Longitudinal Collision Avoidance  

INTRODUCTION

Longitudinal collision avoidance technologies address rear-end and backing collisions, which can happen when a vehicle is following too closely for the driver to react to sudden braking by the lead vehicle, or when a vehicle backs into an object or vehicle. Rear-end collisions are very common, representing about 30% of all collisions between vehicles and 5.2% of fatal collisions nationwide. The National Highway Traffic Safety Administration (NHTSA) estimates that about 88% of rear-end collisions in the United States are caused by driver inattention or by vehicles following too closely.

Backing collisions, which usually occur at lower speeds, typically involving parking maneuvers. They consist of about 2.1% of all crashes, the majority of which are property damage only.

Rationale

The fact that such a large percentage of longitudinal collisions are due to driver inattention or misjudgment, and the relatively simple technology needed for forward- and backward-looking detection suggest a large potential gain from successful implementation.

Additionally, reliable rear-end collision avoidance technologies are the first step towards achieving a reliable and safe system for "smart" highways, or electronic "tow-bars," which would allow closer following and increased capacity of existing roadways.

These technologies are also being developed in connection with transit applications, which would permit precision docking and greater automation of buses, enabling closer to rail-quality service without rail's accompanying high infrastructure investments.

Finally, backing systems, such as a parking-assist technology introduced by Toyota at the end of 2003, could reduce congestion by speeding up the parking process and possibly increase parking capacity by allowing closer spacing of vehicles.

SYSTEM DESCRIPTION

Principles of Operation

A collision avoidance system generally operates in the following manner: a sensor installed at the front or back end of a vehicle constantly scans the road for vehicles or obstacles. When one is found, the system determines whether the vehicle is in imminent danger of crashing, and if so, a warning is issued, or a collision avoidance maneuver is undertaken, depending on the system.

Systems are predominantly autonomous, where detection is independent of whether other vehicles on the road are equipped with collision avoidance devices; but can be cooperative, where detection relies on vehicle-to-vehicle or vehicle-to-infrastructure communications to exchange information on the vehicle’s presence, location, lane of travel, and speed, among other factors.

The typical criteria for activation of collision avoidance are:

  • Time-to-collision: the system determines whether a collision is likely to happen at prevailing speeds and distances within a certain time interval. In a car-following situation, the time-to-collision is the time taken for the two vehicles to collide if they maintain their present speed and heading and
  • Worst-case scenario: the system assumes that the lead vehicle could brake at full braking power at any time. In essence, it maintains a "critical clearance," the minimum distance necessary to come to a stop in the event the leading car suddenly brakes.

Warning devices include:

  • Visual heads-up displays on the windshield in the driver's field of view, so that their content can be assimilated in conjunction with the driving scene ahead. These displays are intended to minimize distraction from driving tasks, in addition to ensuring that the warning does not go undetected.
  • Audio signals: in comparison to visual signals, auditory signals appear to be less intrusive. They also can operate even if lighting is poor or the windshield is obscured.
  • Haptic devices, which use tactile cues, such as vibrations or stiffening of the speed controls.
  • LED displays: these have been pilot tested in 2003 on a system devised for bus drivers.

Early research was done on a variety of sensor technologies, including passive infrared, laser radar, and video detection. One of the more promising avenues seems to be combining various technologies into what is called "sensor fusion."

Systems In Development

California Partners for Advanced Transit and Highways (PATH), Automated Bus Rapid Transit Technologies Demonstration

Demonstration in August 2003 of some key technologies for precision docking, automated lane-keeping and other operations. Sensing, actuation, communication and computation systems permit fully automated operation.

