drivers may not always interpret the word’s meaning properly.  However, when used as described in the current recommendation, the word “caution” is acceptable because the phrase specifically applies to the situation and it describes precisely what drivers should do.

Drive with Caution: Short Text/Visual Message Examples

For a short message, the key message elements are presented below, with each line corresponding to a DMS message line.  For other short text message formats, the message elements are not required to be presented on separate lines; however if space is available, doing so may facilitate message comprehension.

Blank header cell. Message Elements
Baseline Message Message Without Recommended Action
Line 1 Weather Descriptor Weather Descriptor
Line 2 Weather Descriptor Location
Line 3 Location Empty cell.
Example
  1. ICY ROADS
  2. NEXT 4 MILES
  3. USE CAUTION
  1. ICY ROADS
  2. NEXT 4 MILES

 

Drive with Caution: Example Features or Information for Open Format Text/Visual Messages

Website or other open-format features or content that provide information that supports traveler decision making are shown in the table below.

 

Useful Display Features Information Elements

Route or Area Map

Screen capture of route map.
  • Location/extent of problem
  • Color coded major roads or areas affected by weather event

Text Information

Screen capture of road conditions in a written format.
  • Location of affected area
  • Text description of recommended actions

Camera

Webcam image of a roadway segment.
  • Camera image allows drivers to get a better sense of the severity of the conditions (note: some conditions such as black ice will not appear in a camera image)

 

Drive with Caution: Auditory Message Examples

The following messages are more suitable for HAR usage than 511 due to their length.

Example: Be Alert for Black Ice


*Statements in brackets [ ] are optional
Source: HAR Message Development Guide

Example: Watch Out for Snow Plows


*Statements in brackets [ ] are optional
Source: HAR Message Development Guide

Example: Be Alert for General Hazardous Conditions


*Statements in brackets [ ] are optional
Source: HAR Message Development Guide

 


 

Travel Decision 5: Change Driving Behavior

Introduction

This decision is similar to the one involving driving with caution, however, it is typically related to more severe conditions and involves providing information about specific actions that drivers should take to improve their driving safety. A key element is that there is a specific action or change in driving behavior (e.g., driving below a certain speed) that would be reasonably expected to reduce crash risks under those conditions. The safety implications of presenting road weather information are discussed in Tutorial 4.

How can travelers use the information?

Available Traveler Actions Travelers who Benefit from this Information Key Information Needs Dissemination Issues
Drive slower / below a specified speed All
  • Driving at normal speed is unsafe
  • Recommended safe speed
Most effective when information is communicated in vicinity of hazard
Get out of a lane All
  • There is a hazard in a particular lane that drivers should leave in order to avoid
Expect high winds CVO drivers, RV drivers, etc.
  • High wind conditions
Leave greater headway All
  • There is low traction or leaving greater headway is safer
Turn on headlamps All
  • Visibility is reduced or can be improved by turning on headlamps

 

Discussion

All of the available traveler actions listed above have the same basic nature, but are specifically related to different types of road weather hazards. Related to this, it is important that the recommended action be viewed as a reasonable action to take given the driving hazard (e.g., turn on lights or increase headway with reduced visibility). This affects the credibility of the message and drivers are less likely to comply with advisories if they do not perceive the information as being helpful. There is some existing evidence about driver compliance with these types of messages (mostly from variable speed messages); however, the findings are mixed (Robinson, 2000). In particular, some studies report little to no change in speed behavior, whereas others report more success; these latter instances were often part of a large program that included elements such as increased enforcement. Therefore, it is difficult to attribute the effectiveness of messages to the road information alone. Also, it is uncertain to what extent these findings about reduced speed apply to other recommended actions, such as turning on headlamps. On the one hand, these other actions are typically not associated with enforcement, which could lead to lower compliance than speed reductions. On the other hand, they do not have the same undesirable effects on travel (e.g., longer travel time), so compliance could be better in this regard.

Location information is also important in this type of message if it is not directly implied by the dissemination method. If the hazardous conditions are not near the DMS, location information should be provided if possible. On a DMS, the caution information will be interpreted as being on the road ahead. If it this not the case, then more specific location information should be provided. This is important, because if drivers’ experiences do not match the advisory information, then the driver may perceive this type of information as unreliable and be more likely to disregard this information in the future. See the guideline on communicating geographic extent (Guideline 27) for additional information.

The table below provides a list of existing DMS message examples in use in several states that show different message variations for communicating to drivers that they should alter their driving behavior.

