Pisano et al 1
Surface Transportation Safety and Operations: The Impacts of Weather within the Context of Climate Change
By Paul Pisano, Lynette Goodwin, and Andrew Stern
Introduction weather event or from the event’s effect on the pavement. Each year 10 percent of passenger urface transportation is the dominant vehicle crashes occur in rain, snow, or sleet and method of moving people and commerce approximately 13 percent of commercial vehicle in the United States. Services supporting (i.e., large truck) crashes happen in rain, snow, surface transportation require usable sleet, hail, or fog. Roughly 16 percent of infrastructure and effective systems. Primary commercial vehicle crashes occur on wet, snow- highway operational goals—safety, mobility and covered, slushy, or icy pavement each year. The productivity—are affected by environmental combination of adverse weather and poor conditions. Weather acts through visibility pavement conditions contributes to 18 percent of impairments, precipitation, high winds, fatal crashes and 22 percent of injury crashes temperature extremes, and lightning to affect annually (National Center for Statistics and driver capabilities, vehicle maneuverability, Analysis, 2001). pavement friction, and roadway infrastructure. All U.S. residents are exposed to some form The Road Weather Management Program of of weather-related hazards. Nearly 70 percent of the Federal Highway Administration (FHWA) the population and 74 percent of the nation’s has documented operational practices of traffic, roads are located in snowy regions. Over 50 maintenance, and emergency managers percent of U.S. residents have a five percent or employed under various weather threats and the greater chance of being affected by a hurricane weather information needs of travelers. This in any given year. Most hurricane fatalities are paper examines weather impacts on roadways, related to inland flooding after landfall. Nearly operational practices of transportation managers 60 percent of deaths during Hurricane Floyd in and road users, and the weather parameters with 1999 were associated with drowning in vehicles the greatest effects on roadways. Finally, a from fresh water inundation and associated discussion of how possible climate change may flooding. affect these parameters during the next century is presented. Weather affects mobility by reducing traffic speed and volume, increasing travel time delay, Overview of Surface Transportation and decreasing roadway capacity (i.e., maximum Safety and Operations rate at which vehicles can travel). An Iowa State University study concluded that winter Weather impacts roadway safety through storms reduce average freeway speed by roughly exposure to environmental hazards and 16 percent and traffic volume by 29 percent. increased crash risk, either from impacts of a Studies sponsored by the FHWA have found that weather accounts for roughly 12 percent of
The Potential Impacts of Climate Change on Transportation 2 Surface Transportation Safety and Operations: The Impacts of Weather within the Context of Climate Change travel time delay in two metropolitan areas. A (RWIS), advanced traffic management systems nationwide study conducted for FHWA (ATMS), emergency management systems estimated that 23 percent of delay and 11 (EMS), and advanced traveler information percent of capacity reductions resulted from fog, systems (ATIS) as depicted in Figure 1. Vehicle snow and ice in 1999. These weather events detectors and closed circuit television (CCTV) were the most prevalent causes of non-recurrent cameras are components of ATMS used to traffic congestion. monitor traffic conditions. By integrating accurate, timely road weather data into decision- Weather events impact transportation system making processes, transportation managers can productivity by increasing operating and effectively counter weather-related problems maintenance costs and by disrupting access to and disseminate relevant, credible information roadway networks. Nearly 39 percent of road that allows travelers to avoid unsafe conditions operating costs can be attributed to winter or cope with weather effects. maintenance annually. Each year, state and local agencies spend over 2.3 billion dollars on Operational Practices of Maintenance snow and ice control operations and an Managers estimated five billion dollars to repair roadway infrastructure damaged by snow and ice. Maintenance managers obtain surveillance and predictive information to assess the nature and Review of Operational Practices magnitude of an environmental threat. These information resources help managers make Transportation managers utilize three types of decisions about staffing levels, road treatment operational practices to mitigate environmental strategies, the timing of maintenance activities impacts on roadways: advisory, control, and (e.g., crack sealing operations in summer treatment strategies. These mitigation strategies months), and resource management (i.e., are employed in response to various weather personnel, equipment, and materials). threats including fog, rain, snow, ice, high winds, flooding, tornadoes, hurricanes, and Winter road maintenance involves removing avalanches. Advisory strategies provide snow and ice through mobile techniques or fixed information on prevailing and predicted systems. Snow and ice treatment strategies conditions to both managers and motorists to Traffic Emergency influence operational decisions. Control Managers & Managers & Information Maintenance ATMS EMS Service strategies alter the state of roadway devices Managers & Providers & RWIS (e.g., traffic signals, ramp gates) to regulate ATIS roadway capacity and permit or restrict traffic flow. Treatment strategies supply resources to Dynamic National Message Signs & Weather roads (e.g., spreading sand or salt) to minimize Other Roadside Service & or eliminate weather impacts. Devices Vendors
Mesoscale Transportation managers use environmental Environmental Monitoring and traffic data to make decisions about system Networks operation and resource deployment. Weather threat information is typically gathered through surveillance systems that detect and transmit data from roadways to central systems accessed Figure 1. ESS operational applications, showing the by managers. Environmental sensor stations many users of ESS data. (ESS) are deployed along roads across the country to observe atmospheric, pavement, subsurface, water level, and slope stability conditions. Environmental data may be integrated into road weather information systems
The Potential Impacts of Climate Change on Transportation Pisano et al 3 plowing snow, spreading abrasives (e.g., sand) motorists. Increased visibility distance and to improve vehicle traction, and dispensing anti- roadway capacity enhance mobility. icing/deicing chemicals (e.g., salt, magnesium Productivity is improved by preventing vehicles chloride, potassium acetate) to lower the from interfering with winter road maintenance pavement freezing point. In regions with heavy and by minimizing road maintenance costs. snowfall, maintenance managers may erect snow fences adjacent to roads to reduce blowing and Operational Practices of Emergency drifting snow. Managers
