NextBus

NextBus

One evening Morgen and I were at a dreams group meeting way across town. The most direct route home was by way of San Francisco’s MUNI light rail line, but as we approached our stop, we saw that we had just missed a train. Knowing how infrequently trains tend to run late at night, a friend who was waiting with us wondered out loud how long we might have to wait for the next one, and whether we should consider finding an alternate route. I pulled my cell phone out of my pocket, and after a few clicks on the keypad, I announced: “ Looks like11 minutes.” We decided to wait. Sure enough, exactly11 minutes later, the train arrived. This little trick came courtesy of a high- tech service called NextBus.

Location, Location, Location

The idea behind NextBus is sophisticated yet elegant. Every vehicle on a transit line is equipped with a rooftop device that contains a Global Positioning System( GPS) receiver and a radio transmitter. The GPS receiver constantly tracks the vehicle’s exact location by satellite. This information is transmitted to a central computer, which calculates the amount of time it should take that vehicle to reach its next several stops, based on its current speed, typical travel time, and other variables. These predictions are continuously recalculated, so that even with delays, traffic, or detours, the estimates remain highly reliable. The information is available in real time via the Web and can be viewed using the built- in browsers on most cell phones and PDAs. In addition to time estimates for particular stops, you can even see a live map showing the locations of all the vehicles being tracked. Digital displays are also posted at some bus stops and shelters for added convenience.

Municipal governments and transit agencies subsidize the NextBus service— which is free to users— as a way to reduce frustration among riders. Knowing when the next bus is going to arrive can help you plan your schedule, avoid spending unnecessary time in the rain, and travel more efficiently. NextBus is also extremely useful for route planning. For example, there are usually several ways to get from place to place in San Francisco. If I know that a train won’t be coming for a while, I can opt for a subway or bus instead— perhaps more walking, but a shorter overall travel time.

Can You Track Me Now?

Of course, NextBus is far from perfect. I’ve seen the system predict the arrivals of trains that never came, and I’ve also been told the next train was45 minutes away only to have one roll up the next minute. One of the reasons for the inaccuracies is that transit systems sometimes switch trains between lines for one reason or another. If a train from line A happens to be on track B, the system doesn’t know what to do with it, because it can’t tell what route it’s ultimately going to take. The tracking devices are also subject to electronic failure, and can sometimes get out of sync when going through tunnels. Then there’s the fact that the computer needs a certain amount of history in order to perform a calculation. I live near the beginning of a certain transit line; the first stop is only three minutes away. So when I ask NextBus when the next train is coming, it often gives a wildly inaccurate prediction20 minutes or so in the future, based on the average departure times of the trains. A few seconds later, though, the prediction may become“3 minutes.”

The NextBus service is currently deployed in dozens of different transit agencies across the United States and England, and is expanding into Canada. However, some agencies still have only limited coverage. In San Francisco, for example, where all the light rail trains have tracking devices, only a tiny percentage of the buses do— even though the service has been in place since1999. And in some other cities, the service is still in a pilot or demonstration stage, awaiting approval or funding for a full roll- out.

Still, NextBus is a textbook example of technology as it should be— useful, accessible, and simple. Unlike regular trains, the buses and rail lines that use city streets have no hope of running on a strict and reliable schedule. Although NextBus won’t make them arrive sooner, it keeps riders happier while they wait