Example DMS messages related to changing driver behavior.
Weather Condition Example Messages
Blowing Dust
  • BLOWING DUST AHEAD SLOW TURN ON LIGHTS
Blowing Snow
  • BLOWING SNOW AHEAD SLOW TURN ON LIGHTS
Bridge or Road Frost
  • BLACK ICE REDUCE SPEED
  • ICE ON BRIDGE SLOW
  • ICE ON ROAD AHEAD SLOW TURN ON LIGHTS
  • WATCH FOR ICE/ICE NEXT ## MILES
Flooding
  • FLOODING AHEAD REDUCE SPEED
  • IF WATER ON RD/TURN AROUND/DON’T DROWN
  • ROAD FLOODED SLOW
  • WATER CROSSING ROAD SLOW
Fog
  • DENSE FOG AHEAD SLOW TURN ON LIGHTS
  • MAX ## MPH IN AREAS OF FOG
  • SPEED LIMIT ## MPH IN AREAS OF FOG
General
  • RIGHT LANES BLOCKED USE LEFT LANE
  • TURN OFF CRUISE CONTROL
High Winds
  • ADVISE NO LIGHT TRAILERS DUE TO STRONG WINDS
  • ADVISE NO LIGHT TRAILERS GUSTS ##+ MPH
  • HIGH WIND ADVISORY/NEXT ## MILES/CAMPERS AND TRAILER/NOT ADVISED
  • HIGH WIND WARNING/NEXT ## MILES/CAMPERS AND TRAILERS/PROHIBITED
  • HIGH WINDS CLOSED TO SEMIS
Moderate to Heavy Snow
  • SNOW BLOWERS AHEAD DO NOT PASS
  • SNOW PLOW AHEAD DO NOT PASS
  • SNOW REMOVAL EQUIPMENT NEXT ## MILES TRUCKS USE RIGHT LANE ONLY
Reduce Speed
  • ## MPH MAX
  • ## MPH MAX SPEED
  • ADVISE ## MPH
  • ADVISE ## MPH MAX
  • ADVISE ## MPH MAX SAFE SPEED
  • ADVISE ## MPH MAX SPEED
  • ADVISE MAX SAFE SPEED ## MPH
  • MAX ## MPH
  • MAX SPEED ## MPH
  • PLEASE SLOW DOWN
  • REDUCE SPEED
  • REDUCE SPEED ## MPH
  • SLOW DOWN
  • SLOW DOWN ## MPH
  • SPEED LIMIT ## MPH ON DOWN GRADE
Trailers
  • ADVISE NO LIGHT OR EMPTY TRAILERS
  • ADVISE NO LIGHT OR EMPTY TRLRS
  • ADVISE NO LIGHT TRAILERS
Wet Roads
  • ADVISE ## MPH WHEN WET
  • AVOID WET ROAD CRASHES

 

Change Driving Behavior: Short Text/Visual Message Examples

For a short message, the key message elements are presented below, with each line corresponding to a DMS message line. For other short text message formats, the message elements are not required to be presented on separate lines; however if space is available, doing so may facilitate message comprehension.

Blank header cell. Message Elements
Baseline Message Baseline Message
Line 1 Weather Descriptor Weather Descriptor
Line 2 Location Location
Line 3 Action Action
Example
  1. BLOWING SNOW
  2. PAST EXIT 12
  3. REDUCE SPEED 35 MPH
  1. DENSE FOG
  2. PAST ROUTE 46
  3. TURN ON LIGHTS

 

2-phase Message with an Audience
Blank header cell. Message Elements
Phase 1 Phase 2
Line 1 Weather Descriptor Audience
Line 2 Location Recommended Action
Line 3 Empty cell. Empty cell.
Example
  1. HIGH WIND ADVISORY
  2. NEXT 4 MILES
  1. CAMPERS / TRAILERS
  2. ADVISE 30 MHP MAX

 

Change Driving Behavior: Example Features or Information for Open Format Text/Visual Messages

Website or other open-format features or content that provide information that supports traveler decision making are shown in the table below.

 

Useful Display Features Information Elements

Route or Area Map (less important)

Screen capture of a route map.

  • Location/extent of problem
  • Color coded major roads or areas affected

Text Information

Driving conditions in text format with indicator icon.

New Mexico 4 Northbound and Southbound from mile marker 33 to mile marker 46.

Difficult driving conditions exist on NM 4, mile marker 33-46 (La Cueva to the Los Alamos County Line). Road is icy in shaded areas. Visibility is good. Please driver with extra caution and reduce your speed.

Last updated: 2009-12-15  13:43:10 MST

 

  • Location of affected area
  • Text description of road weather
  • Recommended action

Camera

Webcam image of a roadway segment.