Another mitigation strategy involves use of Emergency managers obtain current and slope sensors and avalanche forecasts to predicted weather information through RWIS, minimize landslide and avalanche risks. When a water level monitoring systems, the federal slope becomes unstable due to snow government (e.g. the National Hurricane accumulation or soil saturation, roads in the Center), private companies, the media, and slide path may be closed to allow the controlled various decision support systems. Decision release of an avalanche or landslide. After support systems may present weather data snow, mud and debris are cleared and damaged integrated with population data, topographic infrastructure is repaired the affected route can data, and road and bridge locations, as well as be reopened to traffic. traffic flow data. In response to flooding, tornadoes, hurricanes, wild fires or hazardous In mountainous areas, super-cooled fog can material incidents, emergency managers can persist in valleys for weeks. To improve evacuate vulnerable residents, close threatened roadway visibility and reduce crash risk, roadways and bridges, operate outflow devices managers can employ a fog dispersal treatment to lower water levels, and disseminating strategy. Small amounts of liquid carbon information to the public. Many emergency dioxide are sprayed behind maintenance vehicles management practices require coordination with to encourage precipitation of water droplets in traffic and maintenance managers. the fog. This strategy includes the application of anti-icing chemicals as fog is dispersed to Evacuation management begins with an prevent the precipitate from freezing on road advisory strategy. Emergency managers gather surfaces. weather observations and forecasts to identify hazards, their associated threatened areas, and Maintenance vehicle management practices select a response or mitigation strategy. involve treatment planning, real-time operations Managers may use several control strategies to monitoring, and post-storm analysis. Managers manage traffic on designated evacuation routes. may consult decision support systems to plan the These strategies include opening shoulder lanes most efficient treatment routes, select treatment to traffic, contraflow operations to reverse traffic chemicals, and dispatch crews. Truck-mounted flow in selected freeway lanes, and modified sensor systems facilitate surveillance of road traffic signal timing on arterial routes. conditions and tracking of vehicle status (e.g., truck speed, plow position, material application Emergency managers deploy environmental rate) with automated vehicle location, global sensors (e.g., rain gauges) to monitor positioning system, and geographical precipitation and water level conditions. information system technologies. Surveillance data are used to identify areas that may be significantly impacted by heavy rainfall. Table 1 lists several advisory, control and To prevent or alleviate flooding it may be treatment strategies exploited by maintenance necessary to activate outflow devices to control managers and the resulting effects on roadway the release of water. safety and operations. These strategies improve safety by reducing crash frequency and minimizing risks to field personnel and
The Potential Impacts of Climate Change on Transportation 4 Surface Transportation Safety and Operations: The Impacts of Weather within the Context of Climate Change
Table 1. Operational practices of maintenance managers.
Mitigation Strategies Safety & Operational Effects
S assess nature/magnitude of threat (e.g., impaired Surveillance/Prediction paving, lane obstruction, loss of vehicle stability) S atmosphere (temperature, precipitation, S determine threatened areas/routes visibility, wind) S select appropriate treatment strategy S pavement temperature/condition S mobilize personnel (e.g., prepare/load vehicles) S subsurface temperature/condition Advisory Advisory S determine risks to field personnel (e.g., hypothermia) S water level & flooding S determine risks to roadway infrastructure (e.g., S slope stability (i.e., avalanche/landslide onset) pavement buckling, lane submersion)
Winter Road Maintenance S improve visibility (safety) S conventional snow/ice control S reduce crash risk (safety) (e.g., plow snow, spread sand) S improve vehicle traction (mobility) S apply anti-icing/deicing chemicals S increase roadway capacity (mobility)
Treatment S erect snow fence S minimize treatment costs (productivity)
t Avalanche/Landslide Control S minimize risks to public (safety) S road closure rol & S t minimize risks to field personnel (safety) S release avalanche/landslide S reduce length of road closure (mobility) Con S Treatmen clear roadway & repair damaged infrastructure
Fog Dispersal S reduce crash risk (safety) S spray carbon dioxide into super-cooled fog S increase visibility distance (mobility) S apply anti-icing/deicing chemicals Treatment Maintenance Vehicle Management S route planning S automated vehicle location S minimize treatment costs (productivity) S vehicle system status (e.g., plow blade up) S minimize maintenance costs (productivity) S treatment monitoring (e.g., application rate) Advisory Advisory S post-storm analysis (e.g., plow passes per route)
Some emergency management practices and ensure public safety. Emergency managers must effects on roadway safety and operations are disseminate evacuation orders, road closure and shown in Table 2. Control strategies increase flood information to minimize exposure to roadway mobility by reducing travel time delay hazards. or by maintaining adequate roadway capacity to
The Potential Impacts of Climate Change on Transportation Pisano et al 5
Table 2. Operational practices of emergency managers.
Mitigation Strategies Safety & Operational Effects S assess nature/magnitude of threat (e.g., hurricane storm surge, hail size, wind Surveillance/Prediction speed) S atmosphere (storm track, precipitation, wind) S determine threatened areas/routes S water level & flooding S select appropriate response strategy S traffic volume (e.g., route-specific, state-to- S mobilize personnel (e.g., preposition
Advisory Advisory state) equipment) S travel time S determine risks to roadway infrastructure (e.g., lane submersion, loss of communications) S eliminate field measurements (productivity) Evacuation Management S determine evacuation type/timing (e.g., S minimize risks to public (safety) voluntary, mandatory, phased) S minimize risks to field personnel (safety) S open shoulder lanes S increase roadway capacity (mobility)
Control Control S contraflow (e.g., reverse freeway lanes) S minimize travel time delay (mobility) S modify traffic signal timing
Flood Control S minimize risks to public (safety) S operate outflow devices to induce drainage S minimize risks to field personnel (safety) Control Control
Disseminate Road Weather Information (e.g., storm S minimize risks to public (safety) track, threatened routes, access restrictions) S minimize risks to field personnel (safety) Advisory Advisory
Operational Practices of Traffic Managers or “wet pavement” conditions to identify traffic flow disruptions on freeways. Roadway conditions are monitored from traffic Another control strategy utilized by traffic management centers (TMCs). Most traffic managers is speed management. Speed limits managers access weather forecasts from the are changed based upon the safe travel speed for commercial sector including the media. prevailing visibility, pavement, and traffic Customized weather forecasts are also utilized in conditions. Managers notify drivers of reduced many TMCs and weather data are integrated speed limits via dynamic message signs (DMS) with control software in some TMCs. Based or variable speed limit (VSL) signs. upon weather surveillance or prediction data, managers execute control strategies to manage When travel conditions are unsafe due to traffic flow and advisory strategies to low visibility conditions, lane obstructions, disseminate road weather information. excessive snow accumulation or flooding, managers may restrict access to entire road Traffic signal timing plans may be altered in segments, specified lanes, bridges, all vehicles, adverse weather conditions to accommodate vehicles without required equipment (e.g., tire slower travel speeds on “wet”, “slushy”, chains), or designated vehicle types (e.g., “snowy”, or “icy” roads. Traffic managers may tractor-trailers). Dynamic message signs and modify incident detection software algorithms lane use signs are typically used to inform for “sunny”, “rainy”, “snowy”, “dry pavement” motorists of travel restrictions.
