I found out yesterday that the MBTA have started a trial run of an online feed that provides the current location and estimated arrival times of their eternally wayward buses. Only five routes are represented at the moment - the 39, 111, 114, 116 and 117 - but the feed is freely available, so developers can tap into it and use the data to create pages that can make a decent guess at telling you when your bus is going to arrive. I know of two pages that use it so far:

A live Google map that plots the current location of buses

A next bus ETA predictor (by me!)

If anyone reading this uses those routes and can say whether the pages are at all accurate, and if they work from mobile devices like the iPhone, that would really be appreciated - I can't test them myself yet because the buses for the trial run are nowhere near me. I hope it comes in useful to someone - writing it yesterday caused me to have dreadful nightmares about buses.

Also, if you want to see the service expanded to other routes, you could email the MBTA through their contact page and let them know that there's demand for this kind of service - I contacted them myself yesterday in the hope that encouragement might speed the process up a bit. You never know, it might help.

If you're web-inclined yourself, the XML feed and instructions for accessing it can be found at http://www.eot.state.ma.us/developers/realtime/ .