Where the Weather Meets the Road A Research Agenda for Improving Road Weather Services (2004) / Chapter Skim
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3 Current Meteorological and Transportation Activities Relevant to Road Weather
3 Current Meteorological and Transportation Activities Relevant to Road Weather
Pages 33-75
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From page 33... ...
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)
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. These data are important in the verification of weather fore casts, in providing real-time weather information to the aviation commu nity, and as input into data assimilation systems for numerical weather prediction.
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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)
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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.
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, 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.
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Despite this institutional limitation, the NEXRAD is able to track precipita tion, 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)
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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.
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SOURCE: NOAA's Forecast Systems Laboratory. cautions on dynamic message signs.
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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 3973 miles per hour)
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From page 42... ...
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 in sights 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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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.
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, improved numerical methods including the ability to specify the initial conditions for the model using data assimilation, increased avail ability of observations, and increased power of supercomputers. When the accuracy of human-produced forecasts is assessed, it is noted that it tracks closely with the skill of the objective numerical weather prediction models, reflecting the strong dependence of human forecasters on the increased skill of numerical models (Figure 3-10)
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Regional mesoscale numerical weather prediction models, with grid spacings down to a few kilometers and that are typically nested within a larger operational model, are currently being run by university researchers, private sector forecasting businesses, and local NWS partnerships. These efforts are proving themselves to be useful for highway maintenance decision making.
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This software allows forecasters to ma nipulate and edit grids, which can be initialized directly from a variety of operational numerical weather prediction models. A variety of graphical, tabular, and text products can then be derived from the gridded informa tion.
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From page 47... ...
This approach to determining a forecast, known as ensemble forecasting, provides useful information about the possible future evolution of the atmosphere in a probabilistic sense. Ensemble forecasting contrasts with the traditional method of taking the best available model and running it until it loses skill due to the growth of errors introduced in the initialization.
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From page 48... ...
public statement "Enhancing Weather Information with Probability Forecasts" (http://www.ametsoc.org/ AMS/policy/enhancingwxprob_final.html) was adopted by the AMS Coun cil on January 13, 2002, and argues strongly for increased delivery of weather forecast information in probabilistic terms.
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From page 49... ...
Another project being supported by the FHWA with additional state departments of transportation, private, and international collaboration is FORETELL (http://www.foretell.com) , an advanced weather prediction system that is being developed with the goals of reducing winter-related accidents and creating a viable road and weather information network.
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More information about these products can be found at http:// www.meridian-enviro.com/products/trans.html. Communicating Weather Information to Drivers A variety of methods are available for communicating weather informa tion to drivers.
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w=1280&h=994 Washington -- http://www.wsdot.wa.gov/Rweather/ FIGURE 3-12 Example of a map from the Iowa Winter Road Conditions Web site (http: //www.iowaroadconditions.org)
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Dynamic message signs are another important way to communicate to drivers (Figure 3-14)
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In some places, the signs advise motorists to dial 511 or tune into Highway Advisory Radio, a traffic information dissemination tool widely used by traffic managers, construction crews, and roadway maintenance personnel. Only limited use has been made of dynamic message signs to alert drivers of poor weather conditions, even though the signs are an attractive communication mechanism because drivers do not need to take any special information retrieval action.
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Dispatchers are extremely busy and do not want to be dis tracted by information that does not directly require their attention. An objective for improving communication in the trucking industry is the complete integration of roadway and weather information into a dispatcher's routing and dispatching software.
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From page 55... ...
Surface sensors, such as the one shown in Figure 3-16, can provide information on water coverage, snow, black ice, temperature, and even the amount of chemical present in a slurry on the pavement surface. There are over 2,000 ESS owned by state transportation agencies; over 1,400 are field components of Road Weather Information Systems (RWIS)
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56 WHERE THE WEATHER MEETS THE ROAD FIGURE 3-15 Environmental Sensor Station. SOURCE: Curt Pape, Minnesota Depart ment of Transportation.
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of traffic and road conditions has become popular recently. With sophisticated image processing algorithms, informa FIGURE 3-17 Visual detector.
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Energy balance models include weather information, heat and moisture exchange between the surface and the atmosphere, and the effects of precipitation,
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Energy balance models have been used to predict road surface temperature since the 1980s when the U.K. Meteorological Office first used an energy balance model to predict the surface temperature of a dry road (Rayer, 1987)
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developed a set of empirical relationships between changes in weather conditions and road surface temperature. Takle (1990)
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(c) Road surface temperature and wind speed along the roadway as presented to the user community.
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This decision depends on road surface conditions (e.g., temperature, chemical levels, and precipitation) during a 2- to 4-hour window, the typical time for a mainte nance route.
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With the introduction of new methods and technologies, winter maintenance managers and supervisors needed a better understanding of weather forecasting, snow and ice control chemicals, effective brine-making techniques, optimal application rates, dilution caused by weather and traffic, and pavement temperatures. Individual state agencies developed ad hoc training, but reductions in roadway maintenance staffs and the increased use of contractors resulted in a less experienced and smaller workforce.
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Traffic managers monitor roadway conditions and traffic incidents from traffic management centers. They use weather observations and forecasts from the commercial sector, including the media, to execute control strate gies to manage traffic flow and advisory strategies to disseminate road weather information (Pisano et al., 2002)
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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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. 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.
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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.
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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.
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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.
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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)
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Overall, the costversus-benefits remains unknown. Several research efforts will be necessary for effective emergency management of the roadway environment.
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. The effect of weather on roadway construction goes beyond physical damage; it has an economic impact as well.
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. 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.
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. 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.
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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.
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