3
Current Meteorological and Transportation Activities Relevant to Road Weather

Recent and anticipated research and technological advances position the field of road weather for significant steps forward in understanding and capability. Observational capabilities have made great strides, making it possible to obtain a progressively more comprehensive picture of current weather and roadway conditions in recent years. The transportation community is moving in the direction of a road network being operated as a “smart” adaptive system. Accompanying these and other advances in meteorology and transportation are improvements in communications, computational capabilities, and geographic information systems (GIS)—technologies that have clear applications to the road weather problem. In this chapter the committee highlights many current research and development activities that can be applied to road weather research, as well as other existing capabilities that have direct applications to road weather research but have not yet been fully exploited.

OBSERVING AND MODELING THE WEATHER

In Situ Meteorological Observations

Surface weather observations provide benchmark data about atmospheric and surface conditions to the scientific community and a broad spectrum of weather information users. The primary surface-weather-observing system in the United States is the Automated Surface Observing System (ASOS) that has been deployed over the past decade by the Federal Aviation Administration, Department of Defense, and National Oceanic and Atmospheric Administration (NOAA)/National Weather Service (NWS). There are nearly 1,000 ASOS sites across the United States; of those, 569 Federal Aviation Administration–sponsored and 313 NWS-sponsored sites



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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services 3 Current Meteorological and Transportation Activities Relevant to Road Weather Recent and anticipated research and technological advances position the field of road weather for significant steps forward in understanding and capability. Observational capabilities have made great strides, making it possible to obtain a progressively more comprehensive picture of current weather and roadway conditions in recent years. The transportation community is moving in the direction of a road network being operated as a “smart” adaptive system. Accompanying these and other advances in meteorology and transportation are improvements in communications, computational capabilities, and geographic information systems (GIS)—technologies that have clear applications to the road weather problem. In this chapter the committee highlights many current research and development activities that can be applied to road weather research, as well as other existing capabilities that have direct applications to road weather research but have not yet been fully exploited. OBSERVING AND MODELING THE WEATHER In Situ Meteorological Observations Surface weather observations provide benchmark data about atmospheric and surface conditions to the scientific community and a broad spectrum of weather information users. The primary surface-weather-observing system in the United States is the Automated Surface Observing System (ASOS) that has been deployed over the past decade by the Federal Aviation Administration, Department of Defense, and National Oceanic and Atmospheric Administration (NOAA)/National Weather Service (NWS). There are nearly 1,000 ASOS sites across the United States; of those, 569 Federal Aviation Administration–sponsored and 313 NWS-sponsored sites

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services are located at airports throughout the country (http://www1.faa.gov/asos/asosinfo.htm). These data are important in the verification of weather forecasts, in providing real-time weather information to the aviation community, and as input into data assimilation systems for numerical weather prediction. None specifically target the roadway environment. The ASOS is a fully automated system that provides an extensive suite of meteorological observations without human observers. It is sufficiently sophisticated to provide both routine hourly reports and special observations as warranted by changing conditions. The basic data given in each report include sky condition (clouds to 12,000 feet), visibility, present weather, surface pressure, temperature, dewpoint temperature, wind, and liquid precipitation amount. Although not routinely used, the ASOS has the capability to report as often as every five minutes. It was designed to support NWS warning and forecast operations and Federal Aviation Administration aviation weather needs; in addition, the system supports hydrological and climatological programs. Despite its value to many users, the ASOS does not meet all users’ requirements, largely because there are relatively few stations and because their observations are representative only of a small area near the site. As a result various user groups have developed and installed their own specialized surface-observing systems. Representativeness of surface observations is particularly important to the roadway environment, where minor differences in the physical environment (e.g., slope and exposure) lead to dramatically different effects. Although the ASOS provides useful data, it was never intended to be used to characterize the roadway environment; therefore, additional networks that target the roadway environment are needed. Another very similar system is the Automated Weather Observing System (AWOS), which is a suite of sensors designed to collect and disseminate weather data primarily to assist the aviation community. The systems are classified as federal, which are owned and maintained by the Federal Aviation Administration, and nonfederal, which are owned and maintained by state, local, and private organizations. There are six different AWOS sensor arrays. The most basic array of sensors report wind speed (including gusts) and direction, temperature, dewpoint temperature, pressure, and density. The other five arrays build off this basic suite by reporting such additional parameters as visibility, sky condition, present weather, or lightning detection. Over 600 AWOS sites exist throughout the United States (http://www1.faa.gov/asos/awosinfo.htm). As with the ASOS, the AWOS was not deployed to observe the roadway environment, although its data are useful for synoptic weather observing and forecasting purposes.

