|
Weather Applications > Weather Detection |
|
What are Weather Detection Systems? Weather Detection Systems use different types of sensors to detect current weather conditions such as:
These sensors are often integrated with other weather-related ITS technologies to forecast weather conditions. Road weather information systems, for example, transmit pavement temperatures and other information to traffic management centers which can, in turn, make decisions on whether to apply anti-icing chemicals or begin snowplow operations, as well as alert travelers to adverse driving conditions. Many weather detection systems can generate weather forecasts and disseminate traveler information. Other weather detection systems can also direct the maintenance of roads affected by weather. Most anti-ice technologies are integrated with road weather information systems. Combined, they create a system that can maintain roads in adverse weather conditions while providing weather forecasts and informing travelers of road conditions. Still other weather detection systems can provide forecasts, disseminate traveler information, and control traffic in adverse road-weather conditions. The Tennessee Fog Detection and Warning System integrates fog sensors, speed detectors, highway advisory radio, variable message signs, and static signs. This system can predict heavy fog and then instruct drivers to drive at a designated safe speed. See also our Telecommunications Diagrams on Weather detection systems can decrease the number of accidents and increase road safety by preparing drivers and highway agencies for poor weather. Road maintenance crews can respond with greater efficiency to weather conditions when they receive reliable information from weather sensors. Similarly, traffic management centers can use information from weather sensors to control traffic speeds and routes, thereby enforcing safe driver behavior. Weather Detection Sensors and How They Work Road weather information systems, which use an environmental sensor system to collect weather and road surface data, are the most useful type of technologies for measuring ice and snow levels. These systems consist of pavement sensors along roadways that relay information about pavement and air temperature, precipitation accumulation, and wind speed to remote processing units. These units collect and relay environmental data to a central processing unit that is usually located in a highway maintenance facility. Central processing units communicate, collect, archive, and distribute the data. The raw data are used directly or in coordination with a service provider to prepare nowcasts (which describe current weather conditions) or forecasts. Most ice sensors measure liquid water content or use forward scattering spectrometer probes. Liquid water content is measured by a microprocessor that runs an algorithm that in turn inputs icing rate, velocity, and temperature. With that information it can estimate liquid water content. This type of measurement can be accurate to within 30%. Forward scattering spectrometer probes measure the diameter of water droplets by the forward scattering of laser light through water drops. Nephelometers measure the light scattered in a forward direction by fog particles and are the most widely used and cost-effective fog sensors. They provide accurate fog density measurement in a selectable output format (visibility in distance units or voltage proportional to fog density). These sensors have low maintenance requirements and are designed with roadside highway use in mind; they are small and lightweight and their light emitters and detectors are contained within their housing, eliminating the need for external lenses and windows. A nephelometer sensor unit consists of an optical system, electronics, and software for communication to a host computer. The data obtained by the detector are digitized and transferred to the host computer. Once the host computer requests fog density data from each sensor, it determines the level of warning based on a pre-established conversion equation. Storm sensor systems use forward scatter detection technology to measure visibility and determine the type of storm (i.e. hurricane, snow, ice and the like). Other storm detection instruments measure wind speed and direction, precipitation amount, air temperature, relative humidity, roadway surface conditions, and the type and rate of precipitation. Weather detection systems can also transmit information about road-weather conditions to traffic management centers, which can, in turn, disseminate that information to drivers via highway advisory radio, variable messages signs, or cell and satellite phone services, and the Internet.
Costs vary widely according to the scope and complexity of the system. Implementation and Operational Challenges In 2004, the Transportation Research Board and the Board on Atmospheric Sciences and Climate published "Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services." http://www.nap.edu/openbook/0309091365/html/ The authors suggest that poor coordination of existing resources and knowledge has resulted in lack of implementation of enhanced weather information to a variety of users. The authors recommend establishing a coordinated national road weather research program to maximize use of available road weather information and technologies. They also suggest standardizing formats of geolocated data and improving education and training of road weather information users. Maintenance Decision Support System (MDSS) Project After several years of testing, in 2004 the Federal Highway Administration released the Maintenance Decision Support System, a software tool aimed at helping winter maintenance managers make decisions based on better weather forecasting information. The software system provides specific forecasts of road surface conditions and treatment recommendations customized for snowplow routes. A team of five national labs participated in the development and implementation of the tool, which was tested during the winters of 2002-2003 and 2003-2004 in Iowa. According to the FHWA, the road treatment guidance provided to MDSS users addresses fundamental winter maintenance questions such as "what," "how much" and "when." The system then recommends a treatment plan that includes whether to plow, whether to use chemicals and how much, and when to apply treatments. A third demonstration is scheduled to take place in Colorado in 2005. FHWA and its testing partners expect the private sector will simplify the integration of MDSS capabilities into their winter maintenance technology product lines. For more information see:
