Superhighways, congestion, and selective statisticsandrewgilliganblogPosted onJanuary 18, 2017Categorie
The transport correspondent of the Financial Times, Robert Wright, has done an interesting post on his blog, challenging what he calls “the now-conventional wisdom among London cyclists that the 12 miles of new cycle superhighways in central London…have had no significant effect on congestion.” As he puts it:
Traffic volumes entering Central London fell 3.4 per cent between the June to September quarter in 2015 and the same quarter in 2016, part of a long-term decline that’s seen the volume of motor traffic entering central London decline by more than 20 per cent since 2000. Instead of increasing with declining traffic volumes, however, average traffic speeds in central London – the easiest available proxy for congestion – fell 3.5 per cent, to 7.8mph.
The figures (from the latest TfL streets performance report) are accurate, but they are also selective. The key indicator of congestion is in fact a quite different measure (also given in the same report) called journey time reliability. It’s the key indicator because it’s not merely a “proxy” for congestion: it measures actual congestion, tracking thousands of vehicles on ANPR cameras and comparing how long they take to make their journeys against how long they should take if the route were not congested.
And guess what? In the same quarter-on-quarter comparison, congestion in central London in fact fell and journey time reliability improved – by 2.1 percentage points in the evening peak and 0.1 percentage points in the morning peak.