Intelligent speed adaptation

Intelligent Speed Adaptation (ISA) is any system that constantly monitors the local speed limit and the vehicle speed and implements an action when the vehicle is found to be exceeding the speed limit. This can be done through an advisory system, where the driver is warned, or through an active system where the driving systems of the vehicle are controlled automatically to reduce the vehicle’s speed. Intelligent speed adaptation uses information about the area through which the vehicle travels to make decisions about what the correct speed should be. Intelligent systems know when the vehicle has entered a new speed zone, know when variable speed zones are in force (e.g. school zones) and can be configured to work with temporary speed zones (such as at accident scenes or near roadworks). The purpose of ISA is to assist the driver in keeping to the lawful speed limit at all times, particularly as they pass through different speed ‘zones’. ISA is intended to help drivers stick to the speed limit when they are in unfamiliar areas or when they pass through areas where variable speed limits are used.

Types of ISA (Active/ Passive)

The two types of speed adaptation systems, passive and active, differ in that passive systems simply warn the driver of excess speed, and active systems automatically correct the vehicle’s speed. Passive systems are generally driver advisory systems: They alert the driver to the fact that he or she is speeding and allow the driver to make a choice on what action should be taken. These systems can display subtle or highly salient visual or auditory cues, such as auditory and visual warnings. Some passive technology field trails use haptic feedback, wherein the accelerator pedal becomes more resistant to movement when the vehicle travels over the speed limit. Active systems actually reduce or limit the vehicle’s speed automatically by manipulating the engine and/or braking system. Some active ISA systems have been trailed that have an override system so that the driver can disable the ISA if necessary. Active and passive ISA can be used together effectively, or can be used in a system where the user can select between the two.

Speed and location determining/ verification technology

There are four types of technology currently available for determining local speed limits and determining the speed of the vehicle. These are:
* GPS
* Radio Beacons
* Optical recognition
* Dead Reckoning

Global Positioning System (GPS) Receiver based systems

GPS is based on a network of satellites that constantly transmit radio signals. GPS receivers pick up these transmissions and compare the signals from several satellites in order to pinpoint the receiver’s location to within a few meters. This is done by comparing the time at which the signal was sent from the satellite to when it was picked up by the receiver. Because the orbital paths of the satellites are known very accurately, the receiver can perform a calculation based on its distance to several of the orbiting satellites and therefore obtain its position. There are currently 24 satellites making up the GPS network, and their orbits are configured so that a minimum of five satellites are available at any one time for terrestrial users. Four satellites is the minimum number of satellites required to determine a precise three-dimensional position. The popularity of GPS in current ISA and in car navigation systems may give the impression that GPS is flawless, but this is not the case. GPS is subject to a number of fundamental problems. Many of these problems relate to the accuracy of the determined position. The receiver still gets the signal from the satellites, but due to satellites' ephemeris uncertainties, propagation errors, timing errors, multiple signal propagation path, and receiver noises, the position given is inaccurate. Usually these inaccuracies are small and range from five to ten meters for most systems, but they can be up to hundreds of meters. Furthermore, because GPS relies upon a signal transmitted from a satellite in orbit, it does not function when the receiver is underground or in a tunnel, and the signal can become weak if tall buildings, trees, or heavy clouds come between the receiver and the satellites. Current improvements being made to the GPS satellite network will help to increase GPS reliability and accuracy in the future but will not competely overcome the fundamental shortcomings of GPS. In order to be used for ISA, GPS must be linked to a detailed digital map containing information such as local speed limits and the location of known variable speed zones, e.g., schools. Advanced digital maps have the capacity for real-time updating to include information on areas where speed limits should be reduced due to adverse weather conditions or around accident scenes and roadworks.

Radio beacons

Roadside radio beacons work by transmitting data to a receiver in the car. The beacons constantly transmit data that the car-mounted receiver picks up as it passes each beacon. This data could include local speed limits, school zones, variable speed limits, or traffic warnings. If sufficient numbers of beacons were used and were placed at regular intervals, they could calculate vehicle speed based on how many beacons the vehicle passed per second. Beacons could be placed in/on speed signs, telegraph poles, other roadside fixtures, or in the road itself. Mobile beacons could be deployed in order to override fixed beacons for use around accident scenes, during poor weather, or during special events. Beacons could be linked to a main computer so that quick changes could be made.

Optical recognition systems

So far, this technology has been focused soely on recognizing speed signs. However, other roadside objects, such as the reflective "cats eyes" that divide lanes could possibly be used. This system requires the vehicle to pass a speed sign or similar indicator for data. As the system recognizes a sign, the speed limit data is obtained and compared to the vehicle’s speed. The system would use the speed limit from the last sign passed until it recognies a speed sign with a different limit. If speed signs are not present, the system does not function. This is a particular problem when exiting a side road onto a main road, as the vehicle may not pass speed sign for some distance.

Dead reckoning

Dead reckoning (DR) uses a mechanical system linked to the vehicle’s driving assembly in order to predict the path taken by the vehicle. By measuring the rotation of the road wheels over time, a fairly precise estimation of the vehicle’s speed and distance traveled can be made. Dead reckoning requires the vehicle to begin at a known, fixed point. Then, by combining speed and distance data with factors such as the angle of the steering wheel and feedback from specialized sensors (e.g., accelerometers, flux gate compass, gyroscope) it can plot the path taken by the vehicle. By overlaying this path onto a digital map, the DR system knows approximately where the vehicle is, what the local speed limit is, and the speed at which the vehicle is traveling. The system can then use information provided by the digital map to warn of upcoming hazards or points of interest and to provide warnings if the speed limit is exceeded. Some top-end GPS-based navigation systems currently on the market use dead reckoning as a backup system in case the GPS signal is lost. DR is prone to cumulative measurement errors such as variations between the assumed circumference of the tires compared to the actual dimension (which is used to calculate vehicle speed and distance traveled). These variations in the tire circumference can be due to wear or variations in tire pressure due to variations in speed, payload, or ambient temperature. Other measurement errors are accumulated when the vehicle navigates gradual curves that inertial sensors (e.g., gyroscopes and/or accelerometers) are not sensitive enough to detect or due to electromagnetic influences on magnetic flux compasses (e.g., from passing under power lines or when traveling across a steel bridge).

