The effectiveness of the braking systems on new vehicles is controlled by well-developed international legislative requirements. Many disabled drivers use vehicles which they are enabled to control by the addition of special devices. These devices are not subject to any required standard and there is little empirical data regarding their performance and effectiveness. There is therefore no background for testing their safety or for assessing improvements in their design and little research has been done to establish how well they work. As a result, the DTLR has sponsored research to compare the braking performance of standard vehicles against the same vehicles adapted for disabled drivers, to ensure that safety is maintained. In this investigation, a range of device types has been tested both for effectiveness in actuating the vehicle braking system, and effectiveness in use with respect to human factors. From the tests it was found that several of the devices were unable to match the braking performance obtainable through use of the vehicles’ conventional controls. With the full brake systems functioning, all the systems were capable of achieving the minimum stopping distances required by international legislation. However, with a partial braking system failure, four out of five of the mechanical adaptations were unable to provide sufficient braking performance in all the vehicles tested. It was found that the lack of effectiveness was very dependent upon the installation, and that adaptations that worked well on one vehicle failed to work effectively on another. Driving trials were undertaken, during which 12 non-expert drivers undertook a range of normal driving manoeuvres in a Renault Scenic with each of the adaptation types. Drivers’ emergency stopping distances were significantly increased when using three of the control adaptations. The portable type control did not permit the driver to achieve the same levels of deceleration, and stopping distances were on average four metres longer (from 40mile/h). This is probably due to the control not being attached to the vehicle at the upper end of the control, allowing it to move forward when the driver applies high forces. The control in which the brake is applied by pushing the lever, and the throttle by rotating it (i.e. independent throttle and brake control) also had significantly longer emergency stopping distances (five metres). This may be due to the need to move the control in two planes to reduce acceleration and then apply the brake. The other manual and the electronic control both permitted drivers to match the stopping distances of the standard (foot) brake. The trials also found that the electronic controls required more ‘input’ from the driver. Deceleration variances showed that drivers made more adjustments to the brakes as they attempted to slow to a stop line under normal braking conditions. This is evidence of the effects of the reduced control feed and feedback provided by these ‘remote’ controls compared to the manual controls which attach directly to the conventional pedals. The report makes a number of recommendations for the design, development and installation of braking adaptations. With regard to electronic controls, further development is required to optimise the control characteristics. It is important that drivers of electronic controls be provided with adequate training, not only for their and other roads users’ safety, but also to ensure that a lack of confidence does not effectively deny them access to this control option. A number of recommendations are also included in this report, relating to general design principles and additions to the codes of practice for installations and training. (Author/publisher)
Abstract