The Potential Impacts of Climate Change on Transportation 6 Surface Transportation Safety and Operations: The Impacts of Weather within the Context of Climate Change
When visibility is reduced by fog or wind- Traffic management practices and associated blown dust, managers may guide vehicles by effects are shown in Table 3. Advisory and illuminating pavement lights embedded in road control strategies improve safety by reducing surfaces or bridge decks to delineate travel traffic speeds and crash risk, and enhance lanes. Traffic and emergency managers also mobility by delineating travel lanes and cooperate to guide vehicle platoons in low minimizing delay. visibility conditions. Patrol vehicles with flashing lights may be used to group traffic into Operational Practices of Travelers or Road platoons. Patrols, at the front and the rear of a Users platoon, lead traffic through affected areas at a safe pace. Transportation managers disseminate road weather information to all road users to
Table 3. Operational practices of traffic managers.
Mitigation Strategies Safety & Operational Effects Surveillance/Prediction S atmosphere (temperature, precipitation, visibility, wind) S assess nature/magnitude of threat (e.g., low S pavement temperature/condition visibility, loss of vehicle traction) S subsurface temperature/condition S determine threatened areas/routes Advisory Advisory S water level & flooding S traffic volume S traffic speed
S reduce speed (safety) Weather-Related Signal Timing S reduce crash risk (safety) (i.e., modify green time, modify cycle length) S Control Control prevent traffic congestion (mobility)
S minimize incident response time (safety) Weather-Related Incident Detection (i.e., modify S reduce risk of secondary incidents (safety) detection algorithms) S Control Control minimize delay (mobility)
Speed Management S S reduce speed & speed variance (safety) determine safe speed S S reduce crash risk (safety) Control Control reduce speed limit
Access Restriction (on threatened routes) S reduce crash risk (safety) S road/bridge/ramp closure S minimize risks to public (safety) S tire controls (e.g., tire chains, snow tires) S minimize risks to field personnel (safety) S S Control Control lane use controls minimize delay due to treatment (mobility) S designated vehicle types (e.g., trucks) S minimize treatment costs (productivity)
Vehicle Guidance (in low visibility conditions) S S delineate travel lanes (mobility) illuminate pavement lights S S reduce crash risk (safety) Control Control lead convoys at safe speed with patrol vehicles
Disseminate Road Weather Information (e.g., access S reduce speed & speed variance (safety) restrictions, safe speed) S reduce crash risk (safety) S roadway warning systems S minimize risks to public (safety) S interactive telephone systems Advisory Advisory S promote uniform traffic flow (mobility) S web sites
The Potential Impacts of Climate Change on Transportation Pisano et al 7 influence their travel decisions. Different types been made in improving short and long range of travelers, or road users, have varying forecasting, there is still a significant gap information needs. In the event of a road between the state-of-the-art and what is needed closure recreational travelers may need alternate to provide a full suite of accurate, high- route information, while commuters familiar resolution meteorological guidance to roadway with their route may not. Passenger vehicle operators and users. drivers are interested in road surface conditions and commercial vehicle operators need Looking into the future, transportation information about road restrictions due to professionals will be able to utilize new subsurface freeze/thaw conditions. Road technologies for decision support. However, weather information allows travelers to make they must also be able to adapt to potential decisions about travel mode, departure time, changes in global climate. This section will rank route selection, vehicle type and equipment, and and discuss those weather parameters that most driving behavior. affect the safety and operations of roadways and how climate change may affect the parameters. Road weather warnings and regulations may be furnished via roadway warning systems, It is apparent in the previous section that telephone systems, web sites, and other there are many weather parameters that affect broadcast media. Roadway warning systems— highway safety and operations. A previous which are typically controlled by traffic effort to describe all the parameters was managers—utilize highway advisory radio completed on behalf of the Office of the Federal transmitters, DMS, VSL signs, and flashing Coordinator for Meteorology. This was done as beacons atop static signs to alert motorists to part of a broader effort to capture the weather hazards. Interactive telephone systems allow information needs for the entire surface motorists to access road weather information transportation community. Since it is not before a trip and while en-route. Many state feasible to examine all these parameters in the departments of transportation (DOTs) provide context of climate change, only those weather general road condition data through toll-free parameters that have significant affects on telephone numbers and via 511, the national maintenance management, emergency traveler information telephone number, which management, traffic management, and road was allocated by the Federal Communications users are identified and prioritized below. Commission in 2001. Travelers may also access Weather parameter rankings are based on tailored road weather information provided by experience and observations of each discipline, private vendors. For example, drivers in rather than extensive analysis. Ranking criteria Minnesota, Montana, North Dakota, and South include area of influence (i.e., portion of the Dakota can dial #7233 (or #SAFE ) to obtain country that is affected by the weather route-specific road condition reports and six- condition), frequency of occurrence (i.e., hour weather forecasts extending 60 miles (or seasonal or year-round effects), impact on one hour) in their direction of travel. Many state roadway operations, and ease of mitigation. DOTs also provide textual and graphical road Table 5 provides a listing of weather parameter weather information on Internet web sites. rankings for each operational area. The sections Mitigation strategies employed by travelers to that follow briefly describe how each parameter improve safety are listed in Table 4. affects roadway operations and safety, and the potential impacts from climate change. Weather Parameters Affecting Safety and Operations
Weather is complex and dynamic. It affects operations and planning for all surface transportation modes. While great strides have
The Potential Impacts of Climate Change on Transportation 8 Surface Transportation Safety and Operations: The Impacts of Weather within the Context of Climate Change
Table 4. Operational practices of travelers or road users.
