Chris Polack's letter on the Essex lorry crash, (NCE 18 July), rightly draws attention to the vehicle element of this incident. A glance at the pin device securing cab to trailer of articulated vehicles suffices to show it is inadequate to prevent separation when the cab is abruptly twisted in the vertical plane relative to the trailer unit.
However, the problem goes deeper. In all full scale Motor Industry Research Association (MIRA) tests to validate the designs of BS6779, the rigid body tanker rose up on to the parapet top with body mass overhanging the outer face.
This is with a vehicle centre of gravity at 1.73m above road level and parapet height of 1.5m - there are rigid body vehicles with centre of gravity more than 2m above the road.
Of even more concern in the MIRA tests was that while the tanks were not ruptured, water ballast was ejected from the pressure relief valves. With volatile liquids the potential serious consequences of such an arrangement need not be stressed.
Colin Tucker (M), The Anchorage, 42 Park Lane, Sandbach, Cheshire, CW11 1EW