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services The need for high-density observations is not unique to highway operations. Numerous mesoscale observing networks have been deployed around the United States, including the Oklahoma Mesonet (Horel et al., 2002b) and the Atmospheric Radiation Measurement Cloud and Radiation Testbed site (Stokes and Schwartz, 1994) in the central Plains. MesoWest, a heterogeneous collection of over 70 networks providing more than 2,800 observations, was assembled over the western United States in part to support the 2002 Winter Olympics in Salt Lake City, Utah (Horel et al., 2002a, b). These, as well as other networks operated by federal, state, or local governments or private entities, have been installed to serve special needs: most often meteorological research, agricultural operations, or air quality monitoring. In addition to the surface-based observations, in situ weather data are routinely collected on commercial aircraft as part of the Aircraft Communication Addressing and Reporting System (ACARS) (Moninger et al., 2003). This program is the largest and longest-running data collection effort developed specifically for constantly moving platforms; it provides 80,000 reports a day with critical information about temperature, humidity, and wind in the atmosphere up to 15 km altitude (Figure 3-1). A similar system for FIGURE 3-1 Locations of observations obtained from aircraft and collected in the Aircraft Communication Addressing and Reporting System (ACARS) for a 3.5-hour period in March 2000. The data are color-coded to reflect the height where they were obtained. SOURCE: NOAA.

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services FIGURE 3-2 Daily streamflow conditions for January 21, 2004. Black indicates a new record high for the day, blue indicates flow greater than the 90th percentile, light blue indicates flow between the 75th and 89th percentile, green indicates flow between the 25th and 74th percentile, orange indicates flow between the 10th and 24th percentile, dark red indicates flow less than the 10th percentile, and bright red indicates a new record low for the day. SOURCE: U.S. Geological Survey. observing the roadway environment using vehicle probes is described in “Observing and Modeling the Roadway Environment” later in this chapter. In addition to in situ sensors that monitor meteorological conditions, there are networks that monitor responses to those conditions. Of greatest concern to the roadway environment is heavy precipitation, which can lead to flash flooding. The U.S. Geological Survey operates a nationwide network of gauges to measure streamflow, data that are available in near realtime (Figure 3-2). These data can be used—as in Louisiana’s HydroWatch system (Wolshon and Levitan, 2002)—to gauge flood threat and if correlated with road elevation information, to determine when roads may become submerged. Remote-Sensing Observations Instruments that can observe atmospheric or land surface properties remotely offer ways to extend the spatial coverage of the observation net-

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services work. These instruments can be “active,” in which case they send out a pulse of electromagnetic energy and then use the reflected signal to determine characteristics of the atmosphere, or they can be “passive,” in which case they measure radiation emitted naturally by the atmosphere. Radar (Figure 3-3) is a widely used active remote-sensing technique that provides near real-time observations of the atmosphere under both clear-air and precipitating conditions. The deployment in the 1990s of Next Generation Weather Radar (NEXRAD) has provided the United States with a national remote-sensing network using Doppler radars (NRC, 2002). The radars provide nearly continuous monitoring of precipitating, severe weather complexes, and, when operating in clear-air mode, of nonmeteorological echoes (e.g., insects, dust), which can indicate wind speed and direction. NEXRAD incorporates sophisticated signal processing to sense the Doppler shift in the echoes returned from FIGURE 3-3 A Doppler Radar. SOURCE: Bob Baron, Baron Services.

