Posts about On-time Performance
Transit
Use industry standards for bus and rail on-time performance
WMATA is proposing to lower its targets for on-time performance, because the old targets are arbitrary and they couldn't meet them. How should they pick the right targets that are neither unrealistic nor overly conservative?
Photo by Barbara.K on Flickr.
Monthly, WMATA reports the on-time performance for its buses or trains. Metro considers a bus "on-time" if it arrives at designated time points no more than 2 minutes early or 7 minutes late. We have criticized this in the past, because it can allow frequent buses to bunch while still counting those buses as "on time."
On the rail side, Metro considers a peak period train "on time" if it deviates from schedule by no more than 2 minutes. During middays, evenings and weekends, trains are allowed to deviate from schedule by half of their headway; an train could therefore be 6 minutes off, or 10 minutes off when the trains aren't as frequent, and still be considered "on time."
In this month's report, WMATA proposes reducing the goal for on-time performance from 95% of trains to 90% of trains, and from 80% to 78% for buses.
In response to numerous requests from board members at past meetings, WMATA staff addressed the idea of comparing their on-time performance against other other transit systems. They state in the presentation that comparing performance is not feasible because of differences in operating environments and the data that is reported. Staff also stated that the results can be easily misinterpreted. They concluded that benchmarking against their own performance was the only benchmarking needed.
WMATA could start addressing this incompatibility by standardizing the way it measures on-time performance with how other agencies do it.
The strictest on-time performance metric I could find was used by San Francisco's Muni. They require all vehicles to arrive within one minute early and four minutes late, and by voter mandate are required to meet an 85% on-time performance goal (actual performance is in the mid-70s).
A performance criteria of less than one minute early and less than five minutes late is more typical. The 1 minute early to 5 minutes late or similar criterion is used in Seattle, San Mateo, Oakland, BART, Portland, and Connecticut. Except for CTA, of the transit systems I could find with published on-time performance criteria, Metro's was the worst. Metro's 2 minutes early, 7 minutes late criterion for buses allows more schedule deviation than other transit agencies.
CTA requires reporting rail delays of 10 minutes or greater, and reports raw numbers of incidents rather than percentages, making it impossible to compare CTA to WMATA. However, if Metro were required to report all delays of 10 minutes or greater, that would include a lot of the track fires, offloads and door problems that have become common on the rail system.
My recommendation would be for Metro to use the commonly reported goal for bus of 1 minute early to 5 minutes late, except for buses that are scheduled to arrive more frequently than every 12 minutes, where a headway (time between vehicles) maintenance goal of plus or minus two minutes should be set. As Jarrett Walker described, customers using frequent bus lines do not usually consult schedules, so if every bus on the line is exactly 10 minutes late, it looks the same. Regular spacing is what's important to the customer, not strict schedule adherence.
For rail, Metro should keep the plus or minus two minute headway adherence during rush hours, but during off-peak, establish the same criteria as bus of no more than 1 minute early, and no more than five minutes late. The criteria should not become more generous when there are fewer trains operating.
When trains are operating infrequently, it is usually easier to adhere to schedule because the trains are less likely to interfere with each other. Additionally, infrequent trains make it more important to follow the schedule, since customers are more inconvenienced to miss a train when they come every 20 minutes instead of every 12.
This would establish the same on-time performance criteria for bus as it would for rail. The new criteria would be plus or minus two minutes on headways during rush hours, and one minute early to five minutes late outside of rush hours. At that point, Metro should see what the current performance looks like and set a goal accordingly.
I agree that the operating environment and traffic conditions are different here than in other cities, and the actual on-time performance will vary with conditions. But Metro should at least be informed by how other transit agencies measure and report the data, and adjust their metrics so some comparison can be made.
Transit
Bus on-time performance: It matters what you measure
Every month, Metro's customer service committee looks at a presentation on operating statistics, including a chart showing the latest bus "on-time performance" percentage. That percentage reflects the number of buses that arrive within a certain time before or after the published schedule
Photo by aussiegall.
If the on-time percentage improves or degrades, without looking any further, could Metro say why? If the percentage degrades drastically, could the Board do anything other than ask management to do a better job? Management needs to be able to identify trends, detect problems with individual routes or trips, and focus their attention on the areas that might need more resources or oversight.
The single on-time performance percentage also does not identify problems with bus bunching, especially on frequent routes. Imagine a bus line that is supposed to have service every ten minutes, but experiences bunching. Take five buses in a row starting at 8am (see top line in the figure), bunch the middle three together and spread the other two out (see bottom line in the figure). This is a worst case, but under Metro's on-time percentage rules, all of these buses are considered "on-time," because each bus is no more than two minutes ahead of or seven minutes behind schedule.
The green bar shows the range of times the 8:20 bus could arrive and still be considered on-time. A passenger arriving just on time for the 8 am bus will have just missed it, as it left two minutes early, and will have to wait until 8:17 for the next bus. That's a wait of just over seventeen minutes for a bus that's supposed to come every ten!
London looks at bus on-time measuring differently. Because the bus lines in London are operated by private contractors, it's very important for the local transit authorities to accurately measure on-time performance because there are real financial incentives or penalties involved. They measure how often buses pass by certain points on the network and track the "excess waiting time." All that time you have to wait for a bus that's running late or is bunched with others is added up and averaged over the route, and the excess waiting is compared to how much you'd normally have to wait assuming you come to the bus stop randomly. The reports for bus performance are published on the web.
In our example above, the average scheduled wait time is five minutes, and there are two buses you'd have to wait on average eight minutes, so the excess waiting is six minutes total, about 1.5 minutes per bus, or about 30% extra. (Under the London system, buses don't get credit for making you wait less than average.) This makes it easy to see when high-frequency buses are not meeting the required headways, and London applies this calculation to all buses that are supposed to come every 12 minutes or better. They even post the information on the web quarterly.
Metro should adopt London's system to measure on-time performance. The current measurement does not work for frequent buses. The London model focuses on the rider experience, compares various bus routes' performance, and gives a sense of the magnitude of the problem. In addition to this change for high-frequency bus routes, Metro should start regularly reporting on-time performance figures for all bus routes, as part of the monthly ridership report. They should also highlight the worst performing lines for each jurisdiction. If the problem is somehow Metro's fault, the route can receive the appropriate management attention. More likely, traffic congestion or other factors are at fault. In that case, data in hand, Metro Board members could make their case with state and local transportation officials to make transit operation a higher priority on corridors that are experiencing poor performance.
By identifying and improving poor performing bus lines, we can get people moving to their destinations more quickly, and reduce operating costs. Faster travel speeds and more regular schedules would drive up ridership, improving Metro's bottom line and allowing more service with the same local subsidy. Metro should revise the way they present performance metrics to make it possible.
@ggwash
- Successful speed cameras require fair speed limits
- Amid scandal, don't lose sight of Gray's policy achievements
- Bethesda gets new but terrible bike racks
- Montgomery plans 160-mile, "gold standard" BRT system
- DC's parks are 5th best in the nation, says "Park Score"
- DC's divide need not be black and white
- Live chat with Matt Yglesias
Greater Washington
District of Columbia
