Austroads Freight Taskforce (2014-2015)
Use of Auxiliary Brakes in Heavy Vehicles
The purpose of this research was to review the current use of auxiliary brakes operating on very long and steep descents and recommend safe, appropriate and adequate measures to improve road safety and amenity.
Road safety objectives include:
- Developing a better understanding of driver awareness and behaviour in regard to the correct use of auxiliary brakes
- Development of an operator check-list that will encourage safer driving on steep downhill grades through the correct use of auxiliary brakes
- Determining what the maximum speed limit(s) should be for heavy vehicles on steep downhill grades if a differential speed limit were used instead of a low gear sign.
Australian road authorities commissioned this research into the correct use of auxiliary brakes on heavy vehicles in response to a number of serious incidents involving runaway trucks on very long, steep grades and continued noise complaints from the community. Their objectives were related to both safety and amenity and included:
- developing a better understanding of driver awareness and behaviour in regard to the correct use of auxiliary brakes
- development of an operator checklist to encourage safer driving on steep downhill grades through the correct use of auxiliary brakes
- determining what the maximum speed limit(s) should be for heavy vehicles on steep downhill grades if a differential speed limit were used instead of a low gear sign
- developing a better understanding of the current strategies and approaches for auxiliary brake use in residential areas
- developing an understanding of the attitudes of heavy vehicle drivers and local councils to auxiliary brake use in residential areas and driving strategies used to reduce the impact of noisy engine brakes.
The research included a substantial literature review of previous studies related to auxiliary brake systems, crash statistics, brake noise, vehicle standards, brake system maintenance and future technologies. Surveys of truck drivers and local governments were also undertaken and a field testing and simulation program was designed and run to assess differential speed limits on long steep grades.
Many important learning outcomes are presented in this report; however, the following outcomes and recommendations require particular attention and consideration:
- There is a lack of driver training on the use of auxiliary braking systems even though drivers who have received training have indicated that it is very useful. A driver training framework has been proposed which includes elements of safe, efficient and polite driving.
- The research suggests that noisy engine brakes have potential health implications, particularly when people are sleeping. However community concerns in relation to health risks are isolated and localised. While a national regulatory approach is soon to be implemented, measures to address noisy engine brake issues, in particular noise cameras and sound barriers should be targeted at areas where community concern is the greatest.
- Differential speed limits for heavy vehicles are both feasible and effective in reducing the risk of service brake fade. A framework for assessing differential speed limits based on end of slope brake temperatures and computer simulation has been developed. It shows good alignment with field test results and experience in reducing runaway risk for large heavy vehicles on steep descents.
- This framework can be readily applied to other steep descents both to assess appropriate heavy vehicle speed limits and also to support restricted access vehicle determinations.
- Australian regulators need to consider mandatory auxiliary brake system performance requirements for certain categories of heavy vehicles. While the Economic Commission for Europe (ECE) endurance braking system requirements would serve as a useful framework for assessing brake system performance, it is likely the performance limits would need to be specific to Australian conditions. Performance requirements may need to be incorporated into both the Australian Design Rules (ADRs) and the Performance Based Standards (PBS) Scheme.
To access the full report, click here.