Transit
A Timetable Is Built Backwards From The Crew Roster
Published departure times are constrained by shift lengths, break rules and where staff start and finish, which explains gaps in service that no passenger demand accounts for.
A timetable looks like a response to demand. A large part of its shape comes from the rules governing how long staff can work and where they must begin and end.
Duties have to close as well as open
A driver's shift starts and finishes at a location with facilities, and the sequence of journeys in between must return them there within the permitted hours.
Building a duty is therefore a matching problem, linking trips into chains that begin and end in the right places at the right times.
Trips that cannot be linked into a workable duty are difficult to run at all, however useful they would be to passengers.
Break rules create structural gaps
Regulations require breaks of defined length after defined periods of driving, and those breaks must be taken somewhere with facilities.
Scheduling a break means the vehicle is either standing idle or handed to another driver, and the second option needs a relief point and someone available there.
Where relief is impractical, the break appears in the timetable as a longer gap than demand would justify, usually in the middle of the day.
Peak requirement sets the establishment
The number of drivers employed is determined by the busiest period, since every vehicle in service at the peak needs someone in the cab.
Those staff are paid for a full shift, which means labour is available outside the peak whether or not it is used.
This is why marginal off-peak service is cheaper than it appears, and why cutting it saves less than the timetable reduction suggests.
Vehicle and crew schedules interact
A vehicle can run continuously while drivers change, so the fleet requirement and the staff requirement are solved as related but separate problems.
Optimising one worsens the other, and the software used to build schedules trades between them according to relative cost.
Because staff cost more than vehicles in most operations, the crew schedule usually wins, and the vehicle diagram absorbs the inefficiency.
The first and last services are the hardest
An early departure requires a driver to start before it, which means transport to the depot at a time when nothing else is running.
A late service ends with a vehicle and a driver away from base, both of which must be returned without carrying passengers.
These dead runs cost as much as revenue service, which is why the span of a timetable contracts faster than its frequency when budgets fall.
Questions readers ask
Do bus lanes make congestion worse for other traffic?
They reduce general traffic capacity on the link, and effects vary with how much traffic shifts to the bus. Corridors have generally adapted more than fixed-demand models predicted.
What is conditional signal priority?
Priority granted only when a bus is behind schedule or above a certain occupancy, rather than to every bus. It targets the delay that matters while limiting the impact on other movements.
