Principle 3: Reliability

The degree of dependability of the frequent network core relies heavily on service reliability: predictable travel times and regular stop departures. Similar principles apply for infrequent routes as well, in which punctuality is defined as adherence to scheduled stop departures.

Vehicle travel time buffers that are built into bus schedules are crucial to ensure reliability. Proper stop spacing and route streamlining also help to increase route service efficiency. Real-time information may help only up to certain extent, as multiple-leg trips, which depend on frequent network synergy, still require every single route service to not to deviate from its schedule.

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Stop spacing and journey predictability affects travel time

Stop spacing

Stop spacing differs by service length and purpose, as people will walk farther to access faster and more reliable services.

A rapid transit (MRT, LRT, BRT) service that runs every 5-mins or less on dedicated and separated right-of-way attracts 800m walk, and thus stations are best spaced 1.2-1.5km apart.

Walking radius and stop spacing are reduced to 600m and 750m-1.2km respectively for surface trams or limited-stop buses on dedicated but not separated right-of-way.

A bus or tram service that runs frequently on mixed traffic (with some priority measures) attracts 400m walk, and thus stops are best spaced 400-750m apart.

A local service that runs infrequently on mixed traffic attracts 200m walk, and thus stops are best spaced 300-500m apart.

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Walking coverage depends on service characteristics


Bus scheduling basics

Reliability for less frequent bus services is measured by punctuality along the route: the closer the buses arrive to scheduled timing, the more reliable the service. Punctuality along a route cannot be objectively measured without scheduled timepoints.

A timepoint is a public transport stop that a vehicle tries to reach at a scheduled time; a vehicle is not supposed to pass a timepoint until the schedule time has arrived. Typically, a predictable service offers information on arrival times at selected timepoints, which are well-spaced throughout the entire service route. As travel time changes, it is normal for transit agencies to readjust schedules when needed. Analytics of historical vehicle tracking datasets will lead to more accurate timepoint-based scheduling, and more realistic targets to be imposed in performance contracts for operators.

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Reliability for frequent bus services is measured by regularity of headway: the more evenly-spaced bus intervals are, the more reliable the service. Reliability indicators such as EWT (Excess Wait Times) are useful in identifying mitigation measures to improve frequent bus services’ regularity performance, and measuring effectiveness of the implemented measures.

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Bus stop basics

The most fundamental design aspect of a bus stop is that it must allow the bus to safely pull over to the pedestrian curb to ensure its front entrance aligns with the bus stop pole or signage where passengers are expected to line up.

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A typical North American curbside bus stop (Canada’s Toronto Transit Commission)

A bus stop, especially the ones that serve frequent buses, must not be blocked by any other non-emergency traffic vehicles in any circumstances. Bus bays, which may be required at selected bus stops for drivers to abide by the scheduled timepoint buffers, must be designed to ensure obstruction-free entry and egress, such as Singapore’s mandatory give-way-to-bus law that penalises hefty fines to errant motorists. If possible, bus boarders should be preferred over bus bays as the former allow buses to merge back into traffic without delay. Special attention should be also given with respect to conflict points with other modes such as bicycles.

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No-standing-at-bus-stop sign in Vancouver, mandatory give way to bus marking and bus boarder in Singapore, and bus float in the UK (Vancouver’s Georgia Sraight, Singapore’s Today Online, PushBikes.org.uk)

Specialised curb design, such as Kassel Kerb, allows minimal clearance gap for entering and disembarking passengers, which is crucial to reduce dwell times and increase reliability.

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Reliability enhancement measures

Travel time predictability is a concern for high frequency buses operating in mixed traffic with highly unpredictable congestion, as transit schedulers are left with no choice but to allocate excessive travel time buffers to avoid bus bunching. As traffic worsen over time, this stretches the amount of service hours to be covered by each vehicle, resulting in watered-down frequency.

Rather than relying on timepoint-based time buffers alone, there are several reliability enhancement priority measures that can prevent frequent buses from bunching and improve vehicle travel times, passenger boarding and exit times, and passenger connection delays.

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Examples of reliability measures to cut travel times (images from various google search sources)

Permanent bus priority infrastructure, such as bus lanes, queue jumps, and traffic signal priority, are the best solution to cut both dwell times and travel times while simultaneously increase service productivity.

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Unpredictable travel times and dwell times are the core challenges for any frequent bus service

As bus priority infrastructure may not be realistically applicable to the entire bus route stretch due to fiscal and implementation constraints, a combination of measures may be used to reduce travel times unpredictability and passenger flow issues.

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Variety of measures that can be synchronously introduced to increase reliability of frequent buses (images from various google search sources)