Clusters of Accidents Sometimes Just “Bad Luck”
In a recent article about the evaluation of the effectiveness of speed cameras saving lives, the UK Telegraph quoted Dr. Linda Mountain, Department of Engineering at Liverpool University:
“Speed cameras do reduce accidents but not quite as much as has sometimes been claimed.”
“I think it’s not reasonable to say that 100 lives a year are being saved.”
“The number has been overestimated by 50 per cent on the basis of our data. Nevertheless, that’s a worthwhile saving.”
Dr Mountain said the assessment methods used by the Government and police authorities to evaluate speed camera success failed to take account of random “bad luck” at notorious accident spots.
She said that clusters of accidents are not always caused by dangerous roads and can be caused purely by chance, which would mean the number of accidents would have fallen regardless of whether a camera is put there or not.
The study forming the basis of the Government claims looked at accident trends of all 4,100 camera sites in the UK.
It found that over a period of four years speed cameras were responsible for a 22 per cent drop in the number of accidents.
The number of people killed or seriously injured was said to have fallen by 42 per cent, amounting to around 100 lives.
Dr Mountain, however, re-examined the evidence, conducting a new study looking at road accident numbers before and after cameras were installed at 215 sites.
She used an alternative analysis method, which took into account the element of uncertainty, resulting in a 19 per cent reduction.
Not allowing for this element would have indicated a reduction of 50%.
Dr Mountain added:
“If accidents fall dramatically after the cameras are in place, it could be that the cameras have reduced accidents – but some of the fall may simply show that a run of bad luck has come to an end.”
How do you measure the improvements of you performance improvement efforts?