I have been researching the merits of installing road humps. In this process I came across your article (NCE 25 September 2003) and the responses of the 500 engineers that you asked to comment on the effects of speed humps on road safety.
From my recent review of available reports on the subject I can only assume the 51/48% split is based on personal preference and not evidence.
The Transport Road Research Laboratory has carried out numerous tests on traffic calming methods including speed humps. All, when correctly installed, reduce the speed of vehicles.
This is confirmed by the Emergency Services complaint that response times are increased.
Unfortunately in my research I was only able to find one TRL report that analysed accident reports before and after the installation of traffic calming measures. This is TRL452 covering 56 villages analysing fatal/serious accidents which states 'accidents have undergone significant reductions, ahead of national trends'.
It is clear to me that insufficient attention has been paid to analysing accident statistics before and after installing traffic calming measures. This is one reason why engineers appear unable to speak on this topic without personal prejudices dominating every discussion.
Reg Humphries (M), 9 The Green, Ewell, Epsom, Surrey, KT17 3JS