Mitigation Strategies Safety & Operational Effects
Access Road Weather Information S warnings/regulations via roadway devices S determine mode, route & departure time S tailored road weather data via telephone S select vehicle type & equipment S
Advisory Advisory road weather data posted on web site Make Travel Decisions S defer trip S reduce speed (safety) S prepare vehicle S reduce crash risk (safety) S drive slower Control Control S increase following distance
Table 5. Weather parameters that most affect roadway safety and operations.
Maintenance Emergency Traffic Road User/ Rank Management Management Management Traveler 1 Ice Severe Storms Snow/Ice Snow/Ice
2 Snow Tropical Cyclones Severe Storms Low Visibility
3 Road Temperature Winter Storms Tropical Cyclones Severe Storms
4 Severe Storms Wind (Dispersion Info) Low Visibility Wind (Vehicle Stability)
Potential Climate Change S Average U.S. air temperatures are projected to increase by 3.5 degrees This paper is not a vehicle to discuss the (Fahrenheit) in the spring, by 3.7 validity, magnitude nor duration of projected degrees in the summer, and by 4.0 climate change. Rather, the discussion will take degrees in both the fall and winter. one viewpoint and apply these hypotheses to each weather parameter listed in Table 5. The S The greatest temperature rise is forecast Environmental Protection Agency (EPA), citing to occur over Alaska during the winter studies performed by the National Academy of with an average increase of 10 degrees. Sciences, has indicated that a buildup of greenhouse gases in the Earth’s atmosphere has S During the summer season, the area with hastened a global trend of rising surface the smallest projected temperature rise temperatures. Using the United Kingdom’s extends from the Midwest to the Hadley Centre climate model, the EPA has southern mid Atlantic coast. The areas written reports on the impacts of potential with the largest projected rise are New climate change during the twenty-first century England and the western states. for each state. Table 6 contains a compilation of potential climate change projections with respect S During the winter season, the area with to both air temperature and precipitation. the smallest projected temperature increase extends over the Deep South The seasonal projected temperature changes and Gulf coast states. The area with the for each state by the year 2100 are listed in the largest projected rise (outside of Alaska) temperature columns. From these data, the is along and west of the continental following projections can be made: divide.
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Precipitation models also forecast a general S The average amount of precipitation increase during this century across the nation. across the country is projected to rise by However, unlike temperature, there are a few 10.7 percent in spring, by 14.1 percent locations that are actually projected to have a net in summer, by 16.2 percent during fall decrease in precipitation amounts. These areas and by 19.0 percent during winter. are centered over the intermountain region and the desert southwest during the summer season. S Precipitation projections for Hawaii Additional precipitation related estimates could not be determined due to include: uncertainties associated with
Table 6. Composite of projected climate change by the year 2100.* Source: U.S. Environmental Protection Agency (2002), Global Warming – State Impacts.
Temperature Precipitation Temperature Precipitation State State Sp Su Fa W Sp Su F W Sp Su F W Sp Su F W AL 3 2 4 2 10 15 15 0 MT 4 4 5 5 10 10 10 30 AK 5 5 5 10 10 10 5 5 NE 3 3 4 4 10 10 10 15 AZ 4 5 4 5 20 -10 30 60 NV 4 6 4 6 15 -10 30 40 AR 3 2 3 2 15 25 15 0 NH 4 5 5 5 0 10 10 40 CA 3 5 3 5 30 0 30 40 NJ 4 5 5 4 10 20 20 30 CO 4 6 4 6 10 0 10 40 NM 3 5 4 5 15 -5 5 30 CT 4 4 4 4 10 20 20 40 NY 4 5 5 4 10 20 20 30 DE 3 4 4 4 15 30 15 40 NC 3 2 3 2 15 20 20 15 FL 4 4 4 3 0 0 0 0 ND 4 3 4 4 5 10 15 25 GA 3 2 4 3 10 30 30 10 OH 3 3 4 3 15 25 20 15 HI 3 3 4 3 OK 2 3 3 4 20 20 5 0 ID 4 5 4 5 10 0 10 20 OR 4 5 4 5 5 -5 15 15 IL 3 2 4 3 10 50 30 10 PA 5 3 3 5 10 20 50 20 IN 3 2 4 3 10 30 20 10 RI 4 5 5 4 10 10 15 25 IA 3 2 4 4 10 20 15 10 SC 4 2 4 2 15 20 20 10 KS 2 3 4 4 15 15 15 0 SD 3 3 4 4 10 10 10 20 KY 3 2 4 3 20 30 20 0 TN 3 2 4 3 20 30 20 5 LA 3 3 4 2 0 10 10 0 TX 3 4 4 4 10 10 10 -15 ME 3 5 3 5 0 10 10 30 UT 4 6 4 6 10 -10 30 40 MD 3 4 4 4 10 20 10 30 VT 4 5 5 5 0 10 10 30 MA 4 5 5 4 10 10 15 40 VA 3 3 4 3 20 20 20 20 MI 4 4 4 4 10 20 10 10 WA 4 5 4 5 0 0 0 10 MN 4 3 4 4 0 15 15 15 WV 3 3 4 3 20 25 20 20 MS 3 2 4 2 10 15 15 0 WI 4 3 4 4 0 20 20 20 MO 3 2 3 3 15 40 15 0 WY 4 5 4 6 10 -5 10 30
*Temperature values under are in whole degrees Fahrenheit. Precipitation values represent percentage change from the present climatological norm. Decreases in precipitation are shown in lightly shaded cells. Unknown values are shown in darkly shaded cells.
The Potential Impacts of Climate Change on Transportation 10 Surface Transportation Safety and Operations: The Impacts of Weather within the Context of Climate Change
Pacific Ocean currents and phenomena change scenario presented in the previous such as El Nino. section could impact management practices in the future. S Florida is the only state to have a projection of no change in precipitation Ice Impacts on Maintenance Management amount in any season. The occurrence of ice on the pavement is one of S Winter precipitation amounts are the most hazardous conditions for all road forecast to increase (by over 30 percent) managers and users. Ice can form directly on along the eastern seaboard due to the roadway surfaces (e.g., black ice or frost), or can potential for more frequent nor’easters. fall as precipitation in the form of freezing rain, freezing drizzle or sleet. While the former can Maintenance Management occur anywhere outside of the more tropical climates (e.g., south Florida), the map in Figure The weather parameters with the greatest affects 1 shows that freezing precipitation occurs with on maintenance management are ice, snow, road the highest frequency over the central and upper temperature, and severe storms. The following plains, extending east to New England and south sections describe how these parameters affect over the mid-Atlantic region in the lee of the road maintenance, and how the potential climate Appalachian Mountains. High frequencies can also be seen over portions of the Northwest.
