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Transportation Research Group

 

The development of weigh-in-motion sensors and the TRG's Load Measuring mat. Multipl-sensor Weigh-in-motion technology.

In 1986 it was recognised that the standard methods then in use for measuring vehicle dynamics (i.e.

instrumenting individual vehicles) significantly limited the scope of research into road damaging potential.

Each vehicle had to be equipped with extensive and costly instrumentation, and complex data logging and

analysis procedures were necessary. This limited the tests that could be performed to a few specially

prepared vehicles, tested on special purpose test tracks.

It was proposed to instrument the road rather than the vehicle, and the idea of a 'wheel load measuring mat'

was borne. Unfortunately, no vehicle weighing technology, available at that time, was found to be

sufficiently accurate for the requirements of the research. So over the following 4 or 5 years, the

researchers patented and developed a new type of capacitance strip sensor in collaboration with Golden River

Traffic Limited. This sensor has many advantages over other types of WIM sensors - in

particular its low cost, high accuracy, linearity, and insensitivity to temperature, vehicle speed

variations, and tyre configuration.

Two large scale installations of these sensors were undertaken for research into the road-damaging

characteristics of heavy vehicles: one funded by the US Strategic Highway Research Program (SHRP) and one in the UK

funded by the EPSRC. In the UK tests, 155 WIMstrip sensors, mounted in 12mm thick

polyurethane tiles, were installed on the A34 trunk road near Oxford. Over a period of three days of testing,

the dynamic tyre forces generated by some 2000 heavy goods vehicles were recorded. The wheel load data was

analysed to investigate the patterns of wheel loading generated by mixed traffic, and the effects of various

suspension types on dynamic tyre forces.

Load Measuring Mat

Wheel load measuring mat with 150 capacitance strip sensors, installed on the A34 near Oxford

One interesting discovery was that some of the highest dynamic tyre forces were generated by vehicles with

(so called) 'road-friendly' air suspensions. The reason for this apparently anomalous result is that air

suspensions require well maintained shock absorbers to provide their damping - otherwise their bouncing

motion can be lightly damped and they can generate very high dynamic loads. Existing EC regulations for

road-friendly suspensions encourage the use of air suspensions by providing a 1 tonne payload incentive to

operators. However the regulations do not control their in-service dynamic loading performance, or suspension

and damper maintenance. It seems, therefore, that current regulations have the opposite effect to that

intended by the European Commission... In a significant proportion of cases, they increase rather than

decrease dynamic loads and the resulting road damage.

The load measuring mat has also been used to devise strategies for improving the accuracy of WIM systems.

Using arrays of 2, 3 or more sensors, it is possible to compensate for the weighing errors caused by dynamic

loads generated by the vehicles as they 'bounce' over the WIM site. WIM accuracy can be improved markedly.

The researchers have shown that it is possible to measure individual static axle loads with only 5% RMS

error. This compares with (typically) 12-15% RMS error for single sensor WIM systems.

 

Some publications in this area

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Professor David  Cebon
Professor of Mechanical Engineering
+44-(0)1223-332665

Latest news

PhD approved

12 March 2016

Amy Rimmer's PhD dissertation 'Autonomous Reversing of Multiply-Articulated Heavy Vehicles, PhD Dissertation, in Engineering Department' has been approved by the University.

PhD approved

12 March 2016

Graeme Morrison's PhD dissertation 'Combined Emergency Braking and Cornering of Articulated Heavy Vehicles' has been approved by the university.

PhD approved

3 February 2016

Qiheng (Matt) Miao's PhD dissertation 'Vision-based path-following control of articulated vehicles' has been approved by the university.

PhD approved

9 March 2014

Leon Henderson's PhD dissertation 'Improving Emergency Braking Performance of Heavy Goods Vehicles' has been approved by the University.

PhD approved...

25 May 2013

Will Midgley's PhD dissertation 'Regenerative Braking of Urban Delivery Heavy Goods Vehicles has been approved by the University.

Dynamics and Vibrations Group Tea-Time Talks