Everyday the media brings us the horrible news on road accidents. Once a report
said that the damaged property and other costs may equal 3 % of the world's gross
domestic product. The concept of assisting driver in longitudinal vehicle control
to avoid collisions has been a major focal point of research at many automobile
companies and research organizations. The idea of driver assistance was started
with the 'cruise control devices' first appeared in 1970's in USA. When switched
on, this device takes up the task of the task of accelerating or braking to maintain
a constant speed. But it could not consider the other vehicles on the road.
An
'Adaptive Cruise Control' (ACC) system developed as the next generation assisted
the driver to keep a safe distance from the vehicle in front. This system is now
available only in some luxury cars like Mercedes S-class, Jaguar and Volvo trucks
the U.S. Department of transportation and Japan's ACAHSR have started developing
'Intelligent Vehicles' that can communicate with each other with the help of a
system called 'Co operative Adaptive Cruise Control' .this paper addresses the
concept of Adaptive Cruise Control and its improved versions.
ACC
works by detecting the distance and speed of the vehicles ahead by using either
a Lidar system or a Radar system [1, 2].The time taken by the transmission and
reception is the key of the distance measurement while the shift in frequency
of the reflected beam by Doppler Effect is measured to know the speed. According
to this, the brake and throttle controls are done to keep the vehicle the vehicle
in a safe position with respect to the other.
These
systems are characterized by a moderately low level of brake and throttle authority.
These are predominantly designed for highway applications with rather homogenous
traffic behavior. The second generation of ACC is the Stop and Go Cruise Control
(SACC) [2] whose objective is to offer the customer longitudinal support on cruise
control at lower speeds down to zero velocity [3]. The SACC can help a driver
in situations where all lanes are occupied by vehicles or where it is not possible
to set a constant speed or in a frequently stopped and congested traffic [2].
There is a clear distinction between ACC and
SACC with respect to stationary targets. The ACC philosophy is that it will be
operated in well structured roads with an orderly traffic flow with speed of vehicles
around 40km/hour [3]. While SACC system should be able to deal with stationary
targets because within its area of operation the system will encounter such objects
very frequently.
