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21st Century Operations Using 21st Century Technologies
Table of Contents

Collaboration Across the Road Weather Enterprise: The Pathfinder Project

CHAPTER 3. MAKING THE INVESTMENT CASE FOR ROAD WEATHER FORECASTING AND DECISION SUPPORT SERVICES

THE WEATHER IMPACT ON SAFETY, MOBILITY, AND PRODUCTIVITY

The impacts of weather events on the transportation system have been well analyzed. Adverse weather conditions have been shown to have significant impacts on the safety, mobility, and productivity of transportation system users and roadway operators.

WEATHER IMPACTS ON SAFETY

Over the last ten years, there has been an average of over 5,760,800 vehicle crashes each year. Twenty-two percent (22%) of those crashes-nearly 1,259,000, were weather-related (Figure 4). Weather-related crashes are defined as those crashes that occur in adverse weather (i.e., rain, sleet, snow, fog, severe crosswinds, or blowing snow/sand/debris) or on slick pavement (i.e., wet pavement, snowy/slushy pavement, or icy pavement). On average, nearly 6,000 people were killed and over 445,000 people were injured in weather-related crashes each year.

This chart shows a bar graph of the average number of weather-related crashes, fatalaties, and injuries per year. The top bar shows that 19% of injuries are weather related (over 445,000 people were injured in weather-related crashes each year). The second bar graph shows fatalities; 16% of fatalities are weather-related, totaling 5,897 fatalities per year. The final bar shows that 22% of crashes are weather related- so approximately 1,259,000 weather-related crashes per year.

Figure 4. Chart. Weather-Related Crashes, Fatalities, and Injuries.
(Source: Derived from National Highway Traffic Safety Administration historical data)

Refer to Appendix B to Learn More
Detailed statistics are available in the Weather-Related Crash Statistics Table.

This photo shows a snowy road and background with several large trucks that are on the side of the road. Some of the trucks appear to have crashed into each other.

Figure 5. Photo. A Large Number of Crashes Each Year Are Related to Adverse Weather.
(Source: Wyoming Highway Patrol)

WEATHER IMPACTS ON MOBILITY

Significant roadway capacity reductions can be caused by flooding or by lane obstructions caused by snow accumulation and wind-blown debris. Road closures and access restrictions resulting from hazardous conditions (such as large trucks in high winds) also decrease roadway capacity.

Weather events reduce mobility and travel time reliability through speed reductions and increases in speed variance. Reduced friction due to wet, snow or ice-covered pavement also leads to travel time delays, and start-up delays (i.e., how long it takes a line of cars to start moving from a red light).

Figure 6 illustrates a few percentage ranges that different weather-conditions can have on arterial and freeway travel. Overall, it has been estimated that 23 percent of non-recurring delay on highways across the nation is due to impacts associated with snow, ice, and fog. This amounts to an estimated 544 million vehicle-hours of delay per year.

Figure 6. Graph. Weather-Related Impacts on Arterials and Freeways.
(Source: Derived from National Highway Traffic Safety Administration historical data)

Significant impacts are also felt on freeways in the presence of adverse weather conditions. Figure 6 illustrates a few percentage ranges that different weather-conditions can have on arterial and freeway travel.

Overall, it has been estimated that 23 percent of non-recurring delay on highways across the nation is due to impacts associated with snow, ice, and fog. This amounts to an estimated 544 million vehicle-hours of delay per year.

One important takeaway from Figures 4 and 6 is that there are a range of weather-related impacts to traffic safety and mobility, from minimal to severe. Impact type changes with weather event timing, type, location, etc. The specific impacts for each weather event is an important part of forecasting and decision support services for road system users.

WEATHER IMPACTS ON PRODUCTIVITY

Adverse weather can also increase the operating and maintenance costs of road maintenance agencies, traffic management agencies, emergency management agencies, law enforcement agencies, and commercial vehicle operators. Winter road maintenance activities account for roughly 20 percent of State transportation agency maintenance budgets. Each year, State and local agencies spend more than $2.3 billion on snow and ice control operations.

Each year, trucking companies lose an estimated 32.6 billion vehicle-hours because of weather- related congestion in the nation's top 281 metropolitan areas. The estimated cost of weather- related delay to trucking companies is $3.1 billion annually in the nation's 50 largest cities. The availability of accurate, up-to-date road weather observations that are tailored to the needs of roadway operators together with the decision support tools that place the observation data in a transportation system operations and management context plays a significant role in helping better prepare roadway operators and users of the transportation system for adverse weather conditions. In turn, this approach improves safety, mobility, and productivity.

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