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Task Force reports on trailer failure
Page 133
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• DOES the rising trend in Department of Transport test failure rates for trailers over the past few years reflect a progressive decline in maintenance standards? Probably not, according to the interim report of the Trailer Task Force set up by the DTp following concern at the annual test fail rate.
It seems likely," says the in terim report, "that the trend is due to the combined influence of events over the last few years, unconnected with maintenance standards, that have affected the difficulties."
The Task Force, led by chairman Eric Dunn, says it is often assumed that trends in failure rates at annual tests reflect the condition of vehicles in service. However, there is at present no separate comprehensive information readily available that reflects in-service condition of different categories of vehicle.
The Task Force, in making nine recommendations, concludes that consideration should be given to regular surveys of the condition of a randomly selected sample of goods vehicles in use. The other proposals are: 1, Ministry plate requirements be made a condition of acceptance for test (instead of part of the test).
2, "Secondary brake performance" for trailers be deleted if an adequate method can be determined to ensure all features of the trailer brake system operate satisfactorily.
3, Efforts to develop a method of testing the brake performance of unladen vehicles be endorsed.
4, Explore relating more closely service brake performance requirements to design parameters for certain trailers where European Community requirements reduce the maximum allowable brake force.
5, Explore the scope for provid ing more trailer service brake force within the upper limits imposed by EC Directive requirements.
6, Refine the analyses of roadside check and fleet inspections.
7, Consider some form of advice to operators on good maintenance practice.
8, Research reasons for failure, in order to help operators in their preparation of vehicles for test.
In an annex to the report, the DTp's Vehicle Inspectorate says that its 1987/88 annual report for the second year running highlighted concern at increasing trailer rate failures. Over the period 1983/4 to 1987/8 it increased steadily from 14.4 to 18.8%, while that for motor vehicles remained approximately static.
One area of particular concern, it says, is the requirement for trailers built since October 1982 to meet the EC comparibility requirements of directive 75/524.
In its executive summary, the Task Force says the most significant factors affecting the trailer failure rates are associated with their brake systems. But the rising trend may be more related to events during 1983-1988 than to a decline in the condition of trailers presented for test.
The Task Force cites the introduction of the EC braking directive tractor/trailer compatibility requirements, and the increase in the annual test service brake levels. While providing for safer levels of brake force on the road, It says they may make it more difficult to achieve pass levels under heavy goods vehicle test station conditions.
Also, says the Task Force, more three-axle trailers with more complex brake systems, are coming on the road. The report adds: "It is clear that the way in which some trailers are operated makes it more difficult for them to he regularly maintained than motor vehicles." The 10 most frequent causes of failure are above.