Weather threatens surface transportation nationwide and impacts roadway safety, mobility, and productivity. There is a perception that transportation managers can do little about weather. However, three types of Road Weather Management strategies may be employed in response to environmental threats:

*Advisory Strategies
*Control Strategies
*Treatment Strategies.

ANTI-ICING DEICING OPERATIONS
System Operations:
Maintenance managers utilize the Internet to access weather forecast data and identify threatening winter storms or frost events. When an impending threat is predicted, maintenance vehicles are deployed to spray small amounts of the anti-icing chemical on road surfaces before snowfall begins or frost forms. Chemical application rates vary from ten to 50 gallons (37.9 to 189.3 liters) per lane mile, depending on the nature and magnitude of the threat. Maintenance crews regularly check four “indicator areas” along the highway to determine when frost on shoulder lanes begins to migrate into travel lanes. The status of these areas indicates that the road should be retreated to ensure that chemical concentrations are high enough to prevent freezing.

Transportation Outcome:
To assess the effectiveness of anti-icing operations, winter road maintenance activities were analyzed for five years prior to the anti-icing program and for three years after implementation.

AVALANCHE WARNING SYSTEM
System Components:
The avalanche warning system is comprised of a sensor assembly, a radio communication system, a controller, two Static warning signs equipped with flashing beacons, and audible alarms in maintenance vehicles. The sensor assembly includes tilt switch sensors enclosed in galvanized steel pipes. The pipes are hung on weighted wire ropes attached to a ¾-inch (19-mm) diameter cable, which is strung across the slide path. The cable is suspended roughly 8 feet (2.5 meters) above the ground and anchored to steel posts embedded in concrete. The sensor assembly is installed 980 feet (298.7 meters) above the roadway.

The controller monitors sensor status, records sensor data, and activates warning systems via radio when the onset of an avalanche is detected. The roadside warning signs are located 1,300 feet (396.2 meters) in advance of the affected highway segment. Batteries with solar panel chargers supply power to all field sensors, control devices, and communications hardware. Portable alarm devices are placed in maintenance vehicles—primarily rotary snowplows and front-end loaders—operating in the area.

System Operations:
Controller software is programmed to continuously monitor the sensor assembly and detect switch closure based upon established threshold values. When an avalanche is detected, warning devices are instantly activated. Tilt switches within the steel pipes pivot from vertical to horizontal positions when impacted by a slide causing a circuit to close. The controller automatically prompts a radio to transmit a modulated tone to activate beacons atop motorists warning signs and to sound 97-decibel sirens in maintenance vehicles. The audible alert gives maintenance personnel about ten seconds to move out of the slide path.

Transportation Outcome: The avalanche warning system improves roadway safety by minimizing risks to drivers and to maintenance personnel. The system also facilitates timely inspection of the roadway after an avalanche, snow and debris removal activities, and road
closure or rescue operations.

FLOOD WARNING SYSTEM
System Components: The flood warning system consists of stilling wells, Remote Processing Units (RPUs), Dynamic Message Signs (DMS), a radio communication system, and a central computer system. A stilling well is comprised of a 3-foot (0.9-meter) long pipe, a pressure transducer, and a float switch to measure stream levels. When high water is detected, RPUs activate sign assemblies and report stream levels to the central computer. Each RPU—which is housed in a polemounted enclosure—includes radio communication devices, solar or electrical power systems, and controls to reset sign assemblies. At each monitoring site, one to four sign assemblies are installed near the road to alert motorists. Sign assemblies include electromechanical DMS, two flashing beacons, radio communication
devices, and power systems.

System Operations:
When water reaches the roadway edge RPUs automatically activate flashing red beacons and change sign messages from “HIGH WATER WHEN FLASHING” to “DO NOT ENTER HIGH WATER”. Sign assemblies send a message back to the RPU to verify proper operation. Remote processing units transmit water level and sign status to the central computer every hour via the radio communication system. When high water is detected by field components, the central computer is immediately alerted and sends alphanumeric pages to maintenance staff who then erect barricades on threatened roads. The central computer also posts road closures on the City’s “Flooded Roadway Warning System” web site (www.ci.dallas.tx.us/sts/html/frws.html). When the water recedes, maintenance staff are paged again to notify them that barricades can be removed and signs assemblies can be reset.

Transportation Outcome:
The flood warning system improves roadway safety, as most motorists heed sign warnings and avoid hazardous conditions. Further, since the system was installed in April 2000 no claims related to flooded roads have been filed against the City.

HIGH WIND WARNING SYSTEM
System Components:
Traffic managers utilize an Environmental Sensor Station (ESS) to monitor wind direction and wind speed. The ESS is part of a statewide Road Weather Information System (RWIS), which collects and transmits environmental data to district offices via a Wide Area Network. Four Dynamic Message Signs (DMS) are installed on the roadway to display messages to eastbound and westbound motorists.

System Operations:
Traffic managers employ an advisory strategy to alert motorists of high wind conditions and a control strategy to restrict high-profile vehicle access during severe crosswinds. Traffic and maintenance managers are alerted by the RWIS when wind speeds in the area exceed 20 mph (32 kph). A warning message—“CAUTION: WATCH FOR SEVERE CROSSWINDS”—is displayed on DMS when wind speeds are between 20 and 39 mph. When severe crosswinds (i.e., over 39 mph (63 kph)) are detected, a restriction message is posted on DMS to direct specified vehicles to exit the freeway and take an alternate route through Livingston. A typical restriction message reads “SEVERE CROSSWINDS: HIGH PROFILE UNITS EXIT”. DMS may also be used to warn drivers of poor pavement conditions (i.e., snow or ice) during winter months.

Transportation Outcome:
Before DMS were installed, maintenance personnel had to erect barricades on the freeway to prevent high-profile vehicles from entering the affected highway section and being blown over or blown off of the road. Advising drivers and restricting access under high wind conditions has improved roadway safety, as well as the productivity and safety of maintenance staff.

ROAD WEATHER INFORMATION FOR TRAVELERS
System Components:
The private company—Meridian Environmental Technology—operates a system that ingests data from various sources including the DOT’s roadside Environmental Sensor Stations, the Agricultural Weather Network managed by the University of Nebraska, National Weather Service (NWS) Doppler Radar, NWS satellite data, Federal Aviation Administration surface weather observations, as well as field reports from DOT and State Patrol personnel. The data are transmitted, via various communications systems, to computers at Meridian’s North Dakota office that perform advanced weather forecast processing. These computers generate data for 6.2-mile (ten-kilometer) grids across the state and disseminate tailored road weather information via an interactive telephone system and the Internet. The DOT has installed road signs, depicted in the figure, along state highways to advise motorists of the 511 service.

System Operations:
When travelers dial 511, from cellular or landline telephones, the system asks for the caller’s route of interest (i.e., highway and direction). The information system integrates weather analysis and forecast data with road attribute data to provide the caller with a customized, route-specific pavement condition report and six-hour weather forecast extending roughly 60 miles (or one hour) in their direction of travel.

Traveler information provided via 511 is also available on the Internet (www.safetravelusa.com, soon to be www.511bystate.com). Users can view a state map and detailed regional maps with color-coded highways. When a colored freeway segment is selected, a textual road condition and weather report is displayed. This information can also be accessed via links on the State Patrol and DOT web sites (www.nebraskatransportation.org). Travelers can also access road weather data for neighboring states including Minnesota,
Montana, North Dakota, and South Dakota.