It’s one of the most irritating experiences a bus rider can have: After standing on the side of the road for 15 or 20 minutes, the bus finally comes plowing up to the sidewalk — followed almost immediately by another.
“I’m waiting, waiting, waiting, and then I see one right after the other,” said Tyler Sousa, a high school student who commutes through Revere on MBTA buses. “And I’m like, ‘What the heck?’ ”
The phenomenon, called “bunching,” is common across the Massachusetts Bay Transportation Authority bus system, sometimes afflicting the subway as well, an intractable transit problem that MBTA officials say they are trying to address but will have difficulty eradicating.
They say they can tinker with dispatching strategies and develop better methods for adjusting vehicles to make space between them, but that, of course, tends to annoy the passengers on those vehicles.
But the biggest thing the T can do to cut down on bunching is improve overall service. Unlike many issues plaguing Boston’s transit system, the bunching of passenger vehicles is not directly attributed to the age of track equipment or trains or buses. Instead, it’s a consequence of the delays that haunt the system for any number of reasons: traffic, crowding, or some form of mechanical issue. Nor is it unique to the T; most transit systems in the world struggle with the problem, especially on buses. In London, it was even the subject of a 2009 novel — written, naturally, by a bus driver.
“This has cursed every place, and people have very strong feelings about it,” said John Bartholdi, an engineering professor at the Georgia Institute of Technology.
Imagine a bus stuck in traffic at one tricky intersection, falling more and more behind schedule with each turn through the traffic signal. Meanwhile, passengers crowd at the next stop as they await the now-delayed bus. By the time it finally arrives, they all jam onboard, some paying in cash and others struggling to squeeze on or off the bus, a long process that makes the delay even worse. And as that process repeats itself down the entire line, there are fewer passengers boarding the following bus, letting it creep closer with each passing stop.
“You may start them off equally, but there are forces of attraction so that anytime one of these gets a little closer to the other, the force gets stronger,” said Bartholdi.
MBTA deputy general manager Jeff Gonneville said several initiatives at the T could help fight bunching problems. Most of them are geared toward tackling delayed buses, such as the sudden proliferation of bus-only lanes on city streets and new fare technology that will end time-consuming cash payments on board buses and trolleys. Newer T buses also have slightly more floor space, making it easier for passengers to board and unload around strollers or other push-carts.
The bus lanes, in particular, not only minimize delays, but also allow drivers to tell waiting passengers they can’t board but that another bus is coming soon, with confidence that it won’t get caught in traffic. That would probably annoy those riders, but would help re-establish spacing and improve overall service on the line.
“Those are the kinds of mid-trip adjustments we can make, and having the dedicated lanes gives us the flexibility and ability to run more efficiently,” he said.
On the subway, where delays and crowding can cause similar bunching problems and trains occasionally stop for a few minutes to improve spacing, the T hopes new vehicles and signal systems will help. So might new technology and procedures to reduce the amount of time trains stop at stations, like adding electric doors on platforms that encourage passengers to stand clear until passengers unload.
Another issue that causes bunching comes toward the start of a trip: the way buses and trains are dispatched.
One big problem with buses, for example, comes when drivers are scheduled to complete trips on one line and then immediately transition to another line. This practice, called interlining, puts pressure on T workers to complete trips on one route so they can move on to the next, leaving little opportunity to adjust for spacing mid-trip. The T is considering ending interlining on busy routes to make them more reliable — it’s already done so on Route 111 in Chelsea — making drivers and dispatchers accountable for spacing, Gonneville said.
“Now we know the dispatchers and transportation managers have the ability to make these adjustments we expect them to make,” Gonneville said.
On the subway side, officials have identified another reason that schedules go out of whack. At some terminal stations, such as Forest Hills on the Orange Line, trains can leave from either side of the platform.
While trains on one side have a straight shot on the inbound tracks and can begin their trips smoothly, those on the other side must snake across the tracks to be on the inbound side, slowing things considerably.
Gonneville said the T is working on new policies and technology that will direct operators on those trains with a slower start to begin trips 20 or 25 seconds earlier than those that run straight away to create more consistent spacing at the start of the runs.
The severity of bunching may depend on your perspective. At a recent public meeting about subway improvements, Transportation Secretary Stephanie Pollack acknowledged that the problem has some benefits.
“It’s nice to get there and watch a train pull out and know there’s one coming two minutes later,” Pollack said. “But it would be nicer if they actually came every five minutes.”
Other riders say they’ve found ways to take advantage of the problem. Taniel Taylor of Revere said she often checks transit tracking apps to plan her trip. When she sees two buses are traveling close together, she deliberately lets the first one pass to get on the second, which she finds to be a far more pleasant ride.
With an app, “you can watch the problem happen,” she said. “I know there’s a million people on the first one, so I purposely go on the other.”