JPL's Wireless Communication Reference Website

Chapter: Network Concepts and Standards
Section: Road Traffic Information Systems

Automated Vehicle Control Systems

Contributed by Bret Foreman, U.C. Berkeley

Automated control of passenger vehicles is one promising method of increasing traffic density and efficiency on existing highways. Most schemes will require extensive use of wireless communication for coordination of maneuvers, stable control, safety, traffic advisories, navigation, and fault control. This requires enhancements of existing wireless technologies for control (short range communication between pairs of closely spaced vehicles), maneuver (communication among groups of vehicles), and advisory (communication between vehicles and a central, stationary database) functions. The California Partners for Advanced Transit and Highways (PATH) program investigates such systems. This program envisions closely spaced, train-like groups of one to twenty automated vehicles in special lanes separated from non-automated vehicles by barriers. Gaps between vehicles within a group would be less than two meters, bumper-to-bumper. Gaps between groups in the same lane would be over 50 meters. In this context, the control function is to maintain stability and good ride quality among the vehicles in a group; the maneuver function is for a vehicle to join or leave a group; and the advisory function is to inform the groups about conditions ahead. This application and the car-to-car propagation channel pose particular requirements to the AVCS communication system.

Figure: Autonomous vehicle control requires reliable wireless communication links. Source: California PATH

Social Motivations

New urban freeways systems cost hundreds of millions of dollars per mile. The high cost of infrastructure suggests that incremental improvements in system performance can justify the cost of vehicle modifications. Here's a simple example:
California can build a new urban freeway of 10 miles long at a typical cost of 1 billion dollars. The roadway is 4 lanes each way so about 16000 vehicles per hour may use it (2000 vehicles per hour per lane). This is peak usage so we may assume a daily usage of half this rate or 8000 vehicles per hour or a total of 192,000 vehicles per day. The question then is how many distinct vehicles does this roadway serve?

Now we note two obvious facts. First, vehicles almost always make round trips. That means that, at most, this system can serve 96,000 vehicles per day. Second, if a vehicle is not using this piece of roadway then it must be using some other piece (or sitting idle). That means that this roadway can be taken to serve the same 96,000 vehicles every day without loss of generality. A simple division shows that this roadway costs over $10,400 per vehicle! Admittedly, this huge cost is amortized over the lifetime of the roadway (perhaps 20 years) but that still adds more than $500 per year to the cost of operating each vehicle. Clearly, it makes sense to add electronics to the roadways and the vehicles to avoid building new roadways, even if those electronics add thousands of dollars to the cost of each vehicle. As a final motivation, consider the environmental and esthetic costs of new roadways versus the optimization of existing ones. All these factors taken together can justify substantial investment in a host of technologies to increase the efficiency of the existing roadway system.

Some Solutions

The PATH project at UC Berkeley is looking at a variety of applications of high technology to the problems of over crowded roadways systems. One of those applications is in so called AVCS or Automated Vehicle Control Systems. In PATH, this is envisioned to be an automated lane (or set of lanes) with all vehicles controlled by computers. The automated vehicles would follow each other in closely spaced "platoons" of two to twenty vehicles.

It is envisioned that such a system could make use of much of the existing roadway infrastructure. Automated lanes would be segregated from manual lanes by barriers but those barriers could be retrofitted onto existing roadways at reasonable cost. Entry/exit presents a more difficult but still tractable problem.

Some Technical Details

In keeping with modern design methodologies for large scale systems, each vehicle is required to operate autonomously but cooperatively. This helps such a system of vehicles to be robust and fault tolerant. A protocol has been designed that allows vehicles to coordinate their movements when joining, traveling in, and leaving a platoon. In addition, control laws have been developed to provide a stable, comfortable ride for passengers. It is assumed that vehicles will exchange information with some centralized source regarding route planning, road conditions, capacity allocation, etc. All of these activities require a capacity for wireless communication among vehicles in a platoon, among platoons, and between vehicles and some central database.

Technical Motivations

As can be seen from the discussion above, the wireless communications needs for AVCS are quite broad. We've divided them into three categories

Modulation, Directionality, and Addressing in a Mobile Environment

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JPL's Wireless Communication Reference Website Bret Foreman and 1993, 1995.