According to figures produced by the RHA, the national average price of diesel has risen to as much as 139.60 pence a litre after VAT.
The findings come as part of the latest weekly fuel price survey conducted by the RHA in what represents the most reliable guide to what hauliers pay for diesel deliveries to their depots.
These prices add to the costs for tyres and checks undertaken at any MOT test centre, with safety an important consideration for haulage firms.
Commenting on the rising prices, RHA director of policy Jack Semple said: "This is bad news for customers because haulage rates simply have to keep pace with rising costs."
Mr Semple estimates that the prices now mean that diesel represents around 35 per cent of operating costs for a typical articulated lorry.
He added: "The duty on diesel, already much the highest in Europe, should be reduced in the up-coming Budget."