"It is inevitable that the separation of vehicles will reduce once braking commences. This will occur simply because, in a line of vehicles, any given driver will usually begin to brake only after the vehicle in front has begun to brake, rather than at the same time; thus inevitably there is a lag in successive drivers braking. If separation distances are appropriate the effect has no serious outcome. If following distances are inadequate each driver has to brake slightly harder than the driver of the vehicle in front and, sooner or later, a vehicle somewhere along the line will collide with the vehicle in front."
"Drive at a speed that will allow you to stop well within the distance you can see to be clear. You should • leave enough space between you and the vehicle in front so that you can pull up safely if it suddenly slows down or stops. The safe rule is never to get closer than the overall stopping distance ... • allow at least a two-second gap between you and the vehicle in front on roads carrying fast traffic ... • remember, large vehicles and motorcycles need a greater distance to stop."
"... given the general estimates of vehicle separation provided by the drivers and passengers, and the occurrence of the incident itself, we agree that it is likely that some of the vehicles in the convoy were travelling too close to the vehicle ahead for their speed. Indeed some of the witness evidence describes a separation distance that is closer than that given by the two second rule."