This conference paper evaluated a vehicle guidance system designed to give safe driver-assistance to freeway traffic in heavy fog. A benefit-cost analysis was conducted to estimate the performance of the system prior to deployment. The proposed system was designed to use administrative pace-vehicles equipped with millimeter radio wave sensors and GPS technology to lead freeway traffic through heavily fogged areas subject to road closures.

The Japan Highway Public Corporation (JH) tested the sensor technology and found it had little ability to detect small or rounded objects such as tires or rubber cones. The sensors were; however, able to detect vehicles (or a corrugated board case 0.375 x 0.475 x 0.375 m) through 100 meters (m) of heavy fog.

The proposed system would attach sensors to leading-vehicles and allow groups of freeway traffic to follow using a warning vehicle in the rear. The emergency management center would monitor each ITS-vehicle using GPS and enable them to track each others position.

BENEFIT/COST ANALYSIS

Cost calculations were measured based on the following:

• Time lost and running-costs for detoured travelers on each expressway.
• Time lost and running-costs for ordinal travelers on arterial routes subjected overflow.
• Decreases in JH toll revenues.
• System start-up costs (vehicles and equipment).
• Operations and maintenance costs.
• Personnel costs (estimated for 3 months during fog season).

The estimated number of guidance-vehicles and frequency of deployment was estimated from similar snow removal operations conducted in the Sekigahara Region of the Meishin Expressway. Based on this experience, guidance vehicles were scheduled to provide service every 15 minutes on the Kanetsu Expressway, and every 20 minutes on the Oita Expressway.

Benefits were measured by estimating a 75 percent reduction in costs generated by road closures, based on the occurrence of fog-caused road closures on the Oita Expressway.

RESULTS

The results showed that traffic control using guidance-vehicles was cost effective.

• The overall benefit-to-cost ratios ranged from 1.7 to 2.1 for the Kanetsu Expressway.
• The overall benefit-to-cost ratios ranged from 1.8 to 2.2 for the Oita Expressway.

The millimeter radio wave sensor performed well under foggy conditions, however, its performance was greatly influenced by the size and shape of objects, and the waves reflected from adjacent obstacles.