Figure 1. Annual mean number of days with freezing precipitation observed. Source: National Climatic Data Center, 2000.
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With respect to maintenance management, This could increase the frequency, duration, and there are many hazards to roadway safety and amount of ice that occurs particularly from the operations associated with surface icing. Icing mid-Atlantic piedmont north to New England causes a loss of pavement friction, which can and west into the midwestern states. This would reduce maintenance vehicle stability and require that road maintenance agencies in these maneuverability, as well as increased winter regions budget for increased maintenance road maintenance costs. There is also the activities and utilize more effective techniques, potential for lane obstruction and infrastructure such as proactive treatment, to handle potentially damage due to ice accretion on pavement, tree treacherous conditions. limbs, power lines, and communication equipment. Elevated bridges, ramps, and roads Snow Impacts on Maintenance Management out of direct sunlight are at the greatest risk for icy surface conditions. Snow occurs with greater frequency than ice and can cover a larger area in an individual storm. In Climate change projections indicate that in general, the snow threat region only covers general both winter temperatures and about two-thirds of the nation. Figure 2 shows precipitation could increase over the next the mean number of days per year that snowfall century. However, that does not necessarily accumulates to one inch or more. This graphic translate into less ice. Moderation in clearly delineates those regions of the atmospheric temperature could allow continental United States that are affected by precipitation, which would otherwise fall as snowy conditions. The frequency of snowfall is snow, to become freezing rain or sleet. This is a very low over the entire southern tier of states, consequence of relatively warm moisture falling portions of the southwest, and much of the west through colder air masses close to the surface. coast. Snow reduces maintenance vehicle maneuverability, increases winter road treatment costs, and increases the potential for avalanches.
Figure 2. Mean number of days with snowfall of one inch or greater. Source: National Climatic Data Center, 2000.
The Potential Impacts of Climate Change on Transportation 12 Surface Transportation Safety and Operations: The Impacts of Weather within the Context of Climate Change
Long-term climate projections indicate that Severe Storm Impacts on Maintenance mean winter temperatures will increase more Management than in any other season. On average, this could reduce the areal extent and duration of snow Severe convective storms, or thunderstorms, can impacting the country’s roads. It is possible that occur at any time of the year, over the majority the southern fringes of snowy regions shown in of the country, with the highest likelihood of Figure 2 will retreat northward. Warmer ocean occurrence in the Southeast and the Great Plains, temperatures could also provide for more mixed as shown in Figure 3. They typically have a precipitation along the urban corridor from short duration, are somewhat limited in areal Washington, D.C. into New England. However, coverage, and usually occur during warmer the frequency and intensity of nor’easters may months. Though rare, thunderstorms can occur increase and affect interior portions of the mid- in winter. Thunderstorms can produce a plethora Atlantic region into interior New England of dangerous conditions ranging from torrential providing the potential for more disruptions rains, low visibility, lightning, damaging winds, from snow. Under this scenario, maintenance hail, and on rare occasions a tornado or even managers may have to increase budgets for snow blinding snow. These conditions can cause removal in these areas. However, regions infrastructure damage (e.g., lane submersion, ranging from the Carolinas west across the debris on roads) and reduce the productivity of Tennessee Valley into the central plains may see road maintenance crews (e.g., impaired paving). a reduction in winter maintenance costs. The “thunderstorm season” typically extends Road Temperature Impacts on Maintenance from April through the summer and tapers off in Management November. A trend of overall warming could extend this season at both ends. Additionally, Road surface temperatures play a significant role there could be an increase in storm intensity due in determining the effectiveness of winter to warmer daytime temperatures and higher treatment strategies and resulting pavement atmospheric moisture content. This trend could conditions. Dark pavement can efficiently lead to more disruptions of road maintenance absorb daytime solar radiation, potentially activities and necessitate more frequent repair of storing heat overnight or for the beginning of a damaged infrastructure decreasing productivity. precipitation event. However, if pavement temperature falls below freezing in the presence Emergency Management of precipitation or surface moisture, ice can form and pavement friction will be reduced affecting Severe storms, tropical cyclones, winter storms maintenance vehicle operations. In addition, and high winds are the weather parameters with pavement temperature can affect the bonding of the greatest effects on emergency management. ice to road surfaces, which can make treatment The following sections detail how emergency more difficult and more costly. management activities are impacted by these phenomena. An estimation of rising cold season temperatures would act to reduce the total number of days Severe Storms Impacts on Emergency Management with freezing temperatures, particularly along the coastal plain along the Gulf and Southeast Severe storms can produce a number of adverse coasts. However, the temperature rise could conditions year round. Torrential rains can create more frequent freeze/thaw cycles in areas induce roadway flooding. High winds and that currently experience freezing over longer tornadoes can produce swaths of devastation durations. This could cause infrastructure toppling trees and bringing down power lines. damage in the form of buckling, heaving or Large hail can damage property and lightning water main breaks, as well as an increase in the can affect power grids and start fires. Severe number of frost or black ice events.
