I finally got a response to my FoI request to the Highways Agency. They're sorry, but they have to postpone answering until 26th November, because I asked for so much stuff.  Ho hum.  This (while legal) takes the date past the media interest window which started with the removal of the bus lane yesterday morning and probably ended when Prince William's engagement was announced, and thus no one will notice.  Since the original quoted date for removal was 24/12 it's a bit strange that it's all been done in a rush just as the evenings are closing in and the weather's turning nasty - the first morning was blissfully clear due to, er, the M4 being closed at Slough due to a crash.

Anyway, what can we deduce?  Well, I've not travelled the route in either direction yet (next week sometime I will) but a combination of Google Traffic and Traffic England along with monitoring Twitter gives us some impression.  

  • Last night at about 19:17 Google Traffic had the road red from Heston to the 3>2 merge.  
  • Tonight at about 19:19 Google Traffic has the road red from Heston to the 3>2 merge.  

I'm seeing a bit of a pattern here, but it's early days.  Tentative conclusions:

  • Traffic now seems to go fast/very slow instead of steady
  • There's a massive long-lasting slow peak persisting past 8pm
  • Jams seem to start at J1 and spread backwards and at Heathrow
  • Jams once started take a very long time to clear

There's an extra stat we can measure - because the Traffic England site allows you to monitor average speeds from junction to junction, taking a reading every few minutes and finding out the distances between junctions gives us the transit time (average speed/distance = average time).  Here's the table - cumulative transit time on the right (note: doesn't try to allow for the fact that it takes time to traverse each section, that's a bit harder mathematically, but it does indicate when the whole route is slowest and crucially what the steady state low traffic transit time is - about 16.5-17 minutes from J6 to J1):


Day Time Duration
17/11/2010 17:12 21.4
17/11/2010 17:25 24.7
17/11/2010 17:38 29.2
17/11/2010 17:45 28.8
17/11/2010 18:07 29.6
17/11/2010 18:19 28.3
17/11/2010 18:25 28.7
17/11/2010 18:34 29.3
17/11/2010 18:40 30.0
17/11/2010 18:49 29.1
17/11/2010 19:04 28.7
17/11/2010 19:18 41.8
17/11/2010 19:30 48.3
17/11/2010 19:48 59.5
17/11/2010 20:03 54.6
17/11/2010 20:18 40.3
17/11/2010 20:25 38.0
17/11/2010 20:33 36.0
17/11/2010 20:43 22.0
17/11/2010 20:50 19.9
17/11/2010 21:03 16.8
17/11/2010 21:17 16.7
17/11/2010 21:30 17.0
17/11/2010 22:02 17.4

I'll keep monitoring this until the FoI result appears.

P.S. in case anyone's worried about the reliability of using commercial traffic services to analyse stuff best left to professionals, I'm unreliably informed that Phil Hammond's snap decision might have involved data from a certain manufacturer of navigational equipment.