Autonomous cruise control is an optional cruise control system appearing on some more upscale vehicles. The system goes under many different trade names according to the manufacturer. These systems use either a radar or laser setup allowing the vehicle to slow when approaching another vehicle and accelerate again to the preset speed when traffic allows. ACC technology is widely regarded as a key component of any future generations of intelligent cars.
TYPES OF CRUISE :
Laser-based systems are significantly lower in cost than radar-based systems; however, laser-based ACC systems do not detect and track vehicles well in adverse weather conditions nor do they track extremely dirty (non-reflective) vehicles very well. Laser-based sensors must be exposed, the sensor (a fairly-large black box) is typically found in the lower grille offset to one side of the vehicle.
Audi A4 (see a demonstration on YouTube), A5, Q5, A6, A8 (with GPS and front camera input), Q7
BMW 7 Series, 5 series, 6 series, 3 series (Active Cruise Control)
2004 Cadillac XLR, 2005 STS, 2006 DTS
2007 Chrysler 300C
2006 Ford Mondeo, S-Max, Galaxy, 2010 Taurus 
2003 Honda Inspire, Legend
Hyundai Genesis (Smart Cruise Control, delayed)
Infiniti M, Q45, QX56, G35, FX35/45/50 and G37
1999 Jaguar XK-R, S-Type, XJ, XF
2000 Lexus LS430/460 (laser and radar), RX (laser and radar), GS, IS, ES 350, and LX 570
Lincoln MKS, MKT
1998 Nissan Cima, Nissan Primera T-Spec Models (Intelligent Cruise Control)
1998 Mercedes-Benz S-Class, E-Class, CLS-Class, SL-Class, CL-Class, M-Class, GL-Class, CLK-Class
2010 Porsche Panamera, 2011 Porsche Cayenne
Range Rover Sport
Renault Vel Satis
Subaru Legacy & Outback Japan-spec called SI-Cruise
1997 Toyota Celsior, Sienna (XLE Limited Edition), Avalon, Sequoia (Platinum Edition), Avensis, 2009 Corolla (Japan) , 2010 Prius
Volkswagen Passat, 2003 Phaeton, Touareg, 2009 Golf
Volvo S80, V70, XC70, XC60, S60
In August 1997, Toyota began to offer a "radar cruise control" system on the Celsior. Toyota further refined their system by adding "brake control" in 2000 and "low-speed tracking mode" in 2004. The low-speed speed tracking mode was a second mode that would warn the driver if the car ahead stopped and provide braking; it could stop the car but then deactivated. In 2006, Toyota introduced its "all-speed tracking function" for the Lexus LS 460. This system maintains continuous control from speeds of 0 km/h to 100 km/h and is designed to work under repeated starting and stopping situations such as highway traffic congestion. The Lexus division was the first to bring adaptive cruise control to the US market in 2000 with the LS 430's Dynamic Laser Cruise Control system.
Radar-based sensors can be hidden behind plastic fascias; however, the fascias may look different from a vehicle without the feature. For example, Mercedes packages the radar behind the upper grille in the center; however, the Mercedes grille on such applications contains a solid plastic panel in front of the radar with painted slats to simulate the slats on the rest of the grille.
In car steering it consist of four buttons.......................
"ON" Button- it is used to ON the cruise control of the car
"OFF" Button-it is used to OFF the cruise control of the car
"UP arrow"button-it is used to increase the speed of the vehicle when it is engaged
"DOWN arrow" button-it is used to decrease the speed of the vehicle when it engaged
DETAILED FLOW DIAGRAM: