Tuesday, 21 May 2013

Road crashes and smoothing the flow

As this slide from a 2012 TfL survey shows, drivers on London's main roads are much more likely to report delays due to roadworks than due to road accidents ('collisions', more accurately) - but TfL's own data shows that in reality collisions are a much more significant source of delay.
And while delays due to roadworks have fallen, presumably due to a flurry of TfL measures designed to reduce the number and length of works on main roads, delays due to collisions remain stubbornly high and are now more than twice as large as for roadworks. 

So just as Andrew Gilligan has been selling his cycling strategy as a way to reduce congestion, shouldn't we also be seeing a big push to drastically reduce the number of road crashes as a way to 'smooth the flow'?


  1. You mean, like, impose a 20mph speed limit? It is said that every 1mph reduction in average speeds = 6% reduction in collisions

  2. Wouldn't bicycles, by virtue of their greater manoeuvreability, be much less affected by the anti-smoothing effect of works, collisions etc e.g. easier to turn round and use another street than a motor vehicle blocked between 2 others? In this respect, it would be germane to know what proportion of the journeys taken in motor vehicles in this region could have been taken by bicycle, then the potential effect of getting more people on bikes could be calculated. It would also be germane to know what proportion did make the modal shift during the longer-term disruptions. Is it remotely possible that if people simply used bicycles more, both the congestion and flow smoothing problems would be ameliorated?

  3. Great post - important to highlight, as you do, that 20mph limits and safer infrastructure for cyclists (therefore fewer crashes) are actually great ways of 'smoothing traffic flow'.