Waiting for the bus on Robson, Broadway, or 41st, what is important to you: that the bus is “on time”, or that it arrives in the expected frequency interval?
bus operated on schedule
Ensuring scheduled runs, under unreliable traffic condition, can request significant leeway in the layover to absorb any delay at the bus terminus, what can lead to the picture below, which looks like as a poor utilization of bus resource:
buses laying over at Davie and Denman
Furthermore, to respect the schedule along long route, some timing point are necessary to allow adherence to it and to avoid bus bunching.
time point along route 41 (UBC-Joyce Station)
Whether those time points, either
- doesn’t provide enough leeway, and they become useless (the bus is still late on them)
- or provide too much lack- what is not only inefficient, but is frustrating for enroute rider
Normally you could expect that the buses are fairly distributed along the route – to provide a regular interval as built in the schedule, but the reality can be pretty much different:
snapshot of buses on route 41 on thursday Feb 9, 2012, around 2pm
…and bus bunching is still a reality of life:
A zoom on he route 41: 5 east bound bus are spotted here, 3 in the same block, 2 in the 9 others block... Is the bus driver the only one not knowing he is stepping on the back of another bus?
It must be a better way to operate a frequent bus route. When the frequency is supposed to be less than 10mn, do people really care about bus schedule?
bus operated on interval
That is typically, the way the buses in Paris inner city operate: no schedule at all is provided to the customer, just a frequency map. That gives lot of leeway for the operator to operate its bus according to the condition of the day:
- The operator bus schedule can vary according the day of the week, and week of the year
- The operator bus schedule can vary according presence of roadwork, and weather forecast
All that is used by the operator to plan the number of buses to operate on a route at a certain time of a certain day, and is not exposed to the customer, which just care about frequency – and generally understand that bus can’t move faster than traffic (unless bus lanes and other road priorities measure).
To avoid bus bunching, the Parisian RATP operator uses the Global positioning system to inform the bus drivers about spacing with buses in front and behind. The driver is supposed to regulate itself to maintain an optimal interval (so is not asked to adhere to a schedule per sei) 
That makes obsolete the time point mechanism, and eventually is from nature to
- increase the average bus speed
- lower the fleet requirement
The operation on an “interval” is not applied in the Paris suburbs, where bus operates on “schedule” but the operation on “interval” could apriori make sense for high frequency route, like the illustrated route 41…even in Vancouver
 Research result digest, October 1998, Transit Cooperative Research Program