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Figure 3. Annual mean number of days with thunder observed. Source: National Climatic Data Center, 2000. storms have the highest rank for emergency storm surge and high winds that can undermine management due to their frequency of or submerge roads and damage communications occurrence and high risks of roadway infrastructure. Tornadoes embedded within a infrastructure damage. hurricane can also produce areas of total devastation. While weak tropical systems can Severe convective storms occur primarily during produce significant floods, major structural spring and fall seasons in the months of April damage is usually limited to relatively rare, and May and the months of September and major hurricanes (i.e., Category 3 or higher). October when air masses are under the greatest transition. Projected warming could extend Hurricanes can affect a large area and have these seasons earlier in the spring and later in the significant impacts on emergency management fall (e.g., March through May and September operations, both before and after a landfall. through November). The frequency and Hurricane track, precipitation, and wind speed intensity of these storms may also increase due forecasts factor into management decisions to to warmer temperatures and increased issue evacuation orders and manage traffic on atmospheric moisture. This trend could shift the evacuation routes. The map in Figure 4.4 shows focus of some emergency managers toward the chance (based on climatology) that a tropical activities aimed at handling warm season storms storm or hurricane will affect some portion of and resulting flooding. the eastern U.S. during the hurricane season (June through November). Based on these Tropical Cyclone Impacts on Emergency statistics, both Miami and Cape Hatteras are at Management the highest risk for being affected by a tropical cyclone, at 48 percent. South Florida is at the As coastal populations grow, the likelihood that highest risk of being struck by a major a land falling hurricane will have devastating hurricane, at four percent annually. effects increases. Hurricanes produce coastal
The Potential Impacts of Climate Change on Transportation 14 Surface Transportation Safety and Operations: The Impacts of Weather within the Context of Climate Change
Figure 4. Probability that a named storm (tropical storm or hurricane) will affect any location during the hurricane season. Numbers on the chart represent the probability at that location. Source: Atlantic Oceanographic and Meteorological Laboratory (2002).
According to the United Nation’s S There may be little significant change to Intergovernmental Panel on Climate Change, the total number of tropical cyclones. “[i]ncreasing amounts of anthropogenic greenhouse gases may result in increased S The peak intensity (wind speed) of tropical sea surface temperatures … which could tropical cyclones may increase by five lead to more frequent and intense hurricanes, to 10 percent. typhoons and severe tropical cyclones.” Other experts, such as Houghton et al. 1996 and Increasing population densities combined with Henderson-Sellers et al. 1998, have noted that limited new construction of evacuation routes sea surface temperatures are only one part of the will significantly increase demand and equation necessary for the development of congestion on roadways. Consequently, with a tropical systems and that there is little reason to projection of the same or slightly stronger believe that global warming will significantly tropical cyclones, emergency managers will alter the characteristics of future storms. They need to continue to expend resources on pre- summarize that: storm evacuation planning and post-storm repair or cleanup activities. S There is little evidence to suggest that there will be major changes in where tropical cyclones form or occur.
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Winter Storm Impacts on Emergency Management Traffic Management
Large winter storms, such as the blizzard of Traffic management is affected most 1993 (i.e., the “Storm of the Century”), can significantly by winter weather, severe storms, cause widespread disruption to surface tropical cyclones, and low visibility. The transportation systems. During this blizzard, following sections describe how these weather roadway networks were shut down for days, parameters impact operational practices. impeding emergency response across a large portion of the country east of the Mississippi Snow and Ice Impacts on Traffic Management River. Major winter storms and blizzards can produce significant snow accumulation, blowing Wintry weather of any type can produce snow, reduced visibility, and dangerously low hazardous roadway conditions and can be a wind chill temperatures. The effects of long- major impediment to effective traffic term warming may slightly shift the track of management. Snow, freezing rain, freezing future storms poleward. However, the frequency drizzle and sleet can greatly increase crash risk. of winter storms and nor’easters may increase as Even non-precipitation events such as black ice the warmer subtropical atmosphere and Gulf or roadway frost can greatly reduce vehicle Stream provide energy for storm initiation and traction and maneuverability. Traffic managers growth. The net result is that emergency may employ control strategies (e.g., road, managers from the Rockies east to the mid- bridge, and ramp closures) in an attempt to Atlantic coast may need to expend more mitigate some of these conditions. However, the resources preparing to handle disruptions caused result of wintry precipitation on roadways yields by a higher frequency of these storms. reduced roadway capacity and increased travel time delays. Wind Impacts on Emergency Management As stated in earlier sections, there may be a net Winds can disperse hazardous atmospheric increase in freezing precipitation over certain pollutants, which pose risks to public safety. parts of the country due to projected atmospheric Emergency managers can utilize dispersion warming. This may impact portions of the urban forecasts to predict where a plume of corridor in the northeast. An increase in the particulates will flow, and how pollutants will be frequency of winter storms over the nation’s mid diluted in the air. These forecasts can be used to section and east coast may also increase predict the potential impact of nuclear or snowfall amounts. Traffic managers of the biological chemical releases. Output from future would have to plan for the impacts of dispersion models can be used to identify and these possibilities. delineate evacuation areas, warn communities at risk, and provide information on the level of On the other hand, a possible trend of warming protection required for response personnel may reduce the frequency of occurrence of involved in containment or cleanup activities. A wintry conditions from the Carolinas west across gradual warming trend would promote the the Tennessee Valley and into the southern development of thunderstorms that could contain plains. In these localities, traffic managers strong, gusty winds during a longer period of the would have to deal with a population that is not year. These storms could complicate the accustomed to driving in snow and ice. Traffic prediction of plume trajectories and managers in these situations may need to restrict consequently make evacuation decision-making roadway access more often to minimize crash more difficult. frequency.
