Why scrapping the M4 bus lane is bad for motorists

I’m no stranger to the M4 and the bottleneck around the bus lane at Junction 3, getting back into London is infuriating. The news been somewhat drowned out by benefit changes but Phil Hammond’s shamelessly populist announcement that the M4 bus lane will be scrapped is going to make things worse, not better.

The rationale for the M4 bus lane is poorly understood – and not helped by New Labour spinning it as an environmental measure when it was, and remains, primarily an important traffic management technique.

The reason there is a bottleneck on the M4 is that between junctions 3 and 2 the road reaches on elevated section, just two lanes wide on each side, and with a 40mph limit. It’s not hard to see that this would cause a bottleneck at the head of the a 70mph motorway with 3 lanes and a hard shoulder on each side. Widening the final section of the M4 is impractical/expensive/politicallly “brave” as widening an elevated motorway in London involves requisitioning and demolishing so much private property.

So the Highways Agency came up with a simple, yet ingenious measure. In order to manage the flow of traffic better they brought the narrowing of the road forward to junction 3, when much traffic is leaving the M4 anyway, and dropping the speed to 50mph (since raised to 60mph). That left them with a “spare” lane and rather than painting it with white lines (or planting trees or whatever) they decided to paint it red so that the few busses and taxis on the M4 could take advantage – and why not? Of course, the bus lane is under-utilised, if it wasn’t it wouldn’t solve the bottleneck!

Although the bus lane reduces the space available on the road it smoothes traffic flow: the well-respected Transport Research Laboratory’s research showed that despite increased traffic, peak-time journey times were actually reduced for all vehicles; off-peak times did go up slightly for cars, but all journeys were more reliable.

For more detail, including a graphical explanation on the M4 bus lane, see Chris Marshall’s explanation.

Phil Hammond’s announcement may well earn him some brownie points for seeming to oppose an “anti-motorist” measure. Yet the real anti-motorism here is this surrender of logic and evidence-based policy to shamless populism.

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