PACTS Briefing on Intelligent Speed Adaptation (ISA)

Intelligent Speed Adaptation (ISA) is a driver assistance system aimed at increasing compliance with speed limits. Information on the speed limit for the current road is provided in the vehicle and that information can then be used to warn the driver when he/she is exceeding the limit. This is Advisory ISA.

ISA has been trialled extensively in Sweden, the Netherlands, Belgium, Australia, France and most recently the UK.

The following findings are consistent:

• ISA reduces speeding.
• The “stronger” the ISA, the larger is the impact on speeding. Voluntary ISA is more effective than Advisory ISA, and Mandatory ISA is more effective than Voluntary ISA.

The UK trials with ISA had 79 drivers using a fleet of 20 cars fitted with Voluntary ISA. They drove for six months in normal, everyday driving with the initial month as baseline (no ISA), followed by four months with the ISA enabled and a final month with the ISA switched off. Speed and position were recorded 10 times a second, and attitudes were tracked at regular intervals. A total of 355,000 miles with speed limit known was recorded.

The major findings were:

• All groups of drivers (younger/older, male/female, private/fleet) had a reduced tendency to speed with ISA.
• ISA particularly affected the top end of the speed distribution (85th percentile speed).
• There was a statistically significant reduction in speeding for every speed limit except 20mph and 60mph (it should be noted that on British roads there is comparatively little speeding on 60 mph roads).