Fixed-route scheduling

From TransitWiki
Revision as of 05:17, 27 November 2013 by Jlarose (talk | contribs)
Jump to: navigation, search

THIS ARTICLE IS UNDER CONSTRUCTION

Introduction

Agencies operating fixed-route buses find the need to make adjustments to route scheduling periodically in response to changing circumstances. Bus transit planners should be aware of the basics of fixed-route scheduling. This topic does not cover development of a new fixed-route service, but rather the tuning or re-tuning of an existing or already planned route.

Different agencies value different qualities in service levels. The minimum or average frequency of service may be set by agency policy. Alternatively, some agencies may focus more on geographic coverage over frequency. Achieving success in both aspects is unlikely due to the high cost of having high frequency and extensive coverage. Priorities can extend further into how aggressive the bus schedule is against traffic congestion, or how relaxed it is by allowing more layover or recovery time along the route.

Basics

The characteristics of the area will often determine the basic components of service. How frequently will the route run? Where will the bus stops be and what is the distance between them? In small communities, suburban and rural, service may operate once an hour; in major metropolitan areas services may run every ten minutes or even more frequently. Certainly there is a wide range in between. In areas where a route operates on frequent headways, say every 10 minutes or less, passengers more often walk out to the stop without knowing the departure schedule; at most they are likely to only be waiting an average of 5 to 9 minutes for the next bus. When service is less frequent than about every 10 minutes, passengers will have to rely more heavily on the published schedule. In these cases it becomes even more critical that the route timetable is appropriate for operating conditions such as traffic levels at different times of day.

While some agencies may calculate average time between every stop, it is more common for agencies to designate scheduled "time points" along a route. A time point would be a major stop by which the driver knows they cannot pass earlier than what is published. The precise time for stops in between is unpublished. Passengers read the schedule and if they are waiting at a stop in between can reasonably estimate when the bus will come based on the time points on either side of their stop. This can simplify published information and also allow flexibility on stretches of the route with a high variability of speed.

To establish a basic schedule, it is best to set time points that are evenly spaced along the duration of the route. A reasonable guideline would be a time point every five to ten minutes apart. Agencies often set time points using major and recognizable landmarks or intersections. Calculate the average free-flow (no traffic delay) time between each time point.

Putting it all together

Adding up times between timepoints. Be sure to allow time for boarding, hopefully based on real or projected ridership. Estimate delay if needed, use an agency average, etc. Add recovery or layover time. Good rule of thumb is 10% of round-trip time. Lay out route in a table with departures based on target frequency.

Usually good to test draft product to watch for hiccups.

Some revision may be needed. Small amounts of slack time in the middle of a route may be necessary to account for travel variations. If planning flexible transit route, need to incorporate slack time for deviations but not so much that a no-deviation trip isn't sitting around waiting exceptionally long times.

Agency Variation

The type of agency and minimum service level vary tremendously between very large cities and small urban areas. Small urban areas may only support hourly or 30-minute headways where in a large city the maximum headway may be 10 minutes or less.

Agencies working with long headways and multiple routes need to carefully consider connections and probably allow greater slack time.

Adjusting factors

Sometimes once everything is factored in, a route appears inefficient. For example, a route in free-flow can do a round trip in 40 minutes, but when all other factors are added the run time is 65 minutes. It may be desirable to get the route down to 60 minutes or less.

Examine: passenger stop delay (boarding, alighting), average traffic speed, signal delay, geographic factors - are buses slowly crawling through tight areas that could be avoided, etc. Use various strategies to reduce. Avoid making route so tight only the best/senior operators are capable of handling it safely. Keep operations administration involved.

Runcutting and operations

SEPARATE ARTICLE? Once a route is scheduled (or rescheduled), service needs to be segmented into blocks of work.

Factors

Federal, state, and agency labor policy. How many hours can employees work, how is work assigned (seniority, etc.)