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services moving scatterers, thereby providing information on the wind field in the observed region. A new “volume scan” of a three-dimensional region around each radar is available every five to six minutes. Efforts are currently under way to (1) integrate other radars producing a weather signal (particularly those operated by the Federal Aviation Administration) in order to enhance coverage and provide redundancy; (2) upgrade the radar to improve its capabilities for sensing precipitation; and (3) make higher-resolution radar data and derived products more generally available. Additionally, dual-polarization radars (i.e., radars that transmit and receive both horizontal and vertical polarizations) have the potential to aid weather observation and prediction by distinguishing between rain and hail and by identifying the precipitation type in winter storms. These radars could be installed in the national radar network within 5 to 10 years. Also in development are high-resolution national composites or mosaics, which will merge all available radar data into one database for the nation. Current regulations prevent NEXRADs from being operated at beam elevations below 0.5°, limiting the extent to which the radar can see very low elevations. Despite this institutional limitation, the NEXRAD is able to track precipitation, determine winds, and detect other phenomena such as blowing dust; thus it has the potential to be applied effectively to improving road weather information products (Mahoney and Meyers, 2003). Profilers are vertically pointing Doppler radars that collect temperature, moisture, or wind data through the atmosphere. For example, 400-MHz-band wind profilers are able to detect winds directly above the profiler site at heights from about 500 m to 16 km, making them useful for weather forecasting. Additionally, there are 900-MHz-band radar wind profilers that can be combined with Doppler sodars to obtain boundary layer winds down to about 30 m. When wind profilers are coupled with radio acoustic sounding systems (RASS), temperature profiles down to approximately 1 km also can be obtained. A sequence of wind profilers for Conway, Missouri, is shown in Figure 3-4. Though profilers are a reliable, proven technology, there is not a dense network of these observations, and the lack of data at lower levels and the coarse vertical resolution limit their usefulness for near-surface applications (NRC, 2003c). Figure 3-5 shows the location of wind profiler sites in the contiguous United States. Recent advances in wind profiler technology have created the capability to monitor the altitude of the melting level in winter storms. Observations from instruments on satellite platforms that actively and passively sense visible, infrared, and microwave radiation now routinely provide data that can be processed for information on the distribution of

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services FIGURE 3-4 Hourly wind profiler observations over Conway, Missouri, on July 31, 2003. SOURCE: NOAA. atmospheric and surface parameters in both the horizontal (imagers) and vertical (sounders). One widely used satellite observation is water vapor imagery from NOAA’s Geostationary Operational Environmental Satellite (GOES); such imagery often is animated to show the movement, development, and dissipation of large-scale weather systems. Satellite data provide excellent spatial coverage, filling in observations of weather conditions between surface-observing systems, and can be frequently updated. Civilian satellite sensor data are limited, however, in that they cannot resolve features the size of highways. Several satellite-based sensing systems under development hold promise for applications to the roadway environment. Wind Index (WINDEX), an experimental GOES product, estimates the highest wind gusts that would occur if showers or thunderstorms were to develop. WINDEX is produced hourly from the sounder product and plotted on a satellite image. Originally developed for aviation operations, it could be used by surface transportation managers as an outlook to the potential occurrence of high wind and blowing dust associated with showers and thunderstorms, thus activating

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services FIGURE 3-5 Distribution of wind profiler and radio acoustic sounding systems (RASS) sites in the contiguous United States. The star represents a wind profiler coupled with a RASS; the circle represents a wind profiler only; and the triangle represents a RASS only. The symbol colors represent data availability which vary daily. SOURCE: NOAA’s Forecast Systems Laboratory. cautions on dynamic message signs. On average, WINDEX estimates are within 5 knots of observed maximum surface wind gusts. A fog and low cloud imaging capability, developed in support of aviation operations, analyzes different wavelengths of infrared radiation and using the differences, identifies low clouds and fog (Figure 3-6). Distinguishing between low clouds and fog is a challenging problem because there is a strong dependence on the underlying topography. Merging the satellite information with three-dimensional GIS data could lead to enhanced capabilities for distinguishing between low clouds and fog. The Hydro-Estimator, one of the oldest quantitative derived satellite products, estimates precipitation down to the county level and, when combined with three-dimensional GIS data, could assist in anticipating prob-