  • Camera image allows drivers to get a better sense of the severity of the conditions and provides more reason for drivers to change their behavior

 

Change Driving Behavior: Auditory Message Examples

Multiple example auditory messages that are consistent with the auditory message guidelines provided in this report are shown below for this travel decision. The following messages are more suitable for HAR usage than 511 due to their length and references to the radio service.

Example: Advice for Large Vehicles


*Statements in brackets [ ] are optional
Source: HAR Message Development Guide

Example: Leave Greater Headway


*Statements in brackets [ ] are optional
Source: HAR Message Development Guide

 


 

Travel Decision 6: Make Safety-Related Preparations

Introduction

This travel decision applies to situations in which drivers are either required or would be better off making certain preparations before departing or traveling through a specific area. A common example of this situation is when drivers need to put on chains before entering a mountain pass or other snowbound area. However, this can also pertain to a less obvious situation, such as if there is the potential of getting stranded in severe weather conditions or extreme temperatures.

How can travelers use the information?

Available Traveler Actions Travelers who Benefit from this Information Key Information Needs Dissemination Issues
Bring tire chains or high-traction tires Long distance, CVO drivers, and recreational travelers
  • Types of vehicles that must use chains, etc.
  • Information about where drivers can stop
En-route dissemination methods may be less effective for travelers who haven’t brought required equipment
Bring supplies Long distance and recreational travelers
  • That there is a risk of being stranded en-route
  • Conditions are extreme
Mostly applies to dissemination methods available where they can make preparations
  • Cancel trip
  • Take alternative route
Long distance and recreational travelers
  • That there is a risk of being stranded en-route
  • Conditions are extreme
None

 

Discussion

Communicating the need for some vehicles to equip chains or take other related measures is relatively simple. It is common practice in most areas, and phrases like “chains required” etc. are likely to be clearly understood by most drivers familiar with winter conditions. Providing additional information that there is a specific location available to equip chains may also prevent some drivers from stopping at an unintended location to do, however, the likely existence of a chain-up area near an advisory message is also commonly understood by many drivers.

Drivers who do not regularly carry chains and associated equipment require advance warning of chain requirements prior to departure, or early enough to be able to change routes if they believe that it is unsafe or they will not be permitted to continue without chains (see Tutorial 2 for guidance regarding the timing of this information).

Communicating the risk of being stranded or the need to bring supplies is more complicated. Since a route is not closed, drivers are likely to assume that the roads are passable, and some drivers may decide to brave difficult conditions. It is unclear whether or not the recommended action should be to avoid an area in this situation. Once an area is closed the travel decision becomes Travel Decision 7: Cancel Trip. Nevertheless, the information communicated should imply that conditions are severe and that there is a risk of becoming stranded without assistance. Information elements that are consistent with this point include:

Make Safety-Related Preparations: Short Text/Visual Message Examples

For a short message, the key message elements are presented below, with each line corresponding to a DMS message line. For other short text message formats, the message elements are not required to be presented on separate lines; however if space is available, doing so may facilitate message comprehension.

Blank header cell. Message Elements
Baseline Message Baseline Message
Line 1 Action Action
Line 2 Empty cell. Location
Line 3 Location Empty cell.
Example
  1. CARRY CHAINS
  2. OR TRACTION TIRES
  3. 5 MILES AHEAD
  1. CHAINS REQUIRED
  2. ON US 50

 

Other Examples
Blank header cell. Message Elements
Line 1 Weather Descriptor Descriptor
Line 2 Location Location
Line 3 Action Action
Example
  1. EXTREME HEAT
  2. ON SR_190
  3. CARRY WATER
  1. CHAIN CHECK POINT
  2. 1 MILE AHEAD
  3. INSTALL CHAINS NOW

 

Example of a 2-phase Message
Blank header cell. Message Elements
Phase 1 Phase 2
Line 1 Weather Descriptor Audience for Action
Line 2 Location  
Line 3   Action
Example
  1. SNOW ZONE
  2. ON US 50
  1. VEH TOWING OR
  2. Over 10,000 GVW
  3. CHAINS REQUIRED

 

Make Safety-Related Preparations: Example Features or Information for Open Format Text/Visual Messages

Website or other open-format features or content that provide information that supports traveler decision making are shown in the table below.

Useful Display Features Information Elements

Route or Area Map

Screen capture of a route map indicating affected roadway segment.

  • Location/extent of problem
  • Color coded major roads or areas affected

Text Information

Alert - Interstate 70 Eastbound

Chains are required on Interstate 70 Eastbound between mile marker 205 and mile marker 213.

