a method of computing road profiles of various roughness by filtering a random binary sequence is developed; the validity of a simulated profile is established by comparing the generated profile characteristics with the power spectral density of measured profiles and also by making comparison with the specification for construction of motorways. a single wheel laden and unladen, commercial vehicle model is used to examine the dynamic wheel loads generated by types of road which compare broadly with motorway, class a, class b and a profile twice as smooth as a motorway. the simulation results show that over the motorway profile, at vehicle speeds of 64 km/h and 96 km/h, peak impact factors of 1.29 and 1.40 were generated in an unladen model suspension, the values reduced to 1.16 and 1.22 over a profile twice as smooth. in general an unladen suspension produced higher impact factors than when laden. measured results from an unladen lorry taken over a short length of motorway tended to give higher results than the model, but in the laden condition the measured and model results were in good agreement. halving the amplitudes of a new motorway profile reduced the percentage root mean square load above the steady unladen weight by only 3 per cent at 64 km/h and 5 per cent at 96 km/h. the rms dynamic load remains reasonably constant with increased payload.(a)

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