GM/Delphi Delco: Sensor fusion

In March 2003, GM and Delphi Delco launched a 10-month field test, carried out by the University of Michigan Transportation Research Institute, in which a group of Michigan drivers tested 10 Buick LeSabres equipped with collision warning systems. The testing used sensor fusion. This entailed the use of a GPS digital map to locate the vehicle and its direction of travel on a map, a forward-looking machine-vision system using lane markings to estimate the road geometry ahead of the vehicle, and radar tracking that uses the trajectories of tracked vehicles ahead to determine if there is a pattern that may indicate the upcoming road geometry. The system also included a heads-up display, which issued visual and audible warnings the closer the car came to a potential impact.

Adaptive cruise control uses the same sensors as the forward collision warning system, including the radar sensor mounted at the front of the car to detect objects in its path. If the lane ahead is clear, the system maintains the set speed, akin to conventional cruise control. When a vehicle is detected directly ahead of the car, the system adjusts vehicle speed to maintain a driver-selected clearance from the vehicle ahead.

This technology is now offered in select models.

Honda: Collision mitigation brake system

Honda Motor Company has developed a Collision Mitigation Brake System that predicts rear-end collisions and assists brake operation to reduce the impact. The system determines the likelihood of a collision based on driving conditions, distance to the vehicle ahead, and relative speeds, and uses visual and audio warnings to prompt the driver to take preventive action. It can also initiate control assistance, braking to reduce the vehicle's speed. Honda will offer the system in one model on the Japanese market in June 2005.

Toyota: "Self-parking" cars

In late 2003, Toyota announced a Toyota Prius that has the ability to "park itself," using an assistive system. Electronically operated power steering and sensors help guide the car when reversing into parking spaces.

DaimlerChrysler, IVECO, Renault Trucks and others: CHAUFFEUR Electronic "tow-bars"

The original CHAUFFEUR 1 project successfully demonstrated the electronic coupling of two trucks, using an electronic "tow-bar." CHAUFFEUR 2 demonstrated the CHAUFFEUR Assistant, a system that transfers to all vehicles by interoperable system functions. The system is a combination of smart Adaptive Cruise Control (for shorter distances) and vision-based lane keeping. CHAUFFEUR also demonstrated platooning, another extension of the tow-bar technology that allowed it to tow more than one vehicle. Three-truck platoons were demonstrated. Implementation of platooning, however, is expected to take more time – as this type of trucking operation may only be practical on dedicated truckways, which are not widespread.

 

References

"Advance Collision Avoidance Field Test Launched in Michigan," IVSource.net, March 29, 2003.

Balvanyos, Tunde, et al. "SmartBRT: A Set of Planning, Analysis and Evaluation Tools for Bus Rapid Transit: Final Report Year 1 of 2." California Partners for Advanced Transit and Highways research report. http://www.its.berkeley.edu/publications/UCB/2003/PRR/UCB-ITS-PRR-2003-07.pdf

Bonnet, C. et al. "Fuel Consumption Reduction Experienced by Two PROMOTE-CHAUFFEUR Trucks in Electronic Towbar Operation." Report from ITS Benefits and Costs Database (US DOT). http://www.benefitcost.its.dot.gov/its/benecost.nsf/0/80B3FD71200FCBBD85256AE70044B0F2

"Chauffeur Shows Off: Demos of Electronic Tow-Bar Functions Dazzle Crowd in Italy." IVSource.net. June 14, 2003.

Frye, Cathy. "International Cooperation to Prevent Collisions at Intersections," Public Roads Magazine, July/August 2001. Vol. 65. No. 1

"Honda Introduces World’s First Collision Avoidance Mitigation System," IVSource.net, June 20, 2003.

"Hitachi Unveils New Radar for Next Generation Eaton VORAD ACC," Ivsource.net, October 9, 2000.

Shladover, Steven E. "PATH Demonstrates Automated Bus Rapid Transit Technologies," California Partners for Advanced Transit and Highways, Online report "Featured Research," Spring 2004. http://www.path.berkeley.edu/PATH/Research/Featured/102803/san-diego.html (accessed April 16, 2004).

Author: Terri O'Connor

April 2004

Last updated April 19, 2004