Last updated 2009-12-15  05:35:01 MST

  • Location of affected area
  • Text description of preparations to take
  • Severity information e.g. extreme conditions, risk of stranding, emergency services not operating
  • Prominently displayed text box with attention-grabbing color, text, etc.

 

Make Safety-Related Preparations: Auditory Message Examples

The short text/visual message examples on the previous page provide prescriptive directions to drivers, while the auditory messages below provide informational advisories, along the lines of a public service announcement. Either strength of message is appropriate for either class of dissemination methods. Multiple example HAR or 511 auditory messages that are consistent with the auditory message guidelines provided in this report are shown below for this travel decision. The following messages are more suitable for HAR usage than 511 due to their length and references to the radio service.

Example: Carry Front and Rear Chains, make sure your Vehicle is in Good Operating Condition


*Statements in brackets [ ] are optional
Source: HAR Message Development Guide

Example: Chain Law


*Statements in brackets [ ] are optional
Source: HAR Message Development Guide

Example: If your Vehicle Breaks Down


*Statements in brackets [ ] are optional
Source: HAR Message Development Guide

Example: What to do if Caught in a Blizzard


*Statements in brackets [ ] are optional
Source: HAR Message Development Guide

 


 

Travel Decision 7: Cancel Trip

Introduction

This decision involves abandoning a trip, typically prior to leaving. It is also possible that travelers may cancel a trip en-route under more extreme circumstances, such as if conditions worsen significantly during their trip. The decision to cancel a trip can apply to a variety of scenarios. The most important is if travelers are unable to reach a destination, possibly because the routes are closed or the area is being evacuated. However, certain traveler groups may choose to cancel a trip even if conditions are less severe.

Available Traveler Actions Travelers who Benefit from this Information Key Information Needs Dissemination Issues
Forced trip cancellation All travelers Destination is not reachable Message must be communicated using all available dissemination methods
Voluntary trip cancellation Older travelers, recreational travelers, and travelers with flexible schedules Road weather conditions are challenging None

 

Discussion

The decision to cancel typically has significant impacts on travelers’ schedule (e.g., miss a return flight) and may include financial costs (e.g., cancellation fees, extra accommodation costs). Some travelers may be reluctant to cancel their travel plans because of these schedule and financial costs (see Tutorial 1 for more information on traveler adjustments). Consequently, the message communicating the need to cancel a trip should be unambiguous and convey the severity of the situation, including that travel to a destination is not permitted, not possible, or dangerous.

Some travelers will choose to cancel their travel under less severe conditions. More specifically, if travel to a destination becomes more challenging, some travelers may still cancel their trip, even though their destination is reachable, such as if intended routes are closed, driving requires a high degree of caution, or safety-related preparations are necessary. Trip cancellations of this type are more likely to be made by older drivers, recreational travelers, or those with more flexibility in their schedules. Information about the suitability of providing cancellation information at different trip stages is included in Tutorial 2.

Cancel Trip: Short Text/Visual Message Examples

For a short message, the key message elements are presented below, with each line corresponding to a DMS message line. For other short text message formats, the message elements are not required to be presented on separate lines; however if space is available, doing so may facilitate message comprehension.

Blank header cell. Message Elements
Baseline Message Message Without Recommended Action
Line 1 Weather Descriptor Weather Descriptor (Lanes Closed)
Line 2 Location Location
Line 3 Recommended Action Recommended Action
Example
  1. HEAVY SNOW
  2. DONNER PASS
  3. NO UNNECESSARY TRAVEL
  1. ALL LANES CLOSED
  2. DONNER PASS
  3. TUNE RADIO TO 1190 AM

 

Cancel Trip: Example Features or Information for Open Format Text/Visual Messages

Website or other open-format features or content that provide information that supports traveler decision making are shown in the table below.

Useful Display Features Information Elements

Route or Area Map

 

  • Location/extent of problem
  • Color coded major roads or areas affected

Text Information

  • Prominently displayed text box with attention-grabbing color, text, etc.
  • If very severe, such as a tornado, display text that takes over the page and users (travelers) must dismiss by clicking or other means
  • Location of affected area
  • Severity information i.e. reason for cancelling the trip

Camera

  • Camera image allows drivers to get a better sense of the severity of the conditions and provides a good reason for drivers to trust the information

 

Cancel Trip: Auditory Message Example

This message may be more suitable for HAR than 511 due to its reference to local radio stations. However, the message could easily recommend that drivers listen to 511 instead.

*Statements in brackets [ ] are optional
Source: HAR Message Development Guide

Tutorials

Tutorial 1: Traveler Adjustments based on Weather Information

Tutorial 2: When Travelers Use Weather Information

Tutorial 3: How to Determine which Dissemination Methods Travelers will Use

Tutorial 4: Safety Implications of Road Weather Information

 

Tutorial 1: Traveler Adjustments based on Weather Information

 

Summary: This tutorial provides additional information about the adjustments that travelers may make in response to weather information, in addition to the potential safety implications of these adjustments.

 

Types of adjustments that travelers make

There are many adjustments that travelers can make in response to weather information. Most of the information related to this topic is from studies involving traveler adjustments in response to traffic information, which is likely to be associated with a different set of travel adjustment factors overall. However, some elements, such as expected delays and route changes may be associated with comparable travel decisions related to weather events. In one study of traveler decision making, 40% of travelers were willing to change both departure time and route (35% of these respondents report changing trip based on weather information, vs. 89% for congestion, 86% for traffic reports, 44% for time pressure; Haselkorn & Barfield, 1990). Also, 21% were willing to change their route en-route, 16% were willing to make time, mode, or route changes prior to leaving home, while 23% were unwilling to change departure time. In another study, 60% of travelers reported changing their route or departure time based on radio traffic reports (Khattak, Schofer, & Koppelman, 1992). Finally, a study using travel diaries reported that 37% of trips for which traveler information was consulted resulted in some change in travel behavior (which represented 1% of total trips recorded; Pierce & Lappin, 2003). The most typical changes involved changes to departure time (13%) or route (11%), with only 1% of travelers changing mode.

The brief traveler questionnaire conducted in Task 4 of this project (Richard et al., 2009) provided some information specific to weather-related adjustments. The findings are somewhat different from those found in previous studies because the Task 4 responses were directly tied to a severe weather event that respondents encountered the past year, so they had a specific reason to consult weather information. Consequently, the overall percentage of travelers changing their plans is greater than in previous studies (see Figure E-1 below). Respondents reported changing their travel plans and behaviors in several different ways, with the most common responses being “Drove with more caution” (50%), “Left earlier” (42%), and “Took a different route” (36%). Note that multiple responses were possible, so some travelers may have made more than one of these adjustments during their travel. Overall, travelers seem quite willing to change their plans based on the weather information, a finding which is underscored by the fact that only 11% of respondents reported not changing their travel plans at all.

 

Bar chart indicating frequency of traveler adjustments for the following 7 actions: took a different route, took a different vehicle or type of transportation, drove with extra caution, did not change plans, cancelled or postponed trip, changed departure time, and left earlier.

Figure E-1. Traveler adjustments based on weather information (from the questionnaire given earlier in this project).

 

Safety implications of the adjustments

It is not possible to examine the safety implications of the adjustments in a way that is tied directly into the types of adjustments that travelers make, since there was no related follow up information provided by the surveys covered. However, indirect information is given by the types of weather conditions that require information dissemination to preserve driver safety. In particular, there appear to be just a few general ways in which weather events and corresponding mobility impacts can affect safety. The first is that a traveler can end up at a location that jeopardizes personal safety, such as on a flooded road or where they are at risk of being stranded in harsh conditions (e.g., in a blizzard). The other safety implications relate to increased crash risk stemming from low visibility or low traction conditions.

We did not find data that addressed whether travel adjustments improve or reduce personal safety related to conditions such as being stranded, etc. However, the results of the Task 4 questionnaire from this project indicate that some travelers did make decisions that could have general personal safety benefits in certain situations (e.g., canceling their trip during heavy snow), but without more specific information it is difficult to quantify this benefit. Questionnaire results also provide a slightly better answer regarding driver behavioral adjustments to increased crash risk conditions. In particular, for the subset of 50 respondents who identified “slippery conditions” as a weather impact of concern in a previous question, 60% of these respondents indicated that they “drove with extra caution.” This finding clearly suggests that the travelers surveyed do use weather information to make safer travel decisions in certain crash-risk situations.

 


 

Tutorial 2: When Travelers Use Weather Information

 

Summary:This tutorial provides additional information about when travelers prefer to receive weather information relative to the start of their trip, and how suitable various Dissemination Methods are for providing information at different trip stages.

 

Several sources partially address the question of when travelers use weather information. In particular, one survey found that 15% of motorists sought weather condition information prior to departing (Emmerink, Nijkamp, Rietvald, & Van Ommeren, 1996). This study also found that motorists between the ages of 46-60, in addition to vacation and business travelers, were the most likely to seek out weather condition information prior to leaving. Another study reported the percentage of respondents rating information access as very or extremely important by trip stage, which included 52.3% of travelers having this opinion for before starting their trip, 47.8% for en-route, and 27.7% for stopped on-route (Patten, Pribyl, & Goulias, 2003). In contrast, another road weather survey found that travelers’ preferred information access point depended on the type of traveler (Martin et al., 2000). More specifically, commuters and recreational travelers preferred getting information less than 1 hour before leaving and en-route; “travelers” preferred information at all intervals, with 1-2 days prior and en-route being the most common, and truckers preferred receiving information from up to 3 hours before departing to en-route.