The Potential Impacts of Climate Change on Transportation 16 Surface Transportation Safety and Operations: The Impacts of Weather within the Context of Climate Change
Severe Storm Impacts on Traffic Management slightly more intense tropical cyclones in the future. Rain of any intensity can reduce pavement friction, decrease roadway capacity, and increase Low Visibility Impacts on Traffic Management crash risk. On roads that have not had recent precipitation, light rain can mix with pavement In low visibility conditions traffic managers contaminants (e.g., motor oil) decreasing disseminate advisories and regulations (e.g., pavement friction further. Vehicles entering “fog ahead reduce speed”) to travelers to areas of heavy rain can hydroplane or encounter promote more uniform traffic flow, reduce slow or stopped traffic. Heavy rain can produce traffic speeds, and reduce crash risk. In very low visibility, lane submersion, flooded extremely low visibility, traffic managers may underpasses, and damage to roadbeds. Hail and close roads and bridges or coordinate with gusty winds, which can blow trees and power emergency managers to guide traffic through lines down, may also render roads impassible. foggy areas. Lightning can cause disruptions to power, communications, and control systems (e.g., Road Users or Travelers traffic signal system, ramp gates). Travel decisions of road users are impacted An estimate of warming and the contrast in primarily by wintry precipitation, low visibility, temperatures between warmer ocean waters and severe storms, and high winds. The effects of relatively cool land temperatures could lead to these weather parameters are discussed below. the formation of more thunderstorms that reach severe intensity, and extend the thunderstorm Snow and Ice Impacts on Road Users season. In order to prevent frequent congestion and delays, managers may need to utilize The occurrence of wintry precipitation can cause weather-related traffic signal timing and reduced road friction, loss of vehicle disseminate road weather information more maneuverability, travel delays, and increased frequently. crash risk on roadways. In the presence of snow or ice, road users make travel decisions such as Tropical Cyclone Impacts on Traffic Management selecting vehicle type, installing special vehicle equipment (e.g., tire chains), and increasing Tropical cyclones can be a major challenge for following distance. traffic managers, who must coordinate with emergency managers to control cross- Future warming may reduce the amount and jurisdictional evacuation traffic before a frequency of snow across central portions of the hurricane and coordinate with maintenance country and decrease the occurrence of ice managers to identify damaged infrastructure and frequency across portions of the Deep South. In detour traffic in the aftermath. To increase addition, warmer atmospheric temperatures may roadway capacity and traffic flow away from cause mountain snows to occur at higher vulnerable areas, contraflow operations may be elevations. In some areas, the risk of used on major freeway routes to guide vehicles snowstorms and nor’easters could increase due out of designated evacuation areas quickly and to greater temperature differences between the efficiently, and the timing of traffic signals land and ocean. Portions of the interior mid- along major arterial corridors may be changed. Atlantic region into New England may see more After the storm, lanes may be submerged under icing with an increase in coastal storms. water or obstructed by debris and there may be damage to roads, bridges, and other Road temperature also becomes important to infrastructure. Traffic managers must also commercial vehicle operators if their trucks provide advisories and detour information to exceed weight limitations imposed due to threatened populations. Projected warming freeze/thaw cycles beneath roadbeds. This is could lead to the formation of the same or most common for tractor-trailers that traverse
The Potential Impacts of Climate Change on Transportation Pisano et al 17 the northern tier of the nation or travel in Alaska. In these regions, long periods of Wind Impacts on Road Users subsurface freezing or permafrost allow heavy vehicles to travel without damaging the Strong winds can play a major role in vehicle underlying surface. However, during subsurface operation. The buffeting of vehicles may thawing road access to over-weight trucks may decrease their stability and control, particularly be restricted. A projection of warming could in high-profile vehicles. In addition, high winds increase the number of freeze/thaw cycles across blowing across exposed roadways, elevated the northern tier and in Alaska for periods of the expressways or bridges may prevent these winter. vehicles from crossing. Strong winds can blow snow or dust reducing visibility, and reduce fuel Low Visibility Impacts on Road Users economy if blowing opposite the direction of travel. Finally, motorists have to avoid lane Reductions in visibility distance can produce obstructions due to wind-blown debris. variations in travel speed, which greatly increase Estimated warming probably would not have a the risk of chain-reaction crashes. Without significant effect on wind patterns. Those areas information about the safe travel speed, each that typically experience high-sustained winds driver makes his or her own judgment, (such as in the lee of the Rockies or across the contributing to significant speed differences. central plains) would likely continue to experience them. An estimate of future warming would probably not have much effect on fog formation Conclusion in areas that typically experience reduced visibility. There may be a reduction in fog along There is much speculation about how climate the Atlantic and Gulf coasts due to the warmer change will affect the weather over the nation. water temperatures. However, the increased This paper used one scenario from the moisture content of the atmosphere may Environmental Protection Agency as a base to contribute to visibility restrictions elsewhere. project how possible climate changes could Also, there is a possibility that warming could impact surface transportation across the United increase the frequency and intensity of heavy States during the next century. precipitation or wind blown dust, which could also impact visibility distance. With a trend toward warming global temperatures, transportation managers may have Severe Storm Impacts on Road Users to develop and implement mitigation strategies to deal with weather hazards. The following list One of the greatest threats to public safety is summarizes some of the highlights of potential driving a vehicle through moving water of climate change: unknown depth. Each year, many fatalities are attributed to floods from heavy rain, which can S A gradually warming atmosphere may occur from localized storms to major cyclones. increase the frequency of ice (i.e., Prolonged heavy rain can produce flooding in freezing rain and sleet) over portions of underpasses and inundate entire road sections. the Midwest and Northeast as Heavy rain in mountainous terrain may cause a precipitation, heated by warmer ocean sudden rise of water in small streams and creeks temperatures, falls through cold air (known as flash flooding) that can overflow onto masses at the surface. This change may roads. The possibility of landslides, which can have significant effects on mitigation obstruct roadways, also increases during these strategies used by maintenance torrents. Potential warming could increase the managers, traffic managers, and road frequency of heavy rain as warm moist air users. surges north from the Gulf of Mexico and Atlantic Ocean.
The Potential Impacts of Climate Change on Transportation 18 Surface Transportation Safety and Operations: The Impacts of Weather within the Context of Climate Change
S This same warming atmosphere may respond to them. As the climate changes, there produce less snow over portions of the will be a need to continue this trend, modifying Southeast, the Tennessee Valley and the their operations to include the appropriate level lower plains. However, the greater of advisory, control and treatment strategies to difference between land and water limit the weather impacts on roadway safety and temperatures may lead to more winter operations. cyclones that could bring periods of heavy snow, particularly to central and References eastern portions of the nation. These changing snow patterns may produce Atlantic Oceanographic and Meteorological problems in the south as transportation Laboratory (2002) “What Is My Chance of managers and motorists may be less Being Struck by a Tropical Storm or familiar with safe and efficient Hurricane?,” Hurricanes, Typhoons and Tropical operations under these conditions. Cyclones Frequently Asked Questions page, Maintenance and traffic managers http://www.aoml.noaa.gov/hrd/tcfaq/G12.html. across northern climes may have to deal with a higher frequency of winter storms Atlantic Oceanographic and Meteorological or nor’easters. Laboratory (2002) “What May Happen with Tropical Cyclone Activity due to Global S Warming temperatures may change Warming?,” Hurricanes, Typhoons and Tropical freeze/thaw cycles beneath roadways. Cyclones Frequently Asked Questions page, This may induce infrastructure damage http://www.aoml.noaa.gov/hrd/tcfaq/G3.html. such as heaving or buckling. In areas where permafrost has been the norm, Covington, A. (2001) “UDOT Maintenance there may be periods where a thaw may Crews Are Fighting Fog,” Utah Department of necessitate access restrictions for truck Transportation Press Release, traffic. http://www.dot.state.ut.us/public/press_rel/Relea se%2000/Aug%20%20Dec/R_283_00.htm. S The warming atmosphere may lead to a longer and more intense thunderstorm Goodwin, L. and Pisano, P. (2002) “Best season. Transportation managers and Practices for Road Weather Management,” road users will have to cope with the prepared by Mitretek Systems, Inc. for the plethora of conditions that can occur FHWA Road Weather Management Program. with severe storms such as flooding http://www.ops.fhwa.dot.gov/weather/Publicatio rains, gusty winds, lightning and hail. ns/Case%20Studies/BP_RWM.pdf.
