Lancashire ISA final report: the effect of Advisory ISA on drivers’ choice of speed and attitudes to speeding

  • Published: Institute for Transport Studies, University of Leeds, 2012
  • Authors: F. Lai, S. Jamson, O. Carsten
  • Date Added: 07 Mar 2014
  • Last Update: 07 Mar 2014
  • Format: pdf


To trial the use of Intelligent Speed Adaptation (ISA).


A large number of cars and a smaller number of buses were equipped with an Advisory ISA system based on a commercial satellite navigation system. The system displayed the speed limit and gave visual and auditory warnings as soon as the speed limit was exceeded. A speed limit map covering the whole of Lancashire was prepared. Drivers drove two months without the system active in the baseline condition and then seven months with the system enabled. The drivers were able to drive without the screen being connected, but data on speed and position was still recorded. Data for the full nine months was obtained for 402 cars and 19 buses.

Key Findings:

  • When car drivers chose to use advisory ISA, speeding was reduced by 30 per cent on 30 mph roads and by 56 per cent on 70 mph roads.

  • Being able to use the system (but not necessarily having it active) reduced speeding of the car drivers on 30 mph roads by 18 per cent and on 70 mph roads by 31 per cent. Thus non-use reduced effectiveness but did not eliminate it.

  • For car drivers aged 25 and below, active use of advisory ISA resulted in a reduction in speeding of 22 per cent on 30 mph roads and 37 per cent on 70 mph roads.

  • The effect of system availability on 85th percentile speed was observable but relatively small. This indicates that much of the speeding that was curtailed by the system was in a range that was relatively close to the speed limit.

  • On average, the car drivers were willing to pay around £100 for an advisory ISA system.


Intelligent Speed Adaptation, speed, speeding.