RR697 - In-service assessment of agricultural trailer and trailed appliance braking system condition and performance: The Agricultural Trailer Braking Study

A study was conducted to quantify the service and parking brake performance of a small but representative range of agricultural trailers and trailed appliances in front-line service on UK farms to highlight possible inadequacies in trailer braking system specification and maintenance levels, particularly when used with faster (above 20 mph) tractors.

Braking performance was determined both in 'As-Found' off-farm condition and following maintenance. In 'As-Found' condition, 90% of test vehicles failed to meet UK statutory service brake performance requirements for vehicles travelling no faster than 20 mph, and 40% of parking brakes were inoperative. Following maintenance, 40% achieved/exceeded the statutory requirement and a further 20% approached the required performance level. Nonetheless, 40% of these modern and supposedly serviceable vehicles still failed to demonstrate adequate performance.

Only one example met the requirements stipulated by BS 4639:1987 and the proposed (draft) EU braking regulations for towed agricultural vehicles, either 'As-Found' or 'Post-Maintenance'.

The requirements of existing and future UK and European agricultural vehicle braking legislation are reviewed. The vehicles tested are presented as case studies, considering the need for, and practical and economic feasibility of, upgrading their braking systems to permit safe (and legal) operation at 20, 25 and 30 mph maximum operating speeds. The construction and operation of agricultural trailer braking systems are reviewed and recommendations made regarding selection for typical UK agricultural applications.

Future EU tractor-trailer braking legislation is likely to require significantly greater performance. This can be achieved without undue difficulty or excessive cost, but there is a vital need to raise user awareness and understanding of trailer and trailed appliance braking system specification and selection, to minimise future shortfalls.

The device demonstrating the best performance was to be evaluated over a longer time period in Phase 4 of the work.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.

Assistance in the use of Adobe Acrobat PDF files is available on our FAQs page.

Updated 2021-04-23