An automated highway system (AHS) or Smart Roads, is an advanced Intelligent transportation system technology designed to provide for driverless cars on specific rights-of-way.

A prototype automated highway system was tested in San Diego County, California along Interstate 5; however, despite the technical success of the program, investment has moved more toward autonomous intelligent vehicles rather than building specialized infrastructure. The AHS system places computers in cars. They read a passive roadway, and use radar and inter-car communications to make the cars organize themselves without the intervention of drivers.

The difficulty of AHS deployment is the chicken-and-egg problem, no one will buy AHS equipped cars unless there is a network that can accommodate them (and only them). And no one will build the network until there are sufficient number of AHS vehicles on the road. AHS doesn't mix with regular traffic. For this reason, most ITS research is aiming for intelligent vehicles or smart cars. Those cars can assist the driver in mixed traffic (including traditional non-smart cars), and are thus likely to be deployed sooner.

How it works

The roadway has magnetized stainless-steel spikes driven one meter apart in its center. The car senses the spikes to measure its speed and locate the center of the lane. Further the spikes can have either magnetic north or magnetic south facing up. The roadway thus has small amounts of digital data describing interchanges, recommended speeds, etc.

The cars have power steering, and automatic speed controls, but these are controlled by the computer.

The cars organize themselves into platoons of eight to twenty-five cars. The platoons drive themselves a meter apart, so that air resistance is minimized. The distance between platoons is the conventional braking distance. If anything goes wrong, the maximum number of harmed cars should be one platoon.