The advent of low-cost, highly reliable, integrated circuits has made feasible the design and implementation of an electronic system to aid disabled motorists. A responsive electronic vehicular instrumentation system (REVIS) is presented that detects all highway incidents independent of traffic-flow rate. A cost-benefit analysis reveals that REVIS is superior to the highway patrol on limited-access rural highways.

• ONE of the greatest losses of efficiency experienced on urban highways results from disabled vehicles that either are on the shoulder of the road or block a moving traffic lane. The congestion and accompanying delay for other vehicles that result from a reduction in highway service volume are frequently more significant than the incident that causes the congestion. A 2-year study of highway incidents on the Gulf Freeway in Houston, Texas, showed that a 1-lane blockage by a minor accident or stall reduced flow by 50 percent even though only 33 percent of the road was blocked (!). An incident that blocked 2 lanes reduced flow by 79 percent. So freeway incidents create a reduction in service volume that is disproportionate to the physical reduction of the facility. The effect of a 1-lane blockage on a heavily traveled highway is shown in Figure 1. From this example, a reduction of 15 min in the time required for incident detection or police response results in significant savings of vehicle hours. In recent years there has been growing interest and research activity among state and federal highway agencies to find cost-effective methods to quickly detect, identify, and respond to highway incidents {; i i, § , t'1!!,~ 10,!!,~.! b _! t~ 1 § ...!'1.!!!,.!!!,~~~ 24). Motorist-initiated and automatic systems of detection have been developed to complement the police patrol (~ 23). The most advanced system of automatic electronic detection of highway incidents has been placed in operation on the 42-mile (67.6-km) triangle of the San Diego, Santa Monica, and Harbor Freeways in Los Angeles (~). This system detects the flow disruption produced by a highway incident by electronically monitoring the volume and occupancy in each traffic lane every 0.5 mile (0.81 km); time averages are updated every 30 s. Occupancy is defined as the percentage of time that any vehicle is over an induction-loop detector buried in the road. When gradients in occupancy and volume between adjacent highway sections are calculated in real time and are found to exceed predetermined threshold values, a light on the panel map display board located in the control center is activated. A dispatcher may then call a helicopter to make an on-site inspection of the area and transmit a television signal back to the control center. After evaluating the incident, the dispatcher calls an appropriate aid vehicle into action. A similar system is being designed for the northern corridor of the New Jersey Turnpike. An essential feature of the Los Angeles system is that some macroscopic disruption in the traffic flow must occur for an incident to be detected. On the Los Angeles triangle, which sustains 700,000 vehicles daily, this strategy for incident detection works excellently because the traffic model is valid. The primary beneficiary of this system is the driver upstream of the incident whose delay has been reduced greatly.