Traffic jams - on the tube
A couple of months ago I mentioned the real time traffic monitoring / forecasting site for Nordrhein-Westphalen, which has good forecasts of delays and jams for up to an hour ahead of time.
There are quite a lot of real time traffic services on the web. Did you know, that you can also get a real time view of the disruptions on the London Underground? (Although why Transport for London feels it is necessary to show the date last updated in American format is a mystery to me.)