I heard a trailer last week for a science programme on the BBC World Service. "Tune in (said the presenter) and I'll explain why physics can explain why, when you've been stuck in a huge tailback on the motorway for twenty minutes, the traffic suddenly speeds up and thins out dramatically for no apparent reason (with no exit roads either)".
I missed the programme, but IS there a scientific reason for this common phenomenon?

It's a shock wave propagating through the 'automotive medium.' Here's an explanation and additional info.

Wow - so there really is a scientific reason. I'm so grateful for this, Priofessor - and so too will my wife when I show her these sites this evening. I'm no science expert, but many thanks!

Colin, did you know that you can usually hear BBC radio programmes after the original broadcast? They are available on-line on the BBC website. The programmes are kept online for a week , sometimes more.It may be yours is still around.Look under radio and then 'archive'for a start, though it may be elsewhere still.

www.bbc.co.uk

Thank you for this Fred. I've had a good hunt around the World Service site, but I reckon I'm perhaps a day or two late for the programme I wanted. This week's version has apparently replaced it. Still, thanks to the Professor I at least have a fully-informed response.