Project: Driver Perception of the Performance of the Secondary Braking Systems

Reference: S0025/VD

Last update: 03/12/2003 09:17:58


The main objectives of the project are to:

* determine the number of motor vehicle accidents where brake failure has been reported as the cause of, or a contributory factor to, the accident;
* determine driver reaction to brake failure;
* propose solutions to modify vehicle construction or braking system design to improve secondary brake performance in the event of primary brake system failure;
* propose solutions as to how the driver of a vehicle could most effectively be informed of the existence and operation of a secondary braking system; and
* develop draft proposals for amendments to European legislation to reflect the findings of this research.


Modern vehicle braking systems include an emergency, secondary, braking system to ensure that the driver can brake the vehicle in the event of a failure in the main braking system. However, there is anecdotal evidence that, in accidents where vehicles have suffered perceived 'brake failure', the drivers are not making use of the secondary braking system and believe that the vehicle has no brakes at all. The result being that the vehicle is involved in a collision that possibly could have been avoided.

This perception of total brake failure may be due to a number of issues including the feel of the brake pedal, the lower deceleration possible with the secondary brake system, or simply a lack of understanding of these systems. This research will investigate the extent of the problem and offer solutions, including alternative vehicle/brake system construction and how drivers may be informed of this safety feature.

As part of this research the contractor will carry out tests on a range of subjects using a car simulator and specially modified car to determine driver reaction to brake failure. This will be carried out using a range of drivers of mixed driving abilities and will provide valuable information on driver reaction and attitude to the brake failure.


ICE Ergonomics
Holywell Building, Holywell Way, Loughborough, Leicestershire, LE11 3UZ
+44 (0)1509 283300

Watling Street, Nuneaton, Warwickshire, CV10 0TU
+44 (0)2476 355000

Institute for Transport Studies
University of Leeds, 38 University Road, Leeds, LS2 9JT
Tel: +44 (0)113 233 5325 / 5326

Contract details

Cost to the Department: £224,365.00

Actual start date: 28 August 2001

Actual completion date: 02 October 2003


03-0235036. Drivers' Perception of Secondary Braking Systems - Final Report
Author: MIRA Ltd
Publication date: 02/10/2003
Source: Contact

Summary of results

  1. The results show that all 48 subjects continued to press the brake pedal to try and stop the car when the brakes failed. With a single circuit failure 31 out of the 48 subjects failed to stop within the required distance and, with a vacuum servo failure, 34 out of the 48 subjects failed to stop. However, the vehicle easily complied with the international regulations and to make the regulations more severe would be pointless because the driver would still not be able to stop.
    New technology is developing that would allow vehicle manufacturers to maintain standard vehicle brake pedal feel in the event of system or servo failure, but this technology currently is very expensive and could not be justified in a Cost Benefit Analysis.

    The report recommends that driver education and pre-brake application warning devices are the best way forward. These are very acceptable results.