Automated Highway Systems
A major long-term element of Intelligent Transportation Systems research and development is Automated highway Systems (AHS). The AHS program is a broad international effort “to provide the basis for, and transition to, the next major performance upgrade of the vehicle/highway system through the use of automated vehicle control technology” [NAHSC96]. The detailed definition of the Automated Highway System is as follows [Plan93]: The term “fully automated intelligent vehicle-highway system” is interpreted to mean a system that:
w Evolves from today’s roads (beginning in selected corridors); w P rovides fully automated “hands-off” operation at better levels of performance than today’s roadways in terms of safety, efficiency, and operator comfort; and, w A llows equipped vehicles to operate in both urban and rural areas on highways that are both instrumented, and not instrumented.
The consensus in the AHS community is that AHS will evolve over a series of smaller steps in technology. The final step of full automation will not be a leap, but a logical consequence of previous development and deployment efforts. Each step in the technology will have its own benefits and be self-sustaining. Vehicle and infrastructure evolutions will be “synchronous” [James94]. We will briefly mention the steps of this evolution here before introducing the AHS program and discussing automatic vehicle control technologies in detail. When the cruise control was first developed, there was much concern over the safety and user acceptance of the new system; however, it has become widely accepted and used. In the near future, obstacle and headway warning and Automatic Vehicle Identification (AVI) will be added to modern cruise control and existing communications infrastructure. The success of AHS depends on linking the power of cellular communications and the emerging range of highperformance computers to the ongoing vehicle based developments. Ideally, the highway system can be divided into a number of “cells” which contain local radio receivers or beacons that will be linked together through a fiber-optic network. Vehicles will also be equipped with a transceiver unit carrying several user services. The first applications of this technology are the Automatic Vehicle Identification (AVI) and Electronic Toll Collection (ETC). Obstacle and headway warning is the next step in AHS development in vehicles. Vehicle on-board radar (VORAD) systems in many commercial vehicles are already in use for the last two years. An important issue in warning systems is the capabilities of the sensor modules. Differentiating between a large
Chapter 2. Automated Highway Systems
vehicle and a small animal may not be possible using a simple system. A consequent application of the headway warning system is the automatic headway control. Adaptive cruise control systems are currently designed by many automobile manufacturers. The market introduction of the first vehicle with adaptive cruise control is expected in 1997. This will enable the drivers to hold their desired speed as well as the desired headway distance. Although the drivers defined as “creepers” will be cut-of by more aggressive drivers (“hunters”), the ability to set the desired headway may be desirable to many users. Also, the issues such as sensor types, curve handling, merging vehicles, changing lanes, integration of steering and braking all have to be addressed to obtain a complete system design. Applications in advanced traffic management, traveler information and public transportation systems (ATMS, ATIS, APTS) will require more sophisticated vehicle location capabilities. In addition, the number of uses for vehicle-to-roadside communications will eventually increase. MAYDAY services, fleet tracking and automatic vehicle location (AVL) applications will use radio-location beacons as well as more sophisticated transceivers. As a result of AVL...