Grouping vehicles into platoons is a method of increasing the capacity of roads. An automated highway system is a proposed technology for doing this.
Platoons decrease the distances between cars using electronic, and possibly mechanical, coupling. This capability would allow many cars to accelerate or brake simultaneously. Instead of waiting after a traffic light changes to green for drivers ahead to react, a synchronized platoon would move as one, allowing up to a fivefold increase in traffic throughput if spacing is diminished that much. This system also allows for a closer headway between vehicles by eliminating reacting distance needed for human reaction.
Platoon capability might require buying new cars, or it may be something that can be retrofitted. Drivers would probably need a special license endorsement on account of the new skills required and the added responsibility when driving in the lead.
Smart cars with artificial intelligence could automatically join and leave platoons. The automated highway system is a proposal for one such system, where cars organise themselves into platoons of eight to twenty-five.
- Greater fuel economy due to reduced air resistance.
- Reduced congestion
- Substantially shorter commutes during peak periods.
- On longer highway trips, vehicles could be mostly unattended whilst in following mode.
- Fewer traffic collisions
- Drivers would feel less in control of their own driving, being at the hands of computer software, or the lead driver
Automated highway system
An automated highway system (AHS) or Smart Road is a proposed intelligent transportation system technology designed to provide for driverless cars on specific rights-of-way. It is most often touted as a means of traffic congestion relief, as it would drastically reduce following distances and headway, thus allowing more cars to occupy a given stretch of road.
How it works
In one scheme, 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. Furthermore, the spikes can have either magnetic north or magnetic south facing up. The roadway thus provides small amounts of digital data describing interchanges, recommended speeds, etc.
The cars have power steering and automatic speed controls, which are controlled by a 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.
An overview of platooning systems is given in 
The origin of research on AHS was done by a team from The Ohio State University led by Dr. Robert E. Fenton, based on funding from the U.S. Federal Highway Administration. Their first automated vehicle was built in 1962, and is believed to be the first land vehicle to contain a computer. Steering, braking and speed were controlled through the onboard electronics, which filled the trunk, back seat and most of the front of the passenger side of the car. Research continued at OSU until federal funding was cut in the early 1980s.
The USDOT-sponsored National Automated Highway System Consortium (NAHSC) project, a prototype automated highway system, was tested in San Diego County, California in 1997 along Interstate 15. 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 sensory technology in cars that can read passive road markings, and use radar and inter-car communications to make the cars organize themselves without the intervention of drivers. Such an autonomous cruise control system is being developed by Mercedes-Benz, BMW, Volkswagen and Toyota.
The SARTRE Project (Safe Road Trains for the Environment), is a European Commission funded project investigating implementation of platooning on unmodified European motorways. The project begun in September 2009, and vehicle platooning, as envisaged by the SARTRE project, is a convoy of vehicles in which a professional driver in a lead vehicle heads a line of closely following vehicles. Each following vehicle autonomously measures the distance, speed and direction and adjusts to the vehicle in front. Once in the platoon, drivers can do other things while the platoon proceeds towards its long-haul destination. All vehicles are detached and can leave the procession at any time.
SARTRE carried out in January 2011 the first successful demonstration of its vehicle platooning technology at the Volvo Proving Ground near Gothenburg, Sweden, with a lead truck followed by single following car. In January 2012 SARTRE carried out a second demonstration in Barcelona, Spain, this time with of a multiple vehicle platoon, a lead truck followed by three cars driven entirely autonomously at speeds of up to 90 km/h (56 mph) with a gap between the vehicles of no more than 6 m (20 ft). Volvo Car Corporation was the only participating car manufacturer.
- Driverless car
- Future of the car
- Green wave
- Safe Road Trains for the Environment
- Vehicle Infrastructure Integration
- Virginia Smart Road
- Zabat, Stabile, Frascaroll, Browand, The Aerodynamic Performance of Platoons, ISSN 1055-1425
- Carl Bergenhem, Henrik Pettersson, Erik Coelingh, Cristofer Englund, Steven Shladover, Sadayuki Tsugawa, “Overview of Platooning Systems”, ITS World Congress, Vienna, 22-26th October 2012
- Engineering Newsletters - ASME. Memagazine.org. Retrieved on 2013-09-04.
- "About the SARTRE project". The SARTRE Project. undated. Archived from the original on 18 January 2011. Retrieved 18 January 2011.
- GCC staff (2010-12-11). "EU SARTRE road platooning project moving to testing phase; firsts tests of two-vehicle train by end of year". Green Car Congress. Retrieved 2013-11-25.
- GCC staff (2012-01-24). "SARTRE project completes first successful on-road demo of multiple vehicle platooning". Green Car Congress. Retrieved 2013-11-25.
- Vehicle Platooning and Automated Highways Description of the San Diego experiment.
- Underground Automated Highway Systems Forecast for the future of urban transportation.
- Safe Road Trains for the Enivironment (SARTRE)
- 1997 demo of autonomous cars platooning on I-5 San Diego, California (NAHSC)
- 2011 SARTRE Project demo, Gothenburg, Sweden (a lead truck with a single following car)
- 2012 SARTRE Project demo, Barcelona, Spain (a lead truck followed by three cars driven entirely autonomously)