4 Roadway Conditions
4.2.3 I-40 Fog Detection and Early Warning System – North Carolina
Impetus for the Activity
Fog-related crashes, including a 46-car pileup on January 15, 1996, sparked the North Carolina DOT (NCDOT)to consider a technological treatment for this area. A conventional system of static signs with activated flashers was installed in the 1980s, but was ineffective. The system was installed with the expected result of providing early warnings of hazardous conditions and reducing crashes.
Criteria for System Selection (Hardware and Software)
The NCDOT Traffic Engineering Branch conducted a feasibility study in 1996. The study recommended three options, which were evaluated by their Board of Transportation. The current system was approved because it was the most cost effective based on available funding. The Study Team also visited the I-75 Fog Detection system in Tennessee, which is described in a separate section of this document.
Description of the System
The installation of the system was completed in September 1996 and the system is currently operational. Three closed circuit television cameras are being installed as part of the system.
The purpose of the system is to detect low visibility conditions and provide advance warning to motorists. The system also notifies the North Carolina State Highway Patrol and NCDOT maintenance personnel so they can monitor the conditions and take appropriate countermeasures.
The system covers a 13-km rural section of I-40, and consists of two overhead CMSs, three visiometers, and 13 km of fiber optic communications cable. As noted above, three closed circuit television cameras are being added to the system.
The three visiometers are used to determine when a low visibility threshold is met. When the threshold is met, messages are displayed on the two CMSs and an alert notification is sent to the North Carolina Highway Patrol and NCDOT. The messages are updated on an as needed basis as determined by the three visiometers and operators of the system. The system output is advisory in nature.
System Performance
Factors affecting system performance include the accuracy and reliability of the visiometers and operator understanding and manipulation of the system software. Proper maintenance will affect the future performance of the system.
The performance and reliability of the system were formally tested during a system test and 90-day observation period, which ended in September 1996. According to NCDOT, the system has performed satisfactorily since completion of the 90-day observation period.
System Effectiveness Evaluation
The effectiveness of the system has not been formally or informally evaluated.
Perceived “Hot Spots” for Rural ITS Deployment
It was noted that RWISs might be effective in reducing the frequency and severity of rural crashes.
Obstacles and Lessons Learned
The major obstacle for this system was the inter-agency coordination between the NCDOT and the North Carolina Highway Patrol. It is suggested that a Memorandum of Understanding be developed during the planning of a system that crosses jurisdictional boundaries.