If you've never taken a look at the NextBus.com service you should. It's one of those resources that's not only very useful (if it's available in your area) but also very cool. It's also another example of real-time info on the web.
NextBus describes precisely what this free service offers. Users can click and find out when the next bus, train, water taxi, etc. will arrive at a specific location. As you've probably already figured out, NextBus uses GPS technology to predict when a vehicle will arrive at a specific location. You can learn more about how the technology works here.
Since online mapping is all the rage these days, you'll be happy to learn that NextBus also provides live maps that allow you to quickly visualize the current location of a vehicle.
I wouldn't doubt that one of these days we'll see one of the large online service like Yahoo, MapQuest, or MSN work with NextBus (and other providers) to make this real-time info available on their map products. Actually, I'm somewhat surprised that we haven't seen this already.
An e-mail alert service is also provided that notifies you when you're bus/train/water taxi is about to arrive. Cool!
Since you might not be always in front of a computer but still want to know when the next vehicle will be arriving, NextBus also offers a mobile version of the service.
NextBus is not the only real-time transport info service out there.
Finally, I'm sure many of know you can also track aircraft in the US/Canadian system in real-time. For example, this service allows you to track commercial flights from many airlines and then places the info on a map. Simply reload for the latest info. Want to track a plane from a mobile device? Here's one service that I use.
Postscript: On a related note, this CNN article takes a look at a new
SMS (text-messaging) service in the UK that offers real-time flight info. What the article doesn't mention is that both 4info.net and Synfonic are two US-based SMS services that provide real-time flight info.