The article by Stephen Gray on 40-tonne lorries ("Let's Grow
Page 26
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Up", April 22) prompts me to ask if any of your readers can provide me with any hard figures to show tliat in general a 40-tonne lorry with five axles will not do more damage to the road surface than a 32-ton four-axle lorry. The FTA have not been able to do so.
I know that there is an argument that per ton carried less damage is done by the use of 40-tonne lorries, but I am sure the debate would be more fruitful if there was agreement that in general a 40-tonne lorry is more damaging than a 32-ton lorry.
Stephen Gray quotes TRRL Report No 582 as saying that "40-ton vehicles need cause no greater dynamic loads or vibrations than some existing 32-ton lorries," but the report provides no basis for saying that vibration does not in general increase with gross weight.
What it does show is that the design of the suspension system is of great importance in relation to vibration and that (to quote the report) "the loads and vibrations caused by existing vehicles could be reduced by suitable suspension system design".
The report goes on to say "that increase in weight above 32 tons needinot necessarily result in loads or vibrations greater than those created by many existi.ig vehicles".
However, until good suspension characteristics can be specified in regulations — and the Transport Secretary has said in Parliament that it is too soon to do this — it must be assumed that 40-tonne lorries will in general produce more vibration than 32-ton lorries.
A 40-tonne lorry with a bad suspension system will obviously do much more damage than a 32-ton lorry with a good suspension system.
It would be extremely encouraging to hear that the industry is promoting research into the vibration producing characteristics of