Local, local, local. It’s the new mantra for news. I was reminded of this last week after the train I was riding in struck a pedestrian. The event was insignificant to all but a few hundred, maybe a couple of thousand, people.

There were lots of questions from the people on the train: What happened? Did we kill someone? How long are we going to be delayed? There were also a key question for others who use CalTrain: should I get on the train or find another way home?

Given the small number of people affected, this isn’t the type of thing that makes the local TV news. The Bay Area, being what it is, has a new answer: Twitter. An unofficial CalTrain account allows citizen journalists to share information about what’s going on. Readers can get the news on the Web or by text message.

This kind of real-time journalism has its challenges — initial reports can be wrong. In my own account, I relayed what we heard from the conductor: “On cal train that hit someone. Possible fatal.” The first report on the CalTrain account asks, “Can someone confirm fatality at milbray?” Another report from the field (presumably from someone at the station), said the opposite of what the conductor was telling us: “ambulance is now gone. man is ALIVE. police+firemen still here.”

But these kind of errors occur in mainstream media as well, such as the erroneous reports that most of the Sago mine workers were still alive.

People use Twitter to write about mundane news items: power outages, fires, etc. While they might not be Newsworthy, that are incredibly important to the relatively few people that are affected by them.

Twitter could become the police scanner of our times. As Twitter becomes location aware, it would be possible to detect where something happened by looking for unusal spikes in activity around a location. Even without that, the Chicago Tribune has used Twitter to break news.

Twitter is also getting attention from mainstream journalists. The Washington Post’s media critic, Howard Kurtz, writes about Twitter use by journalists such as Slate’s John Dickerson at the Democratic convention.