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services FIGURE 3-6 Fog location (a) and depth (b) over San Francisco Bay. SOURCE: NOAA. lems in flash-flood-prone areas (Figure 3-7). These data are being incorporated in hydrological prediction models to forecast river and stream flows. Monitoring the vast tropical oceans is a job that satellites do very well. GOES allows large regions of the tropical ocean to be continuously monitored throughout the life of a tropical cyclone, from genesis to dissipation. When in situ monitoring of tropical cyclones1 by aircraft, ocean buoys, or ship reports is not available, minimum pressure and maximum winds can be estimated in a variety of ways using remotely sensed data. Most commonly, tropical cyclone intensity is estimated from cloud patterns and temperatures using visible and infrared satellite imagery. Other instruments, such as the Advanced Microwave Sounding Unit, the Special Sensor Microwave/Imager, and scatterometers, are being used to estimate intensity and wind structure. GOES data provide frequent updates of track and intensity changes as the tropical cyclone moves toward land, contributing to substantial improvements in the forecast of land-falling tropical storms and hurricanes. A new product, the Tropical Rainfall Potential, utilizes both GOES 1   “Tropical cyclone” is the generic term for all tropical low-pressure systems, including tropical depressions, tropical storms, and hurricanes. A tropical cyclone is named when it reaches tropical storm intensity (maximum sustained winds of 39–73 miles per hour), and it becomes a hurricane when reaching maximum sustained winds of 74 miles per hour or greater.

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services FIGURE 3-7 Satellite and radar precipitation estimates from tropical storm Allison: (a) in situ observations from rain gauges and (b) satellite observations from the Hydro-Estimator. Each panel shows total rainfall in inches for the 24 hour period ending on June 6, 2001 at 12:00 UTC. SOURCE: National Aeronautics and Space Administration. and microwave data from polar satellites as well as the storm track forecast to estimate the potential rainfall of a system when it makes landfall. Ideally, data from satellites, radars, and rain gauges should be combined to provide the best estimate of rainfall. Geostationary and polar satellites can also provide other variables of potential relevance to the roadway environment. GOES sensors can monitor land temperature changes under clear sky conditions. Other sensors on recent satellite series (e.g., the Polar Orbiting Environmental Satellite, Earth Observation Satellites, Defense Meteorological Satellite Program) can monitor a variety of surface properties daily to weekly. For instance, the Normalized Difference Vegetation Index is used to monitor vegetation greenness and health; these data can be correlated with blowing dust, which limits visibility, and they could be important for modeling the moisture flux of the roadway environment. A variation of the satellite vegetation product uses current weather information, particularly precipitation and temperature data, in a new experimental fire risk product that might provide additional insights for roadway managers regarding the spread and impact a wildfire might have on surface transportation and evacuation operations. GOES near-infrared data can be used to monitor the fire locations as well as the coverage and changes in smoke plumes (Figure 3-8).

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services FIGURE 3-8 (a) Smoke from large fires in Montana and Idaho, August 22, 2000; (b) Narrow plumes from fires in Louisiana and Texas, September 5, 2000. SOURCE: National Aeronautics and Space Administration. More than a hundred new sensors under development will be installed on satellite platforms within the next decade. Improved resolution, more frequent imaging, hyperspectral imaging, and new sounders are slated for launches by U.S. and global satellite partners. These sensors will provide new and improved observations of the atmosphere, including variables such as soil wetness, snow water equivalence, and smoke and aerosol detection over land. Examination of and development of applications from today’s satellite-based observations will prepare the surface transportation community to maximize the use of these data now and in the future. Modeling the Atmosphere Numerical weather prediction is the foundation of modern weather forecasting. Today’s state-of-the-science models are run multiple times per day and on horizontal grids with spacing as fine as just a few kilometers. The NWS currently is running the Eta model on a 12-km horizontal grid out to 3.5 days (84 hours) four times per day (http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/). Most forecast models are “full-physics” versions that provide explicit predictions of temperature, dewpoint temperature, wind, and precipitation. Forecasts for related sensible weather parameters, such as visibility and clouds, are generally derived by statistically post-