The brief traveler questionnaire from Task 4 of this project also provided some timing information. Table E-3 below shows the percentage of respondents that reported that obtaining weather information at various points during their trip was either “Very Useful” or “Mostly Useful.” In addition to this, the second row provides the same information for just the “Very Useful” response option. Prior to departing and on the road appear to be the most popular times to receive weather information, which is comparable to the findings from Martin et al. (2000).

Table E-3. Partial traveler responses to the most useful time to get weather information (from the questionnaire given earlier in this project).
Blank header cell. During Trip Planning Prior to Leaving At a Stopping Point While Driving
Mostly Useful or Very Useful 63% 78% 57% 70%
Very Useful 37% 52% 30% 39%

 

One limitation of the survey findings is that they lack specific details about the specific travel decisions that travelers are making at various trip stages. This is useful information because trip stage limits the use of some dissemination methods (e.g., internet websites are not typically available while driving), which has implications for how various dissemination methods should be used to communicate certain types of information to travelers. In order to obtain a more detailed picture of how acceptable certain travel decision outcomes might be if they were made at specific stages during a trip, we evaluated each combination of travel decision and trip stage based on suitability of making a specific travel decision at that point (see Table E-4). We used a three-level classification scheme to characterize the “suitability” of a decision outcome based on the following categories:

 

Table E-4. Qualitative ratings describing the likely suitability of making a specific travel decision at various trip stages.
Blank header cell. During Trip Planning Prior to Leaving At a Stopping Point While Driving
Take alternative route? Suitable Suitable Suitable Suitable
Expect delays? Suitable Suitable Suitable Suitable
Drive with caution? Possibly Too Soon Possibly Too Soon Suitable Suitable
Delay departure? Suitable Suitable Too Late Too Late
Cancel Trip? Suitable Suitable or Too Late for Major Trips Suitable or Too Late for Major Trips Too Late
Change Mode? Suitable or Possibly Too Soon Suitable Too Late Too Late
Make special preparations? Suitable or Possibly Too Soon Suitable Too Late Too Late

 

More specific information regarding the timing of traveler information needs relative to the onset of the weather event could not be found. However, one traveler survey did ask about the timing of information needs relative to the start of the trip (Martin et al., 2000). The results of this survey (shown in Figure E-2 below) suggest that the importance of receiving weather information over time relative to the trip start varied as a function of traveler type. In particular, most drivers viewed receiving information less than 1 hour prior to leaving and while en-route as being the most important, but truckers rated 1-3 hours before as the most important and the “traveler” group rated 1-2 days before as among the most important times. These differences are likely to be related to the types of travel adjustments that different types of travelers need to make. One caveat of these findings is that technology use patterns and availability of travel information on various dissemination methods have changed significantly since then (Martin et al., 2000).

Line graph indicating importance in seeking information for the following time periods: 1 to 2 days before leaving, 4 to 12 hours before leaving, 1 to 3 hours before leaving, less than 1 hour before leaving, and while driving. Rated by the following traveler types: trucker, recreational, commuter, traveler, and average for all travelers.

Figure E-2. Graph showing the rated importance of receiving weather information at different times relative to the start of a trip (from Martin et al., 2000).

 

This study also asked about the timing of the information relative to the location of the event. In general, the highest responses were obtained for locations within 50 miles of a weather event or within a specific travel corridor (see Figure E-3).

Line graph indicating importance in seeking information for the following trip distances: more than 300 miles away, 50 to 300 miles away, 1 to 50 miles away, at a specific location, and in a specific corridor. Rated by the following traveler types: trucker, recreational, traveler, and average for all travelers.

Figure E-3. Graph showing the rated importance of receiving weather information at different distances relative to the location of a weather event (from Martin et al., 2000).

 


 

Tutorial 3: How to Determine which Dissemination Methods Travelers will Use

 

Summary:This tutorial provides additional information about the availability of various Dissemination Methods at different trips stages, in addition to information about traveler awareness of and preferences for specific Dissemination Methods.

