United Kingdom study indicates that Intelligent Speed Adaptation could deliver benefit-to-cost ratios ranging from 3.4 to 7.4, depending on the deployment scenarios.

Results from the UK Intelligent Speed Adaptation (ISA) project

September 2012
Nationwide,United Kingdom

Summary Information

The UK Intelligent Speed Adaptation (ISA) project produced a rich database with high-resolution data on driver behavior covering a comprehensive range of road environment. The field trials provided vital information on driver behavior in the presence of ISA. This paper uses information gathered in the field trials to predict the impacts of various forms of ISA and to assess whether ISA is viable in terms of benefit-to-cost ratio. Three variants of ISA were considered:
  • Advisory ISA which informs the driver of the speed limit and warns the driver when the limit is being exceeded.
  • Voluntary ISA in which the information on the speed limit is linked to the vehicle's engine management system and perhaps additionally to the braking system; the system comes on with the vehicle ignition, but it may be overridden by the driver at will.
  • Mandatory ISA which works like Voluntary ISA, but without the option to override.

In order to investigate the long-term impacts of ISA, two hypothetical deployment scenarios were envisaged covering a 60-year appraisal period:
  • A Market Driven scenario in which users choose to have ISA because they want it.
  • An Authority Driven scenario in which adoption of ISA, particularly "stronger" forms of ISA, is initially encouraged and eventually required.
Following the monetization of the potential benefits, the costs of implementing ISA was also analyzed allowing the benefit-to-cost ratio (BCR) to be calculated.

  • The results indicate that ISA could deliver a very healthy benefit-to-cost ratio, ranging from 3.4 to 7.4, depending on the deployment scenarios.
  • ISA is predicted to save up to 33 percent of accidents on urban roads
  • ISA is predicted to reduce CO2 emissions by up to 5.8 percent on 70 mph roads.
  • Under both deployment scenarios, ISA has recovered its implementation costs in less than 15 years.
  • It can be concluded that implementation of ISA is clearly justified from a social cost and benefit perspective. Of the two deployment scenarios, the Market Driven scenario substantially outperformed the Authority Driven one.
  • The benefits of ISA on fuel saving and emission reduction are real but not substantial, in comparison with the benefits on accident reduction; up to 98 percent of benefits are attributable to accident savings. ISA is predicted to lead to a savings of 30 percent in fatal crashes and 25 percent in serious crashes over the 60-year period modeled.

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How much benefit does Intelligent Speed Adaptation deliver: An analysis of its potential contribution to safety and environment

Author: Frank Lai, Oliver Carstena, Fergus Tateb

Published By: Elsevier

Source Date: September 2012



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Typical Deployment Locations

Metropolitan Areas, Rural Areas


longitudinal control, ISA, Intelligent Speed Adaptation, Intelligent Speed Control

Benefit ID: 2013-00863