On Sun, 15 May 2005, Dave Arquati wrote:

Tom Anderson wrote:
On Sat, 14 May 2005, Dave Arquati wrote:

Tom Anderson wrote:

On Thu, 12 May 2005, Dave Arquati wrote:

A very impressive system would be to not only have accurate
Countdown information online and at stops, but also to have
dynamically-estimated journey times to destinations from that stop,
available both online and via Countdown at the stop itself.

Yes, this would be very cool, but the amount of effort it would
require to gather the traffic data, process it to produce congestion
forecasts (not entirely unlike weather forecasting - congestion is a
dynamic, nonlinear, mobile phenomenon), work out delays to services
and distribute this to every bus-stop would be substantial.

I don't (think I) mean forecasting congestion, as such... just using
data on current traffic speeds to estimate those journey times.

Ah, but that does involve forecasting - if you want to know about
delays that a 38 at Victoria might suffer when it gets to Hackney, you
need to have some idea of what the traffic is going to be like about 45
minutes into the future.

I don't think that's entirely necessary (although it would certainly be
impressive!). Knowing about existing delays on the route will give
vastly superior realtime information to that currently available - so if
congestion is already occurring in Hackney, it would be highlighted at
the 38 stop at Victoria, on the assumption that congestion tends to
clear slowly.

Okay. I'm dubious about this; it will warn people about problems that
won't affect them, and fail to warn them about problems which will.
However, it's better than nothing, which is what we have now.

There's a case to be made that it's better than forecasting - forecasting
necessarily means telling people things you don't know to be true, but are
basically guesses. Telling them possibly irrelevant truths is
straightforward and honest, even if it does lumber them with more
working-out to do themselves.

One crucial quantitative factor is the volatility of congestion; if the
typical lifetime of congestion is longer than the length of the bus's
route, then it's worth telling peole about congestion that's occuring now.
If it's not, it isn't. And i don't know if it is.

On the flip side, it's quite likely TfL are already doing this
forecasting as part of their realtime congestion management work.

I wonder how they would do it. Weather forecasting involves predicting
movements of fronts and such (although I know very little about it!),
but congestion forecasting would seem more difficult as it can arise
much more spontaneously - e.g. if a lorry breaks down in an awkward
location.

True. However, congestion that's not related to accidents might be
predictable, and the degree to which an accident could generate congestion
(congestion potential, if you will) might be.

Maybe I should make this my Masters project next year... I know a couple
of friendly computing/information systems students who might like to
collaborate!

Please do.

No, wait! I never uses buses - work on something to do with tubes or
bikes. Cheers.

tom

--
People don't want nice. People want London. -- Al