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services FIGURE 3-20 Causes of nonrecurring traffic delay. SOURCE: John Wolf, California Department of Transportation. mizes the average number of stops per vehicle, thereby improving the safety and efficiency of the roadways. Once the road weather conditions improve, traffic signal operations are restored to normal. Other control strategies used by traffic managers during inclement weather include speed management, land or vehicle restrictions, and guidance techniques (Pisano et al., 2002). Driver speed is managed based on the visibility, pavement, and traffic conditions by reducing speed limits to a safer velocity that is conveyed to drivers via dynamic message signs or variable speed limit signs. Traffic managers may also restrict access to road segments, lanes, or bridges or restrict the type of vehicles (e.g., tractor-trailers, vehicles without tire chains) allowed on portions of the roadway when visibility is low or lanes are obstructed due to snow or flooding. Finally, when visibility is poor, traffic managers may use pavement lights embedded in the road surface to delineate travel lanes, or they may use patrol vehicles with flashing lights to lead drivers safely through affected areas.

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services Although these traffic management tactics can greatly improve driver safety during inclement weather or poor road conditions, they are reactive rather than proactive. Better system performance relies on deployment of transportation management systems that account for weather (Nelson, 2002). Most authorities are quite familiar with the range of weather events that can affect their roadways, but only some organizations have mitigation strategies in place to exploit the use of advanced weather information. Emergency Management Major advances in intelligent transportation systems, weather research, vehicle technologies, electronics, and geographic information systems have created tremendous opportunities for improved emergency management practices for the transportation industry. Although emergency response to weather disasters such as tornadoes has been studied to some extent (Goodwin, 2003a), responding to tropical cyclones has received the most attention from the surface transportation research community because they call for massive evacuations relying primarily on highways. Efforts to address surface transportation implications of other weather-related emergencies are less developed and are not discussed in detail here. The intensity of tropical cyclones and the damage they inflict when making landfall create considerable transportation-related problems (Figure 3-21). From the 1970s through the early 1990s hurricane activity was moderate in the Atlantic basin (Gray et al., 1993), and there was a concurrent explosion in population along the Gulf and East Coast regions of the United States (Pielke and Landsea, 1998). The rapidly growing coastal population and increased tropical cyclone activity necessitated thorough, efficient evacuation plans. The United States is among a small number of countries that rely on mass evacuations to protect their population during hurricanes. Evacuations used to be the responsibility of emergency management and law enforcement officials, but after the major traffic jams associated with Hurricane Georges in 1998 and Hurricane Floyd in 1999, the professional transportation community took a more active role in the planning, management, and operation of evacuations (Wolshon et al., 2001). These two hurricanes highlighted the need for better planning and coordination, increased evacuation route capacity, and better information exchange. The most important aspects of effective hurricane evacuations are advance warning times and access to transportation; this is especially important because the majority of deaths associated with hurricanes result from inland flooding, and drivers are particularly susceptible. Track and intensity

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services FIGURE 3-21 Flooding during Hurricane Floyd, September, 1999. SOURCE: Louisiana State University Hurricane Center. forecasts from the NOAA/NWS National Hurricane Center are used to monitor a hurricane and determine if evacuation is necessary. This decision usually is based on the hurricane’s intensity (Table 3-2), size, track, and speed. A hurricane technically makes landfall when its eyewall—the most intense region of the storm—reaches land, but tropical storm- or hurricaneforce winds can occur much earlier when strong outer rainbands reach land. Timing is of the essence when allowing for configuration of all traffic control elements on evacuation routes, the actual evacuation process, clearing of all routes, and removal of evacuation-coordination personnel once deteriorating conditions commence. According to Wolshon et al. (2001), medium-size cities need at least 12 hours to initiate and complete evacuation, but larger cities with limited evacuation routes, such as New Orleans, may require up to 72 hours. The preferred minimum evacuation-advance-notification times of several coastal states is given in Table 3-3. Although initiating evacuation earlier gives more time for people to leave, it also gives more time for the track of a hurricane to change; the average 24-hour track error during 1992–2001 was 93 miles (Franklin et al., 2003). Several technologies and procedures have been explored and, to some extent, adopted to improve the efficiency of evacuation procedures. One issue that often has been overlooked is the interference of work zones and

