Avoiding bunching and gapping: easier said than done

In the last few years, expanding high-frequency transit service has become a hot topic at transit agencies across the country, and for good reason: research shows that frequent service is one of the best ways to keep riders of public transit, well, riding public transit.

But that’s about as far as the consensus goes, with many agencies struggling to put high-frequency plans into action. Headway management, in particular, is one of the toughest obstacles to overcome when it comes to keeping vehicles evenly spaced, causing well-thought-out plans to break down in practice.

That’s why we caught up with the team at Capital Metro in Austin, TX, in a recent webinar to understand how their latest headway management pilot guided their long-term plan for high-frequency corridors. In their six-month pilot on Austin’s MetroRapid BRT line, the Capital Metro team uncovered best practices around dynamic and proactive headway management that can help any agency that’s strategizing on high-frequency service.

Here’s what they learned:

1. Agencies need a consistent method of measuring and analyzing bunching and gapping

As the saying goes, what isn’t measured cannot be managed, and high-frequency transit service is no exception. And unlike on-time performance metrics, which compare vehicle arrivals against a static schedule, headway metrics require some data gymnastics to get it right.

“The biggest quirk with measuring actual headways is that success is a moving target,” says Dottie Watkins, VP of Bus and Paratransit Service at Capital Metro. “That means measuring your operations will be much more dynamic than normal schedule-oriented routes.”

At Capital Metro, the operations team uses GPS data to capture when a given vehicle arrives at a stop, then counts how long it takes for the next vehicle to arrive, comparing that observed headway with scheduled headway. If what they capture is within a range of 50% to 150% of the scheduled headway, they call it on time. If it’s below that range, it’s bunched; above that range, gapped. Capital Metro also recently began using Swiftly to analyze this data using the Headway Insights module.

“Keeping vehicles spaced evenly on high-frequency routes is sort of like fighting forest fires,” Watkins says. “We don’t want to just wait around for fires to happen. We want to get ahead of them and start fighting them before they begin.”

2. Dispatch alone can’t eliminate bunching and gapping

If the pilot at Capital Metro taught the operations team one thing, it’s that dispatch alone only goes so far. A major tactic of the pilot was ensuring vehicles strictly adhered to departure times at the beginning of trips to help even out vehicle spacing down the line. The effects weren’t as impactful as they’d expected.

“For two weeks, we made sure that vehicles left the terminal every ten minutes, down to the second,” explains Kirk Hovenkotter, transit advocate who designed and analysed the Capital Metro project. “It definitely helped, but after about three or four miles, things started to break down in a major way.”

For one, the human element was hard to control for. The Capital Metro team uncovered that bus operators, who had been trained for years to keep to a schedule, found it difficult to change their mindset to one where schedules don’t really matter. “It took longer than expected to train them on a such a structural shift in their thinking,” Watkins says.

But more than anything, traffic was the fundamental issue. During the pilot, vehicle run-times changed dynamically and randomly with traffic, making it hard to run reliable headways without constantly starting and stopping vehicles. “It’s hard to keep things consistent without putting so much slack into the schedule that you’re wasting time and money,” Watkins adds. “That’s when we knew we had to get other city stakeholders involved.”

3. Transit signal priority and devoted bus lanes are key for consistent headways

Ebbs and flows in traffic patterns can make it difficult for agencies to proactively manage vehicle spacing, but small capital projects can go a long way in getting around these types of externalities.

Since launching the MetroRapid line in 2014, Capital Metro has successfully lobbied for transit signal priority (TSP) projects to minimize the variable run-times due to traffic congestion. And metrics were the secret ingredient in convincing other city stakeholders that it was worthwhile.

“We used the headway numbers we collected with our GPS units to approach the City of Austin to get more aggressive TSP implemented at certain intersections,” Watkins says. “And strong metrics have also helped us brainstorm other options, like a ‘contraflow’ system where light signals allow buses to go the wrong way down a one-way street to get around the most congested areas. But without a solid foundation of metrics, we would’ve had a much harder time getting any of this through.”

4. Data is an operations team’s best friend

If it takes a village to keep high-frequency transit from bunching and gapping, data is the language they speak in the village. Data brings decisions back to what matters most.

“Different departments and orgs all have their priorities, but at the end of the day, it’s our citizens we want to help,” Watkins says. “Good data allows us to tell other stakeholders that we’ve tried many things but that we still need their help to go even farther to help our city function efficiently. And so far, it’s gone a long way in convincing them.”

Reliable trips = improved ridership

There may not be a simple solution to headway management, but frequent, reliable transit service has helped to slow the downward trend in ridership, so reliability should be bolded, capitalized, and underlined in every operations team’s playbook.

“One of the most important factors in a person’s decision to take transit is a reliable trip,” Hovenkotter says. “Riders want to know they can budget the same amount of time at Monday at 10am and on Tuesday at 10am. The more variation there is, the harder it is to schedule around travel times, and people stop taking the bus.”

“But the opposite is true too,” he adds. “The more consistent and reliable transit service is, the more people will trust public transit as a dependable way of getting from A to B.”

In case you missed the webinar, you can watch the full discussion here:

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