The main legal requirements
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REAR underrun bumpers are mandatory on trailers with an intladen weight more than 1,020kg (one ton) manufactured on or after May), 1983.
They are also mandatory* on trucks with a design gross weight of more than 3.5 tonnes manufactured on or after October 1, 198.3, and _first used on or after April 1, 1984.
The main typesofvehicles exempted are tractive units running solo, concrete mixers, rear-end tippers and car transporters. Broadly speaking, the underrun guard must be able to withstand an applied load equivalent to half the gross weight of the vehicle, tip to a maximum of 10 tonnes, sustaining a deflection of no more than 400mm (15.7in).
The bar or beam must be no longer than the width over the rear tyres, but each end of the bar must come within 100,,, in (.3.9itt) of this litaXIMUM width. The rear face of the bar lutist be at least 100mm (3.9in) deep and its bottom edge must lw no more than 550min (21.5in) from the ground.
* Tlw Motor Vehicles (Construction and (Lse): (Amendment) (No 7) 1982. (Amendment) ( No 2) 1983.