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services TABLE 3-2 The Saffir-Simpson Hurricane Scale, which Rates a Hurricane Based on Its Maximum Sustained Winds Category Winds (mph) Effects 1 74-95 No real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery, and trees. Some coastal road flooding and minor pier damage. 2 96-110 Some roofing material, door, and window damage to buildings. Considerable damage to vegetation, mobile homes, and piers. Coastal and low-lying escape routes flood 2 to 4 hours before arrival of center. Small craft in unprotected anchorages break moorings. 3 111-130 Some structural damage to small residences and utility buildings with a minor amount of curtainwall failures. Mobile homes are destroyed. Flooding near the coast destroys smaller structures, with larger structures damaged by floating debris. Terrain continuously lower than 5 feet above sea level may be flooded inland 8 miles or more. 4 131-155 More extensive curtainwall failures with some complete roof structure failure on small residences. Major erosion of beaches. Major damage to lower floors of structures near the shore. Terrain continuously lower than 10 feet above sea level may be flooded, requiring massive evacuation of residential areas inland as far as 6 miles. 5 > 155 Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. Major damage to lower floors of all structures located less than 15 feet above sea level and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5 to 10 miles of the shoreline may be required.   SOURCE: http://www.aoml.noaa.gov/general/lib/laescae.html.

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services TABLE 3-3 Preferred Minimum Evacuation-Advance-Notification Times (in hours) for Several Southern and Eastern Coast States   Hurricane Category State 1 2 3 4 5 Massachusetts 9 9 12 12 1 Rhode Island 12-24 12-24 12-24 12-24 12-24 Maryland 20 20 20 20 20 Virginia 12 18 24 27 27 South Carolina 24 24 32 32 32 Georgia 24-36 24-36 24-36 24-36 24-36 Mississippi 12 24 24 48 48 Louisiana 24 48 72 72 72   SOURCE: Wolshon et al., 2001. the congestion caused by lane closures or detours. Most construction occurs during the summer, coinciding with the Atlantic tropical cyclone season, which extends from June 1 through November 30. To minimize this problem, some departments of transportation have included special provisions in construction contracts that require contractors to cease activities, clear their equipment, and reopen lanes in the event of an evacuation. Other states simply do not allow construction that reduces normal traffic capacity. ITS information is being used increasingly during evacuations to collect and disseminate real-time data about traffic flow rates, road closures, weather conditions, and availability of alternate routes. Traffic cameras can be used to give visual confirmation of evacuation conditions. Highway advisory radio and dynamic messaging signs are being used to communicate important information to evacuees in a timely manner. Such information may include shelter locations, alternate evacuation routes, congestion and accident information, and services such as lodging and rest areas. The main limitation of such systems is that they most often exist in urban areas, whereas the majority of evacuation routes are in rural regions (Wolshon et al., 2001). Since the traffic jams caused by hurricanes Georges and Floyd in 1998 and 1999, respectively, an evacuation procedure called “contraflow,” which reverses one or more lanes of traffic flow to increase capacity, has been explored (Figure 3-22). There are four variants to this contraflow technique, assuming two inbound and two outbound lanes divided by a median (e.g., an interstate, a four-lane divided highway): (1) all lanes reversed; (2) one

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services FIGURE 3-22 Contraflow along I-26 near Charleston, South Carolina, during reentry after Hurricane Floyd in September 1999. SOURCE: South Carolina Department of Transportation. lane reversed and one lane with inbound flow for emergency service; (3) one lane reversed and one lane for normal inbound flow; and (4) one lane reversed and the use of left shoulder of outbound lanes. The reversal of all lanes increases capacity by about 70 percent. Reversing just one lane and leaving the other for either emergency or regular inbound flow increases capacity by 30 percent, but it also increases the potential for accidents. Usage of the left shoulder for extra outbound traffic improves capacity by only 8 percent, and it has the potential for the greatest problems due to lack of pavement suitable for driving and the inconsistency of shoulder widths (Wolshon et al., 2001). There currently are no standards or guidelines for designing contraflow operations. Typically a median is used for the crossover, but it also can take place at a freeway interchange. The decision about when to use contraflow, under what conditions, for how long, and how to communicate the information to the public usually falls on state governors, although they often task local law enforcement and state departments of transportation to manage the operations. The main criteria for deciding whether to use contraflow