 

Availability of Dissemination Methods

There does not seem to be any specific data about dissemination method availability or traveler access to disseminations methods during their travel. However, it was possible to analytically determine when most dissemination methods would likely be available to travelers based on how each technology functions. We categorized the dissemination methods in one of four ways based on its likely availability during four basic trip stages. The categories included:

A summary of when most dissemination methods would likely be available to travelers is provided below in Table E-5.

Table E-5. Dissemination method availability for different trip stages.
Dissemination Method During Trip Planning Prior to Leaving At a Stopping Point While Driving
Road Weather Information Kiosks Not Available Not Available Available at Certain Locations Not Available
511 Available Available Available Potential Distraction
GPS/ Personal Electronic Devices Available Available Available Potential Distraction
Cell phone/Text Messaging Available Available Available Potential Distraction
Weather Information Website Available Available Available at Certain Locations Not Available
Commercial Radio Weather Forecasts Available Available Available Available
TV Weather Forecasts Available Available Available at Certain Locations Not Available
HAR Not Available Not Available Available at Certain Locations Available
DMS Not Available Not Available Not Available Available

 

Traveler Awareness of Different Dissemination Methods

Another factor affecting the dissemination methods that travelers use is their awareness of the different methods. If the travelers are unaware of a method, they will not have the option of using it. In the questionnaire from this project, travelers were asked which dissemination methods they were aware of. The results are included in Figure E-4 below.

Bar chart indicating percent of travelers aware of the following dissemination methods: road weather information kiosks, 511, global positions system, cell phone, weather information website, TV or rado weather forecasts, highway advisory radio, and dynamic message signs.

Figure E-4. Percent of travelers aware of each dissemination method.

 

It should be noted that this questionnaire was conducted in Northwestern Washington State and that traveler awareness could be partially a function of the availability of the dissemination methods in that area. However, some strong trends are likely to apply across geographic groups. TV/Radio weather forecasts, HAR, and DMS are all well known methods, whereas kiosks are much less commonly known.

Traveler Preferences for Different Dissemination Methods

Overall, the limited existing research information makes it difficult to understand traveler preferences with a high degree of confidence. A few reports provided some specific findings related to dissemination preferences of select groups, such as business travelers were more likely to change their routes than commuters based on DMS traffic information (Emmerink, et al., 1996; see also Pierce & Lappin, 2003).

One research study examined this issue comprehensively; however, the results are from 2000, and technology use patterns and availability of travel information on various dissemination methods have changed significantly since then (Martin et al., 2000). Results from Martin et al. are shown in Figure E-5 below. Nevertheless, the general pattern, especially for more established dissemination methods, such as DMS/CMS (Changeable Message Sign), HAR, commercial radio/TV and perhaps kiosks, may still hold. With the exception of travelers’ preference for kiosks and truckers’ limited use of TV, preference patterns are similar across traveler types. The other dissemination methods in which differences are observed, such as phone and web, likely have different usage patterns since the survey was conducted.

Line graph indicating ranking of the following preferred dissemination method: pager, kiosks or information desks, CB, email, in-vehicle navigation, phone, internet webpage, TV, highway advisory radio, commercial radio or webcams. Ranked by the following traveler types: trucker, recreational, commuter, traveler, and average for all travelers.

Figure E-5. Dissemination method preference by traveler type (from Martin et al., 2000).

 


 

Tutorial 4: Safety Implications of Road Weather Information

 

Summary:This tutorial provides additional information about how safety/mobility impacts for certain weather events can affect drivers’ personal safety, crash risk, and convenience or schedules. Safety/mobility impacts are generally characterized along these dimensions, which can be useful for prioritizing the importance of specific messages.

 

An important use for road weather information is to preserve traveler safety. Crash data analyses provide a partial indication of which conditions require information. For example, it is clear that certain weather impacts, such as low traction and low visibility play a major role in crashes and fatalities (e.g., Maze, Agarwal, & Burchett, 2005; Pisano, Goodwin, & Rossetti, 2008). Other evidence also suggests that speed reductions are associated with increased crash risk arising from greater speed variability on a roadway (e.g., Hauer, 1971); however, there is some controversy regarding the interpretation of these results (e.g., Davis, 2002). We did not find data showing how weather-related lane obstructions and “reduced traffic capacity” were directly related to crash risk. However, it is not unreasonable to expect that these impacts may increase crash risk in some way, although the relationship may also be less direct (e.g., other related factors such as low traction contribute) or these types of events less common in general.