See also

*Intelligent vehicle technologies
* Intelligent transportation system
* Map database management
* Telematics
* Advanced Driver Assistance Systems

External links

* http://www.speedshield.com/main/products/SSV4.aspx
* http://www.speedalert.com.au/faqgeneral_1
* http://users.tpg.com.au/users/mpaine/speed.html
* http://www.isaweb.be/english/ISA-trials/index.html

References

* Basnayake C, Mezentsev O, Lachapelle G and Cannon M (2004) "A Portable Vehicular Navigation System Using High Sensitivity GPS Augmented with Inertial Sensors and Map-Matching", SAE Paper 2004-01-0748.

* Biding T (2002) "Intelligent Speed Adaptation", Swedish National Road Administration.

* Calafell J, Foyer P and Porooshasp K (2000) "Navigation Systems in Europe: Past , Present and Future", SAE Paper 2000-01-1298.

* Carsten O (2000) "External Vehicle Speed Control - Executive Summary of Projects Results", University of Leeds, July 2000.

* Carsten O (2001) "ISA: the Best Collision Avoidance System?", Proceedings of 17th Conference on the Enhanced Safety of Vehicles, Netherlands.

* Carsten O (2004) "ISA - From Fields Trials to Reality", PACTS conference Targets 2010: No Room for Complacency, London, 10 February , 2004.

* Carsten O and Tate F (2005) "Intelligent Speed Adaptation: Accident Savings and Cost-Benefit Analysis", Accident Analysis and Prevention 37, pp.407-416 2005.

* ETSC (2006) "Intelligent Speed Assistance - Myths and Reality: ETSC Position on ISA", European Transport Safety Council, May 2006

* Faulks I (2007) "How fast am I going now? What is the speed limit? Vehicle-based measures to enable drivers to better monitor, manage and control speed: An examination of possible road safety countermeasures", Safety and Policy Analysis International, Sydney, NSW (pending)

* Harsha B and Hedlund J (2007) "Changing America’s culture of speed on the roads", AAA Foundation.

* Hatfield J and Job S (2006) "Beliefs and Attitudes about Speeding and its Countermeasures", Australian Transport Safety Bureau, Report B2001/0342, May 2006.

* IIHS (2002) "Faster Travel and the Price We Pay", Status Report Vol.38 No. 10, Nov 2003. Arlington.

* Kao W (1991) "Integration of GPS and Dead-Reckoning Navigation Systems", SAE Paper 912808.

* Mitchell-Taverner P, Zipparo L and Goldsworthy J (2003) "Survey on Speeding and Enforcement", Australian Transport Safety Bureau, Report CR 214a, October 2003.

* Kloeden C, McClean A,and Glonek G (2002) "Reanalysis of Travelling Speed and Risk of Crash Involvement in Adelaide, South Australia", Australian Transport Safety Bureau Report CR 207, April 2002.

* NHTSA (2005) "Analysis of Speeding-Related Fatal Motor Vehicle Traffic Crashes", Report DOT HS 809 839, August 2005.

* Nilsson G (1993) 'Relationship between speed and safety: calculation method', The Speed Review: Appendix of Speed Workshop Papers, Federal Office of Road Safety, Report CR127A, Department of Transport and Communications, Canberra.

* OECD/ECMT (2006) "Speed Management", Joint OECD/ECMT Transport Research Centre, October 2006.

* Page J (2005) "A Final Technical Report on the Belgium ISA Trial", Belgian Institute for Road Safety.

* Paine M (1996) " [http://idisk.mac.com/mpaineau-Public/Paine_speed_control_0596.pdf Speed Control Devices for Cars] ", report prepared for NSW Roads and Traffic Authority, May 1996.

* Paine M (1998) " [http://users.tpg.com.au/users/mpaine/speed.html#why Why Consider Speed Control Devices for Vehicles?"] , Developments in Safer Motor Vehicles Conference, NSW Parliament, March 1998.

* Paine M, Paine D, Griffiths M and Germanos G (2007) " [http://www-nrd.nhtsa.dot.gov/pdf/nrd-01/esv/esv20/07-0247-W.pdf In-vehicle Intelligent Speed Advisory Systems] ", Proceedings of the [http://www-nrd.nhtsa.dot.gov/departments/nrd-01/esv/20th/esv20.htm 20th International Conference on the Enhanced Safety of Vehicles] Lyon, June 2007

* Peltola H, Tapio J and Rajamaki R (2004) "Recording ISA in Finland", Via Nordica.

* Plowden S and Hillman M (1984) "Danger on the Road: The Needless Scourge". Policy Studies Institute. London.

* Regan M, Triggs T, Young K, Tomasevic N, Mitsopoulos E, Stephan K and Tingvall C (2006) "On-road Evaluation of ISA, Following Distance Warning and Seat Belt Reminder Systems: Final Results of the TAC Safecar Project", Monash University Accident Research Centre, September 2006.

* RTA (2005) "Road Traffic Crashes in New South Wales 2004", Roads and Traffic Authority.

* Wolley J (2005) "Recent Advantages of Lower Speed Limits in Australia", Journal of the Eastern Asia Society for Transportation Studies, Vol. 6, pp. 3562 - 3573, 2005.