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services procedures are the characteristics of the hurricane (i.e., size, intensity, track, track speed), traffic volume, setup time, time of day, land use, and traffic conditions and patterns. By the time barricades are erected, traffic is cleared, and law enforcement is positioned, it can take 12 hours or more just to prepare a contraflow. Although contraflow operations are beneficial in providing increased evacuation capacity, the procedure can be inconvenient, confusing, unsafe, labor intensive, and difficult to enforce. Overall, the costversus-benefits remains unknown. Several research efforts will be necessary for effective emergency management of the roadway environment. These include development of realtime detailed evacuation models that simulate actual roadway operations and combine various types of weather data with transportation and geographic data in one standardized display. Accomplishing this will require relationships between the meteorological and transportation researchers and practitioners to be further developed. In addition, these research efforts must be combined with tools for communicating reliable real-time information to the public, more complete data regarding the real-time operation of the transportation system, and improved mechanisms for sharing data and information. Institutional issues must also be addressed, as many different agencies and jurisdictions are usually involved in emergency management. Roadway Design and Construction Designers and builders of roadways must account for weather in their daily operations and long-term planning. For example, air temperature, humidity, wind, and precipitation play a fundamental role in the drying, hardening, and shaping of both concrete and asphalt. Ideally roads should be strong enough to carry loads, be durable and have low permeability to resist water and chemical penetration, be resistant to cracks and chemicals to prevent deterioration, and be aesthetically pleasing. However, for concrete, hot weather (75 to 100°F) can (1) accelerate setting, which inhibits a smooth finish; (2) increase the concrete temperature, which reduces the long-term strength of the pavement; and (3) increase the rate of hydration, which causes shrinkage and cracks. On the other hand, cold weather (< 40°F) can slow hydration, which retards hardening and strengthening (Smith, 2003). For asphalt the surface temperature before the mix is laid is critical, with higher surface temperatures (> 55°F) required for thinner slabs and cooler temperatures (> 35°F) allowed for thicker slabs (Spaid, 2004). Precipitation of any kind or amount can be very detrimental to concrete or asphalt construction. Liquid precipitation can create an imbalance in the

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services FIGURE 3-23 Schematic showing how temperature and moisture differentials above and below a concrete slab can cause it to curl up or down. SOURCE: Harold Smith, Center for Transportation Research and Education, Iowa State University. moisture load, while hail can damage the surface, especially during the first 4 to 6 hours of placement. For asphalt, rain can wash away the tack coat placed on the surface before the mix is laid, leading to costly cleanup and replacement. Differences in temperature and moisture on either side of a concrete slab can cause it to curl (Figure 3-23). The effect of weather on roadway construction goes beyond physical damage; it has an economic impact as well. Money can be lost even before paving begins if weather prohibits concrete or asphalt from being poured. For instance, concrete mixture can remain in the truck for only 30 minutes, so the mixture may have to be dumped if unexpected high winds or precipitation occurs. Inaccurately forecast or sudden storms also can result in lost wages for idle paving crews. Once the pavement has been placed, hail or rain can damage a slab to the extent that total removal ($8 to $10 per square yard) and reconstruction ($25 per square yard) are warranted. If only superficial damage is done, the concrete can be diamond grinded ($4 to $8 per

