The King Street Pilot has been a success in reducing travel times for streetcars through the core area with knock-on benefits to the outer parts of the route in reduced short turns and more reliable service especially outside of the peak period.
Headway (the space between vehicles measured in time, not distance) is a big issue for riders, and it also affects crowding levels.
If a service is scheduled to show up every 4 minutes, and actually does so, then on average each car will have a similar load (subject to surges that will upset this), and riders can expect an average waiting time of half a headway. Even if they just miss a car, they know fairly certainly that the next one will be along soon, and it might even be in sight.
A chronic problem on all transit services is the bunching of vehicles that can yield two (or more) cars or buses close together followed by a long gap. When cars bunch, riders inevitably pack onto the first one. This is not simply a lemming-like desire to rush the first car, but the effect of years of experience telling riders than when there is a bunch, some of the cars will be short turned. If they are on the first one, they can at least drop back one car when this happens. If they are on the second or third in the parade, they may get dumped off and face the next big gap.
Some transit systems implement time points along a route where vehicles will hold for a scheduled departure time. A more sophisticated version of this is to hold in order to space out service regardless of the schedule. Riders do not care if a car (and its driver) are “on time”, only that the headway is close to the advertised value. It is the transit system’s problem to sort out operator crewing with schedules that can be achieved most of the time, but which are not excessively padded to the point service dawdles along a street. The latter has been a problem on some TTC routes where extra running time overshot the mark leading to annoyingly slow service and congestion at terminals where vehicles arrive early.
With the removal of much of the downtown congestion, and hence the variability in travel times for that part of the route, there was hope that headway reliability would improve. Results to date leave a great deal to be desired. There has been some reduction in the most annoying of wide gaps, but bunching remains a problem.
To be fair, when the scheduled headway is under 4 minutes, some bunching is inevitable. Even if cars leave the termini like clockwork, demands at stops vary as does the traffic enroute, and cars will get slightly off schedule. The follower will catch up, in part because of the lighter load from its shorter headway.
The TTC has a service quality target that all vehicles will leave their termini no more than 1 minute early or up to 5 minutes late. This is the only point on the route where schedule reliability is measured. (Until early 2015, the value was measured at several points along the route to provide a blended score, but this practice was dropped.) There are three basic problems with this scheme:
- A terminus is the simplest place to monitor and dispatch service, and headway variations should always be the lowest at these points.
- When the scheduled headway is small, the allowed 6-minute window for being “on time” permits vehicles to depart in bunches and still be “on time” because they remain within the allowed variation.
- A perfect four minute headway would depart a terminal at 0, 4, 8, 12, 16, 20, 24 … minutes past the hour.
- The same vehicles operating in pairs at 0, 7, 8, 15, 16, 23, 24 … would be “on time” because the alternate cars in the sequence are only three minutes late.
- This problem is worse for wider scheduled headway because until the “five minutes late” line is crossed, the service is on time.
- 0, 6, 12, 18, 24, 30, 36 … and 0, 11, 12, 23, 24, 35, 36 … are both “on time” but the latter actually provides a 12 minute headway of vehicles in pairs.
The TTC has, in effect, constructed a target for “on time performance” that considers bunched service to be acceptable even at a terminal. The problem with this is that as vehicles move along the route, the headway variations get bigger and bigger. It is ironic that even with this generous standard, actual service across the system does not achieve anywhere near the target on the streetcar or bus networks. The streetcar network itself went into a long slide through 2017 thanks to declining vehicle reliability and the proliferation of construction projects.