For the Federal Highway Administration’s MDSS update, go to: Road Weather Information Systems A road weather information system utilizes historic and current climatological data to develop real-time road and weather forecasts for roadway users. These systems use specialized equipment and computer programs to monitor air and pavement temperatures in order to predict whether precipitation will freeze on the pavement. Sensors collect real-time data on air and pavement temperatures, precipitation, and the amount of deicing chemicals on the pavement. Combined with information from meteorological services, they predict pavement temperatures for a specific area, such as a mountain pass, over a 24-hour period. These predictions are then transmitted to a computer at the highway agency's winter maintenance center where they form the basis for an effective anti-icing strategy. Deicing chemicals must be applied about an hour before pavement reaches freezing temperatures in order to prevent ice from forming. Using portable computers linked by modem to the central computer, maintenance managers can monitor conditions and advise motorists and dispatch crews as necessary. Tennessee Fog Detection and Warning System A chain-reaction collision involving 99 vehicles in December 1990 prompted installation of a fog detection and warning system on Interstate 75 in southeastern Tennessee. The system covers 19 miles including a three-mile, fog-prone section above the Hiwassee River and eight-mile sections on each side. Traffic center managers with the Tennessee DOT and Tennessee Highway Patrol access a central computer system that collects data from eight fog detectors, and 44 vehicle speed detectors. By continually monitoring fog and speed sensor data, the computer system predicts and detects conditions conducive to fog formation, and alerts managers when established threshold criteria are met. Highway Patrol personnel visually verify onsite conditions. Source: Tennessee Fog Detection and Warning System http://www.benefitcost.its.dot.gov/ITS/benecost.nsf/ID/583F256CEA4239E685256AFD006764DF California’s Automated Fog Warning System Tule fog, as it is called by residents of California’s Central Valley, was responsible for more than 200 crashes, 130 injuries and 18 fatalities on a stretch of I-5 between 1973 and 1994. The dense fog typically occurs during winter months. In 1995 the California Department of Transportation (Caltrans) installed an automated fog warning system that uses nine roadside weather and visibility monitoring stations and 36 detectors lodged in the pavement. A computer system provides decision support by correlating field sensor data with pre-determined response scenarios. Motorists are advised of prevailing conditions via flashing beacons atop static signs, information broadcast over advisory radio frequencies, and messages posted on dynamic message signs. Under the worst conditions, when fog is especially dense, access to affected areas of the highway is restricted. Caltrans reports that the number of fog-related accidents has been cut by nearly 70 percent on two stretches of I-5 and Highway 120 where the system has been installed. In 2005 the agency plans to expand the system to sections of Highway 99. Sources: http://www.its.berkeley.edu/publications/UCB/99/PRR/UCB-ITS-PRR-99-28.pdf http://www.dot.ca.gov/dist07/aboutdist7/pubs/journals/jan_mar_2003/html/janmar03.htm Fog Mitigation System in South Carolina A fog mitigation system monitors visibility conditions on I-526 near the Cooper River in Charleston, South Carolina. When weather conditions warrant, motorists are warned of adverse driving conditions. Source: "South Carolina DOT Low Visibility Warning System" http://ops.fhwa.dot.gov/weather/best_practices/CaseStudies/021.pdf Automated Local Evaluation in Real Time (ALERT) ALERT uses remote sensors in the field to transmit environmental data about flooding to a central computer in real time. There are various types and manufacturers of ALERT hardware and software, but they are all designed to meet a common set of communications criteria, making most equipment and programs interchangeable. ALERT systems have become a standard in real-time environmental data collection because of their accuracy, reliability, and low cost. The benefits of using ALERT are a low cost/high benefits ratio, real-time data acquisition and most of all, automated warnings. Source: http://www.alertsystems.org/ This is an excellent source of completed and on-going projects that focus on the testing and deployment of advanced technologies for road weather monitoring and forecasting. Members of Aurora include departments of transportation from a number of states as well as Canadian provinces. The organization works closely with the Federal Highway Administration, university research institutions, and various international groups. Improvement of existing road weather information services is a high priority for the organization. The program Web site is here: http://www.aurora-program.org For a list of its projects, go to http://www.aurora-program.org/documents/2004-2005WorkPlan_000.pdf "Winter Road Maintenance Decision Support System Project: Overview and Status," Paul Pisano, Andrew Stern, William Mahoney III, William Myers, and Dennis Burkheimer. Sixth International Symposium on Snow Removal and and Ice Control Technology of the Transportation Research Board Committee on Winter Maintenance, June 7-9, 2004. "A New Support System for Winter Maintenance," Focus, Federal Highway Administration, September 2004 "Where the Weather Meets the Road," Report in Brief, The National Academies, 2004 Mahoney, William. "An Advanced Winter Road Maintenance Decision Support System." Eleventh Annual ITS America 2001 Meeting. "Surface Transportation Weather Decision Report Requirements, Preliminary Interface Requirements/Draft version 2.0," Mitretek Systems, Inc., October 2000. Last Updated: April 6, 2005 |
|