Delft University of Technology
Faculty Mechanical, Maritime and Materials Engineering
Transport Technology

D.D. Erwin An Overview of Automated Highway Suystems
Literature survey, Report 2004.TL.6859, Transport Engineering and Logistics.

This paper gives an overview of automated highway systems (AHS), including a discussion of the four main system architectures, the layered control system (particularly focusing on the coordination and link layers), and sensing and communication technologies used. Automation of highway vehicles and traffic oversight systems to create AHS is a candidate solution for growing congestion and safety problems. Automation can outperform human drivers by always remaining alert and reacting predictably, faster and with greater precision. This performance advantage along with the feedback control introduced by AHS would improve highway capacity and safety. Automated vehicles can maintain small following distances and eliminate human error to reach the main AHS goal of increased capacity and safety. Although AHS is supposed to prevent the need for expansion of the existing highways, researchers often call for the construction of separate highway facilities for automated vehicles.

Of the four main system architectures for AHS, the synchronous moving cell concept is the simplest, but also yields low performance. The infrastructure manages cells or slots on the highway in both time and space, which can be allocated to vehicles. A vehicle maintains its position relative to its slot rather than other vehicles as is done in the other concepts.

The autonomous system architecture involves vehicles that operate completely independent of other vehicles or the infrastructure. Any information about other vehicles is generated by a vehicle's own sensors and although the vehicle may receive information from the infrastructure it still makes its own decisions. This concept requires sophisticated technology while yielding performance no better than the synchronous moving cells concept.

The cooperative operating scheme basically adds intervehicle communication to autonomous vehicles to improve performance with respect to capacity and safety. The better-informed vehicle can maintain shorter spacing to increase capacity, while also improving safety.

By further utilizing intervehicle communication, the platooning architecture organizes vehicles into groups called platoons with small intervehicle spacing. This relatively small following distance yields high capacity and makes for low impact speed collisions, improving safety. The California PATH research group and others conclude that this concept yields the highest capacity and safety.

A layered control system is used in AHS. The bottom layer is vehicle dynamics, including sensors and actuators. The regulation layer makes use of feedback to control vehicle dynamics. The coordination layer coordinates the maneuvers required by the assigned path with neighboring vehicles, generating maneuver trajectories which are sent to the regulation layer for execution. The link layer controls traffic flow in sections or links of highway, according to the desired characteristics determined by the network layer. Each link calculates and communicates speed, spacing and path commands to vehicles in its highway section. The network layer views the entire traffic system as a network and uses optimization techniques to find desired traffic flow characteristics throughout the network.

AHS requires communication and sensing capabilities. The proximity of other vehicles can be sensed with millimetre-wave radars or laser rangefinder. Wireless, two-way communication is used both for intervehicle and vehicle-infrastructure communication. Differential GPS (DGPS) or magnetic nails buried in the road can be used to detect the location of a vehicle for navigation purposes.

Reports on Transport Engineering and Logistics (in Dutch)
Modified: 2004.10.15; , TU Delft / 3mE / TT / LT.