A professor who specialises in the mathematical and statistical modelling of transport problems is once again challenging data relating to the effectiveness of speed cameras in terms of reducing road casualties.
In December 2015, Mike Maher, an honorary professor at University College London (UCL), challenged camera data produced by TfL, and is now questioning that produced by GoSafe, the Welsh camera partnership.
An article in Local Transport Today (subscription only content) says that a report by the Local Government Data Unit Wales (LGDU) concluded that fixed cameras operated by GoSafe may have reduced fatal or serious collisions (FSCs) by around 46%.
However, when professor Maher used data from 238 sites (61 fixed and 177 mobile) to assess camera effects on personal injury collisions (PICs) and FSCs he reached a different conclusion.
In his ‘Alternative Report on GoSafe Speed Camera Data’, professor Maher estimates that at fixed camera sites PICs fell 28.1% and FSCs fell 13.6%.
Meanwhile, for mobile cameras Maher estimates that PICs increased by 16.4% and FSCs rose 29.9%.
He then combined fixed and mobile data to produce an estimated 2.1% reduction in PICs and a 15.2% rise in FSCs at all camera sites.
The contrasting results appear to be down to different methods used for the two sets of analysis.
The LTT report says the LGDU used a method deployed by professor Richard Allsop for an RAC Foundation report first published in June 2013 and revised in November 2013, while professor Maher used the ‘four time periods’ method to conduct his analysis.
In December 2013 both the DfT and RAC Foundation endorsed the four time period method, which excludes data from the site selection period (SSP) on the basis that it can contain abnormally high numbers of accidents.
We have invited GoSafe to comment on this matter but have not as yet had a response. If we do hear from GoSafe we will add their comment in due course.