4 Roadway Conditions
4.2 Poor Visibility
4.2.1 Idaho Storm Warning System
Impetus for the Activity
The problem that sparked Idaho Transportation Department (ITD) to consider a technological treatment was occasional severe weather conditions, with blowing snow or dust, on I-84, milepost 224 to milepost 269. This area experienced 18 major crashes during 1988-1991 involving 91 vehicles, 9 fatalities, and numerous serious injuries. These crashes related to an estimated $3 million in economic loss.
Initially, ITD installed two overhead message signs. Truckers reporting at the port of entry alerted the personnel of severe weather conditions. These personnel then manually activated the signs. The problem with this scenario is that the reporting was after the fact, but some reduction in the crash rate was observed.
The purpose of the Idaho Storm Warning System was to investigate various sensor systems that could provide accurate and reliable visibility and weather data, which would, in turn, be used to provide general warnings, speed advisories, and possible road closure information to travelers via existing and new VMSs. The primary goal of such a system is a major reduction in multivehicle crashes related to reduced visibility.
Criteria for System Selection (Hardware and Software)
Three systems were selected for data comparison. The systems were different in the way that information was collected and the type of information that was collected. The three systems include:
- SCAN System: Two separate visibility sensors, wind speed and direction, air temperature, relative humidity, type and amount of precipitation, and pavement conditions.
- HANDAR System: Visibility sensor, and weather measurement sensors similar to the SCAN systems.
- LIDAR System: Laser/radar-based visibility sensor that covers a larger area. This system dropped out of the test due to extensive technical and reliability problems.
Description of the System
The system was installed in 1993 and is still operational. The project was completed in the summer of 2000. At the end of the project, the equipment will be used by ITD to continue monitoring weather and road conditions in the area.
The objective of the system is to provide early warning of storms and corresponding poor driving/road conditions. The system is to provide accurate information to motorists, warning them of dangerous conditions using VMSs.
The overall goal of the operational tests is to improve safety and reduce visibility related multivehicle crashes in the defined area.
Other goals of the operational test include:
- Evaluating the performance of the individual functional areas of each system;
- Assessing the requirements of the database;
- Estimating system costs to obtain required coverage;
- Assessing the performance of the system and its potential impacts;
- Evaluating the performance of the individual functional areas of the systems, including the:
- selected sensor system suite,
- VMS component,
- database component,
- control strategies component,
- traffic information distribution component, and
- human interface.
- Evaluating the costs relative to benefits;
- for operational test, and
- for deployment.
- Evaluating operator acceptance as reflected in attitudes and frequency of use.
The weather and road condition monitoring and warning systems were installed on a rural stretch of interstate in southeastern Idaho. The project includes nearly 160 km of rural interstate in Idaho and Utah. The primary focus is a 32-km section in the northwestern portion of the project area. The system includes four VMSs, automatic traffic counters to measure traffic speed, a VMS control center, a master data collection and test control center, and multiple weather-related detectors.
The system uses weather conditions, road conditions, and video as inputs, which are obtained using the various sensing devices and a video camera. Weather is sampled every 5 min from each sensor. If visibility readings from any of the three sensors fall below 364 m, maintenance crews are notified. Output is advisory and is made available to motorists on the VMSs, which are turned on by ITD personnel.
System Performance
The system has performed satisfactorily, and the performance and reliability of the system are being formally tested. Measures of effectiveness for system performance include visibility readings, video of targets, and system reliability.
System Effectiveness Evaluation
A formal evaluation of system effectiveness is in process. The evaluation is being performed by an independent team from the University of Idaho and Boise State University. The main measure of effectiveness is driver behavior (speed) versus weather/road conditions.
Obstacles and Lessons Learned
ITD noted a number of lessons learned, including:
- Do not underestimate the importance of system integration;
- Utilities (power and phone), even though they existed, were unreliable and in some cases damaging to equipment; and
- Mother Nature never cooperates.