Queuing

I’ve been meaning to write a bit more about the M4 bus lane, but haven’t had the time, so here’s a rather crude brain dump while I sit in the dark on a bus somewhere on the A9 in the snowy Cairngorms.

The Dutch infrastructure minister recently announced that speed limits on some stretches of motorway would be raised.  This would not help Motorists get to their destinations any quicker, she noted, but it was a change worth making because it would make the motorists feel better.  Aside from being a delightfully refreshing piece of honesty from a politician, it highlights again that behaviour and psychology should not be ignored when designing transport policy.  Philip Hammond should have been this honest when abolishing the M4 bus lane — instead of the weak nonsense about improving journey times, just tell the truth that it’s a cheap way of making Motorists feel better.

The M4 bus lane was designed to cut the journey times of Motorists entering London — to make their journeys faster and more reliable, and thus to cut the <insert absurd made up number here> billions of pounds that the Institute of Directors like to claim is lost because of their Jags being caught in congestion their supply chain being delayed by congestion.  The Motorist probably thinks that he too would like his journeys to be faster and more reliable.  But this is not quite true.  The Motorist would like his journeys to seem faster and more reliable.

The M4 bus lane was hated not because it increased car journey times or made journeys less reliable.  It didn’t.  As previously explained, the bus lane was a clever hack to the layout of a road with a bottleneck.  It made a tiny and irrelevant cut to journey times, while cutting lane changing and accident rates and thus greatly improving consistency in journey times.  The bus lane was hated because motorists thought it increased their journey times.

Part of it was the problem of common sense.  The likes of Jeremy Clarkson and Terry Wogan despise those scientists and academics with all their fancy facts and data — the problem with these researchers is that they don’t have any common sense, and common sense tells Clarkson and Wogan that taking away one lane of the M4 must have caused traffic jams.  No amount of your facts can change that.

Another part of it was recall bias: all of those massive pre-bus lane jams begin to blur into the distance, whereas this jam that I’m sat in right now is real — and hey look, there’s a bus lane.  Coincidence?

But it was more than this.  It was about people’s perception, and particularly people’s perception of queues.  Since I’m on a bus with no reference material and limited battery life, I’ll put it in bullet points:

When sat on a Motorway in a traffic jam, Motorists usually believe that their own lane is going the slowest.  It’s simple: when their own lane is moving freely, they’re concentrating on driving, and don’t notice that the other lanes are stationary; when their lane is stationary, they have nothing better to do than stare at all the vehicles which are moving freely in the other lanes.  So even if over time all lanes even out, the Motorist perceives that the other lanes are moving better — especially if the jam is severe enough that they spend more time stationary (observing others moving) than moving themselves.   (Hence all the futile changing of lanes in jams, which just makes the jams worse.)  This is the same reason why in the Post Office — wait, do blog readers even still use those?  OK, this is the same reason why in the ticket office at a major station, you have a single queue serving several windows, rather than independent queues.  Independent queues make people nervous about their decisions.

This perception leads to Motorists overestimating their time sat in traffic, and it’s made worse when they can see moving traffic — if the opposite carriageway is moving freely, or there’s a parallel un-jammed road, then the sight of moving cars merely serves to remind the poor stationary Motorist of their own lack of motion.  Drivers asked to estimate how long they were stuck in traffic consistently over-estimate the jam if they see other traffic moving freely.

So the M4 bus lane was about the worst thing you could do if you wanted Motorists to perceive that they were spending less time in queues.  Now when they were sat in a queue they weren’t just sat there with nothing better to do than get paranoid over the relative speed of the two lanes of traffic: they could also sit there watching the buses and taxis and prime-ministers go past at speed, constantly highlighting the fact that the Motorist was going nowhere.

The research shows this — have drivers estimate their queuing time with and without visible moving traffic nearby; or compare the driver and passenger experience of a stop-start motorway jam. It’s just another of the many fascinating little quirks of psychology — one of the bizarre things our brains do when confronted with absurd man-made situations like traffic jams.  You can make Motorists happily spend more time sat in traffic jams, simply by making them sincerely believe that it is less time.

(Somewhen I’ll try to find some interesting references, but 3G has just dropped out…)