21-05-2012, 05:16 PM
Vehicle Platooning and Automated Highways
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T he eight-vehicle platoon demonstration at the National Automated Highway
Systems Consortium Technical Feasibility Demonstration, held in
San Diego from August 7-10, 1997, successfully demonstrated the technical
feasibility of operating standard automobiles – Buick LeSabres– under precise
automatic control at close spacings, at highway speeds. Riders experienced
real travel in a fully automated AHS vehicle, and were shown that comfortable,
high-capacity, automated travel is technically feasible in the near future.
The platoon demonstration was designed by researchers at the California PATH
program to show how vehicle automation technology can be used to make
major contribution to relieving traffic congestion. The eight Buicks operating
tight coordination showed how an automated highway system can provide
significant increase in highway throughput (vehicles per lane per hour moving
along the highway).
Since platooning enables vehicles to operate much closer together than is possible
under manual driving conditions, each lane can carry at least twice as much
traffic as it can today. This should make it possible to greatly reduce highway
congestion. Also, at close spacing aerodynamic drag is significantly reduced, which
can lead to major reductions in fuel consumption and exhaust emissions. The
high-performance vehicle control system also increases the safety of highway
travel, reduces driving stress and tedium, and provides a very smooth ride.
Lateral Control
For a vehicle to follow the road, the road has to be first marked by
some indicators that define its boundaries. The vehicle then employs
appropriate sensors to measure the corresponding physical
properties of the indicators and to determine its location with respect
to the road markings. Onboard intelligence, based on the relative
locations, commands the steering actuator to steer the vehicle and
follow the road.
The PATH automatic steering control system uses magnetic markers
buried along the road center 4 feet apart to define the roadway. By
alternating the polarities of the magnetic markers, they also transmit
such roadway characteristics as upcoming road geometry information,
milepost locations, and entrance and exit information to the vehicle.
Fault Management
A very important feature of the vehicle control system is the
automated fault management system that has been implemented on
the cars. The fault management system will both detect and handle
failures in the sensors and actuators on the vehicles. Failures are
typically detected within a fraction of a second of the time they occur.
Some failures are handled without any perceptible change being
noticed by the passengers. In some cases, however, for instance in the
case of a radio communication system failure, the spacing between
some cars in the platoon is enlarged to as much as 15 meters. In the
rare event of an actuator failure, the driver of the car will be
informed that his intervention is necessary.