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Active Speed Limiters

By: Sally Aquire - Updated: 6 Sep 2012 | comments*Discuss
Active Speed Limiters

Many road traffic accidents are caused by drivers failing to respect the speed limit, and being unable to react if an unexpected situation occurs. This is the case in 29% of accidents. Some cars are now fitted with active speed limiters that do not allow you to go above a certain speed in a bid to reduce the number of speed-related accidents. Their main benefit is to make sure that you do not break the speed limit, as they physically restrain you from doing so.

Active Speed Limiters Work?

Active speed limiters work by keeping an eye on your vehicle's speed. They are not able to stop you from exceeding speed limits though (see the following section on ISAs for information on that).

They can be useful driving aids though, as the speed limit is not always the same across all vehicles. If you drive a van or bus, you are legally obliged to have a speed limiter fitted to your vehicle (depending on the size of the bus or van) to make sure that you do not exceed the speed limit for these types of vehicle (56 mph for goods vehicles and 62 mph for buses). For car drivers, they are optional, but they can make driving a lot safer.

Some cars are fitted with a different type of active speed limiter, which allows you to select your own maximum speed limits. They work in the same way, as they do not allow you to exceed your pre-selected speed limit. The drawback of this system is the need to already know the speed limit before you set off, whereas the usual active speed limiters do the hard work for you. This type of active speed limiter can often be found in Jaguar cars.

Intelligent Speed Adaptation

Intelligent Speed Adaptation (ISA) uses Global Positioning System (GPS) technology to locate the precise location of the vehicle. Using this, it can get information about maximum speed limit on the road that you are currently driving on. If you have one of the more advanced systems, once you have reached the maximum speed limit, you cannot go any faster. You can keep pressing the accelerator, but it will not have any effect on your speed.

There are three types of ISA:

  • Advisory: This type of ISA only alerts you to the recommended speed limit and informs you when you are about to exceed it
  • Voluntary: This type of ISA actually stops you from exceeding the speed limit and is connected to your vehicle controls. In many cases, you do have the choice of ignoring it
  • Mandatory: This type of ISA also stops you from exceeding the speed limit but there is no element of choice here - you must obey it

There are also three types of ways in which ISAs gather their information and relay it to you:

  • Fixed: These inform you of general speed limits
  • Variable: These inform you of situations in which the speed limit is lower than normal, for example at pedestrian crossings
  • Dynamic: These also inform you of temporary speed limits that are put in place due to weather conditions or accidents

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