Crash data do not provide a complete description of the safety impacts and other major ways in which road weather information can help travelers avoid personal safety risks and other undesirable conditions, such as significant unexpected schedule disruptions. In order to obtain a more complete picture of traveler impacts, we used a systematic approach to characterize the general level of risk potentially associated with each mobility impact with regard to personal safety, crash risk, and schedule/convenience impacts. This information can be useful for prioritizing weather impacts. Also, by adding in information about schedule/convenience impacts, it makes it possible to provide an additional basis for prioritizing certain impacts that do not have associated safety consequences. Note that no attempt was made to align the risks from each dimension along the same “severity” scale; however, the personal safety and crash risk consequences are clearly more severe than any of the convenience impacts.

The results of this analysis are presented in Table E-6 below. Two severity levels were used for each dimension, a major or direct risk (solid circle) or a minor/potential risk (empty circle), the latter case representing impacts that are less severe or less likely to occur. Note that for some weather impacts, the associated type of risk was inherent in the definition of the mobility impact (e.g., disruption to transit schedules by definition involves major schedule impacts to travelers dependent on transit). The severity categories were defined as follows:

Table E-6. Potential traveler risks for the basic set of mobility impacts. Information about corresponding weather events and specific impacts on travelers is included in the table to provide additional context when evaluating risks.
Safety/Mobility Impact Associated Conditions Impact on Travelers Personal Safety Risk Crash Risk Convenience / Schedule Impacts
Total Road Closure Blizzard conditions, White-out conditions, Moderate to heavy snow, Sleet or freezing rain, Flooding, Thunderstorms, High winds Requires detour onto alternate routes or delaying travel. Potential impact. No impact. Direct impact.
Reduced traction Blizzard conditions, White-out conditions, Blowing snow, Bridge or road frost, Flurries or light snow, Moderate to heavy snow, Sleet or freezing rain, Moderate to heavy rain Drivers should be more cautious in the affected area. No impact. Direct impact. Potential impact.
Low visibility Blizzard conditions, White-out conditions, Blowing snow, Flurries or light snow, Moderate to heavy snow, Sleet or freezing rain, Moderate to heavy rain, Smoke/mist/fog Drivers should be more cautious in the affected area. No impact. Direct impact. Potential impact.
Lane Obstruction/ Reduced capacity Blizzard conditions, White-out conditions, Blowing snow, Flurries or light snow, Moderate to heavy snow, Sleet or freezing rain, Moderate to heavy rain, Drizzle or light rain, Flooding, Thunderstorms, High winds, Smoke/mist/fog Likely to cause moderate to high levels of traffic congestion in the immediate area. Debris on roadway, lanes unavailable because of snow obstruction/ clearing or partial flooding. Also, vehicles pulling over to side of road, washed out roadways or pavement damage. No impact. Potential impact. Direct impact.
Congestion/ Reduced speed Blizzard conditions, White-out conditions, Blowing snow, Bridge or road frost, Flurries or light snow, Moderate to heavy snow, Sleet or freezing rain, Moderate to heavy rain, Flooding, Smoke/mist/fog Greater speed variability in traffic and loss of roadway capacity. No impact. Potential impact. Potential impact.
TCD Malfunction Blizzard conditions, White-out conditions, Moderate to heavy snow, Sleet or freezing rain, Thunderstorms, High winds Traffic signals are non-operational leading to increased congestion. No impact. No impact. Direct impact.
Unsteady Driving/ High Winds High Winds Drivers (particularly those of larger vehicles/trucks, RVs) should be more cautious in the affected areas. No impact. Direct impact. No impact.
Flooding/ Water Ponding Moderate to heavy rain, Flooding, Thunderstorms Drivers are at risk of being stuck or stranded mid-travel. Potential road closures. Drivers should be more cautious in the immediate area. Direct impact. Potential impact. Direct impact.
Maintenance Vehicles on Road Blizzard conditions, Blowing snow, Bridge or road frost, Extreme cold, Flurries or light snow, Moderate to heavy snow, Sleet or freezing rain, Flooding, Extreme heat Drivers should be more cautious in the affected area. Maintenance vehicles on the road may reduce roadway capacity, leading to increased congestion. No impact. Potential impact. Potential impact.
Transit, Bus Delays/ Stoppage Blizzard conditions, White-out conditions, Blowing snow, Bridge or road frost, Extreme cold, Flurries or light snow, Moderate to heavy snow, Sleet or freezing rain, Moderate to heavy rain, Flooding, Thunderstorms, High winds, Smoke/mist/fog Travel by transit has a higher time cost. No impact. No impact. Direct impact.
Sun Glare Extreme heat, Fair weather Drivers should be more cautious in the affected area. No impact. Potential impact. No impact.
Extreme Temperatures Extreme cold, Extreme heat Drivers should prepare for conditions by bringing along appropriate gear/supplies. Direct impact. No impact. No impact.

 

 

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