Taking advantage of Twitter's real-time aspect, CommuTweet lets commuters share traffic updates, regardless of the mode of public transportation. You can sign in on the CommuTweet Web site with your Twitter account and save your commuting preferences (for example, New Jersey rail) for easy updating that includes the hashtags and commuting codes (#CommuTweet NJR), and choose whether to post to your commute only or the public timeline. Or just do it directly from Twitter. Viewing is the same: go to the Web site, or search on Twitter. CommuTweet is also subscribed to all the official public transit feeds, so there are plenty of updates even if users aren't generating them.
While it may seem like a good use of Twitter, CommuTweet is probably more useful when the transportation is not underground, like most subway systems. With lack of reception, it's questionable how many people would actually remember to update if they can't do it immediately--and doing it later would defeat the real-time purpose. For subways, if delays are an issue, it might be easier to just subscribe to local transportation authority's feeds.