S Tropical cyclones may become slightly Henderson-Sellers, A., et al, (1998) “Tropical more intense with projections that the Cyclones and Global Climate Change: A Post- seasonal storm frequency may stay the IPCC Assessment,” Bulletin of the American same. With coastal populations Meteorological Society, 79, 19-38 increasing at a very fast rate, and limited http://www.aoml.noaa.gov/hrd/Landsea/IPCC/. new construction of evacuation routes, traffic and emergency managers will have to plan for better control strategies to manage evacuation traffic.
Today, the impacts of adverse weather on the roadway system are well recognized, and transportation agencies have successfully implemented advanced systems and strategies to
The Potential Impacts of Climate Change on Transportation Pisano et al 19
Houghton, J., et al, (1996) “Contribution of WGI Perrin Jr., J., et al. (2001) “Modifying Signal to the Second Assessment Report of the Timing during Inclement Weather,” University Intergovernmental Panel on Climate Change,” of Utah, http://ops.fhwa.dot.gov/ Climate Change 1995: The Science of Climate Weather/Publications/WxRelatedTiming.pdf. Change, Cambridge University Press, New York, p. 572. Pisano, P. and Goodwin, L. (2002) “Surface Transportation Weather Applications,” FHWA Lawrence, D. (2000) “Innovations in Flood Office of Transportation Operations in Warning: What’s Happening in Dallas?,” 12th cooperation with Mitretek Systems, Inc. Conference and Exposition of the Southwest Association of ALERT Systems, Rice, Jr., et al (2000), “Avalanche Hazard http://www.udfcd.org/saas2000/abstracts/Don% Reduction for Transportation Corridors Using 2Lawrence%20abstract.html. Real-time Detection and Alarms,” University of Utah in cooperation with the Idaho Mitretek Systems (2001) “Surface Transportation Department and the Wyoming Transportation Weather Decision Support Department of Transportation, Requirements (STWDSR): Needs Analysis for http://www.sicop.net/annals-paper%20total.pdf. Traffic and Emergency Management, Preliminary Draft Version 3.0,” prepared for the Spradling, R. (2001) “CHP ‘PACE’ Program,” FHWA Road Weather Management Program. District 10 Press Release, Caltrans, http://www.dot.ca.gov/dist10/pr01.htm. National Center for Statistics and Analysis (2001) “Fatality Analysis Reporting System U.S. DOT Analysis and Information Online (FARS)” and “National Automotive Sampling (2002) “Motor Carrier Management Information System General Estimates System (NASS System (MCMIS) Crash File,” GES),” http://www.nhtsa.dot.gov/ http://ai.volpe.dot.gov/CrashProfile/datasource.a people/ncsa/fars.html. sp.
National Climatic Data Center (2000) “Climate U.S. DOT (2001) “Intelligent Transportation Atlas of the Contiguous United States, Disk 1, System (ITS) Projects Book,” ITS Joint Program Contiguous U.S.,” Product Development Office, p. 285, http://www.itsdocs.fhwa.dot.gov/ Branch, National Oceanic and Atmospheric jpodocs/EDLBrow/@@_01!.pdf. Administration. U.S. Environmental Protection Agency (2002) Owens, M. (2000) “The Advanced “Global Warming – Climate” Transportation Weather Information System http://yosemite.epa.gov/OAR/globalwarming.nsf (ATWIS),” University of North Dakota, /content/ClimateFutureClimateUSClimate.html. http://www.ctre.iastate.edu/pubs/midcon/oens.pd f. U.S. Environmental Protection Agency (2002) “Global Warming – State Impacts,” PDF files PBS&J, (2000) “Southeast United States available for each state at Hurricane Study Technical Memorandum No. 1 http://yosemite.epa.gov/OAR/globalwarming.nsf – Final Report,” http://www.fhwaetis.com. /content/ImpactsStateImpacts.html.
Paul Pisano is the team leader for the Road Weather Management Team in the Federal Highway Administration (FHWA), Office of Transportation Operations. Mr. Pisano has worked in several offices at FHWA over the past 18 years, serving as team leader for the Traffic Safety Research Team at the Turner-Fairbank Highway Research Center before moving to the Office of Transportation Operations. In his current capacity, he is responsible for the program that addresses the impacts of weather on all aspects
The Potential Impacts of Climate Change on Transportation 20 Surface Transportation Safety and Operations: The Impacts of Weather within the Context of Climate Change of the highway system, including winter maintenance. Paul’s educational training is in Civil Engineering, holding Bachelor’s and Master’s degrees from the University of Maryland.
Andrew Stern is a meteorologist and software engineer at Mitretek Systems’ Center for Science and Technology. As a support contractor, his main tasks include providing engineering expertise to the National Weather Service’s (NWS) weather radar program and providing both meteorological and programmatic support to the Federal Highway Administration’s Road Weather Management Program. Prior to coming to Mitretek, Mr. Stern worked as a forecaster for the NWS. He holds a Bachelor’s Degree in meteorology from the Florida State University and a Master’s Degree from the George Washington University.
Lynette C. Goodwin is a Transportation Engineer with experience in research, evaluation, design, and implementation support of Intelligent Transportation Systems (ITS), as well as traffic engineering and transportation planning. She currently supports the Federal Highway Administration Road Weather Management Program and the ITS Joint Program Office. Lynette conducts analysis to determine weather impacts on roadway safety, mobility and productivity; documents best practices used by traffic, maintenance and emergency managers to mitigate the impacts of weather; and supports efforts to document weather information requirements for surface transportation.
The Potential Impacts of Climate Change on Transportation