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What is Intelligent Speed Adaptation?


speed limit sign

Intelligent speed adaptation systems rely on data about local speed limits in order to work.

Image courtesy of John S. Quarterman, via Flickr (Creative Commons 2.0)

Intelligent Speed Adaptation (ISA) is a type of advanced driver assistance system that’s designed to prevent speeding. These systems use a number of different methods to determine the physical location of a vehicle in real time. That location is then matched against the local speed limit, which allows a corrective action to be taken if one is needed. These systems can be either active or passive, which means some merely warn the driver while others are capable of making direct adjustments to the speed of a vehicle.

The Danger of Speed

According to the available data, there is a direct correlation between speeding and an increased incidence of accidents that result in serious personal injuries. According to the NHTSA (PDF), driving either above or below the speed limit increases your risk of being in an accident. Of course, low-speed accidents are less likely to result in serious injuries than high speed-crashes. Other studies have shown that even driving 10 mph over the speed limit can double your chance of being involved in an accident that results in either serious death or injury.

Speeding also has a direct impact on your bank account since it can drastically reduce your gas mileage. According to the University of Missouri, your fuel efficiency can take a 33 percent hit if you speed on the freeway.

How Does Intelligent Speed Adaptation Work?

There are a number of ways to implement an ISA system, and each one is a little bit different from the others. In order for one of these systems to work, it has to have some method of determining where a vehicle is. The four primary methods that ISA systems use are:

  • GPS data
  • radio beacons
  • optical recognition systems
  • dead reckoning

The most common type of ISA system uses GPS data since the infrastructure is already in place. In order for an ISA system to make use of GPS data, it just needs to have a GPS receiver. The ISA system is then able to determine the physical location of the vehicle it’s installed in, which can be compared against a database of local speed limits.

Some GPS navigation units include built-in ISA functionality, though they only work in some areas. When this type of GPS unit is used in an area where speed limit data is available, it will provide a warning if the vehicle goes over the speed limit. Since these navigation units typically aren’t able to receive data from vehicle speed sensors, they typically rely on GPS data to determine vehicle speed in addition to location.

Although GPS data is the easiest way to implement an ISA system, there are a few inherent limitations. Civilian GPS units are far more accurate now than they were prior to the early 2000s, but they still aren’t reliable 100 percent of the time. Even the best GPS navigation unit has the potential for accidentally thinking a vehicle is on the wrong road, and even directly adjacent roads can have drastically different speed limits. If an active ISA system uses GPS data to determine that a vehicle is on a freeway when it’s actually on a nearby surface street, it could potentially accelerate the vehicle to a dangerous speed. The inverse is also true in that a vehicle on a freeway could be slowed to surface street speeds, which could have similarly catastrophic results.

Other ISA systems require significant investments in local infrastructure since they use equipment like radio beacons and optical recognition devices. When a vehicle in one of these systems transits from one speed zone to another, it receives some type of signal from a roadside base station. The driver is then alerted to alter his speed, or the vehicle may automatically speed up or slow down. These systems are less prone to inaccuracy than GPS-based systems, but they are vulnerable to equipment failure.

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