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services square yard) to restore its surface (Smith, 2003). Even with notice of inclement weather there is some loss in production as work is suspended and the pavement is covered to minimize damage, then uncovered to resume paving. Despite such efforts, surface damage still may ensue. Ideally contractors want better than 85 percent accuracy with a minimum 0.5- to 2.0-hour notice for at least a 2 km2 or smaller grid (Smith, 2003). Most construction supervisors obtain weather information from the NWS, free Web-based services, and in some cases, specialized forecasts produced by private sector companies. However, the information often is not as timely or on as fine a scale as is needed by the roadway construction community. Decision support tools that meet the needs of the roadway industry are starting to be developed; for example, High Performance Paving is a prediction tool specific to the roadway construction community that uses temperature, wind, and humidity information to predict optimum paving windows and the impacts of adverse weather on roadway construction (see http://www.hiperpav.com). The weather information needs of the construction community were recognized by the inclusion of the Maintenance and Construction Operations user service in the National ITS Architecture in 2002. INTELLIGENT TRANSPORTATION SYSTEMS A major effort of the last decade by the surface transportation community has been to design and implement ITS. These systems take detection, computer, and communication technologies and apply them in an integrated fashion to increase the safety and efficiency of road transportation. For example, ITS is employed in Minneapolis and St. Paul, Minnesota, using a network of real-time freeway traffic detectors as part of a ramp metering system. The traffic flow information from the detectors is used as input to automated freeway capacity algorithms that regulate entry of additional vehicles onto the freeway system through modified traffic lights located at the entry ramps. Almost all state and local transportation authorities are using ITS to some extent today. ITS can be vehicle-based systems (e.g., adaptive cruise control, rear object detection) or infrastructure-based systems (e.g., vehicle surveillance, dynamic message signs). Typically it is the interaction between vehicles, the roadside, management centers, and travelers along with the synergy of data and information flows working in harmony that yield spectacular results. Linking vehicles and infrastructure electronically is expected to advance rapidly in the coming years, as it is viewed as a very cost-effective

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services means of improving safety and mobility. The application of sophisticated technologies in an integrated fashion across a number of transportation system components (i.e., vehicles, roadside, centers, and travelers) clearly requires a master plan. The transportation infrastructure (i.e., roadside and centers) in our highly decentralized transportation system must interact with vehicles of many types from many suppliers and travelers of all sorts needing to cover great distances across multiple jurisdictions. The U.S. federal government initiated extensive multistakeholder consultations in the mid-1990s leading to the development of the National ITS Architecture (National ITS Architecture Development Team, 2003). It is essentially a high-level blueprint for the application of information technologies to road transportation. First issued in 1996, the ITS Architecture continues to be refined. In 2000 the Architecture was adopted by Canada with some modifications. It is therefore well on its way to general use over most of North America, an enviable situation to promote freedom of movement and trade throughout the continent as well as collective security and global competitiveness. Indeed, the National ITS Architecture is a major body of work that will influence the evolution of road transportation for decades to come. Enhanced use of ITS can mitigate some of the negative impacts of weather on road transportation by making it possible to provide the best weather and traffic information to users in a timely and appropriate manner (Andrey et al., 2003b; Cambridge and Mitretek, 2003). For example, in response to reduced surface friction during winter weather conditions, an advanced traffic management system could modify signal timing and ramp metering to adjust vehicle spacing accordingly, alert roadway maintenance crews to treatment needs, and inform drivers in their vehicles of potentially hazardous conditions. Version 4.0 of the National ITS Architecture, introduced in 2002, included the Maintenance and Construction Management Center and the Maintenance and Construction Vehicle to more formally capture road weather and the transportation components mandated to deal with it. ITS has also been instrumental in the development of standards; for example, a group of communications standards referred to as the National Transportation Communications for ITS Protocol (NTCIP) includes standards for an ESS, NTCIP-ESS, which are open, industry-based standards that facilitate information exchange between RWIS and other ITS devices with a common communications interface. The standardization of terminology and graphical displays as well as the format and structure of messages are under development and will facilitate communication of road weather information to the public. The ESS sensors can be linked to an automatic spray

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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services system, perhaps developed by a different vendor, to dispense freeze-point depressants the instant that snow or icing conditions are detected on the road surface. Likewise, with sensors deployed according to agreed-upon standards in a coherent network over one or more jurisdictions, more sophisticated mesoscale modeling solutions could be pursued. Indeed, ITS provides a framework with which to extend road weather and other services in a fully integrated fashion across the nation, and eventually, throughout North America.