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From the user’s perspective, service frequency determines how many times an hour a user has access to the transit mode, assuming that transit service is provided within acceptable walking distance (measured by service coverage) and at the times the user wishes to travel (measured by hours of service). Service frequency also measures the convenience of transit service to choice riders and is one component of overall transit trip time (helping to determine the wait time at a stop).

The service measure used is average headway, which is the inverse of the average frequency. For convenience, Exhibit 3-12 lists LOS by both headway and frequency. Although headways are given as continuous ranges for the purposes of determining LOS, passengers find it easier to understand schedules when clock headways are used (i.e., headways are evenly divisible into 60), particularly when headways are long. When headways are short, clock headways are less important, as customers know that a transit vehicle will arrive soon. Also, delays due to traffic congestion at certain times of the day may require different scheduled travel times for particular trips, in which case clock headways could not be maintained at all timepoints for those trips.

When clock headways are used, vehicles arrive at the same time each hour.

Service frequency LOS is determined by destination from a given transit stop, as several routes may serve a given stop, but not all may serve a particular destination. Some judgment must be applied to bus stops located near timed transfer centers. There is a considerable difference in service from a passenger’s perspective between a bus arriving every 10 minutes and three buses arriving in a row from a nearby transfer center every 30 minutes, even though both scenarios result in six buses per hour serving the stop. In general, buses on separate routes serving the same destination that arrive at a stop within 3 minutes of each other should be counted as one bus for the purposes of determining service frequency LOS.

At some locations, pass-ups may be a regular occurrence, particularly for lower- capacity services unable to accommodate peaks in demand, such as some auto ferries, or transit services following special events. In these situations, some or all passengers must wait longer than the scheduled headway before they reach the head of the line and can board a vehicle. To calculate service frequency LOS in this situation, use an effective headway calculated by multiplying the scheduled headway by the number of transit vehicles that arrive before an average passenger can board. For example, if half the peak hour passengers, on average, must wait for a second vehicle, the effective headway would be 1.5 times the scheduled headway.

Calculating an effective headway accounting for pass-ups.

Exhibit 3-12 Fixed-Route Service Frequency LOS

LOS Avg. Headway (min) veh/h Comments

A <10 >6 Passengers do not need schedules

B 10-14 5-6 Frequent service, passengers consult schedules C 15-20 3-4 Maximum desirable time to wait if bus/train missed D 21-30 2 Service unattractive to choice riders

E 31-60 1 Service available during the hour F >60 <1 Service unattractive to all riders

At LOS “A,” passengers are assured that a transit vehicle will arrive soon after they arrive at a stop. The delay experienced if a vehicle is missed is low. At LOS “B,” service is still relatively frequent, but passengers will consult schedules to minimize their wait time at the transit stop. Service frequencies at LOS “C” still provide a reasonable choice of travel times, but the wait involved if a bus or train is missed becomes long. At LOS “D,” service is only available about twice per hour and requires passengers to adjust their routines to fit the transit service provided. The threshold between LOS “E” and “F” is service once per hour; this corresponds to the typical analysis period and to the minimum service frequency applied when determining hours of service LOS. Service at frequencies greater than 1 hour entails highly creative planning or considerable wasted time on the part of passengers.

Other Measures

Other measures that may be important to consider at the transit stop level include those listed below. Further information about these and other measures can be found in TCRP Report 88(R17) _{and in the references identified with specific measures}

in the following list:

• Pedestrian crossing difficulty can be quantified by crossing delay, using the equations given later in the service coverage LOS section.

• Pedestrian access can be measured by the pedestrian LOS in the vicinity of the stop. For example, the Florida Department of Transportation uses a pedestrian LOS that accounts for traffic volumes, pedestrian facility type, amount of separation between pedestrians and traffic, and other related factors.(R14)

• Bicycle access can be measured by the bicycle LOS in the vicinity of the stop. Researchers(R14,R15) _{have developed LOS measures that account for traffic}

volumes, amount of separation between bicycles and traffic, and other related factors.

• For stops associated with a park-and-ride lot, park-and-ride access can be measured by the lot occupancy (number of parking spaces occupied, divided by the total number of spaces in the lot). At an occupancy of 95% or higher, the lot is effectively full and unable to serve additional potential passengers. • Access for persons with disabilities can be quantified by examining the stop

vicinity (e.g., landing pads, sidewalk widths and condition, grades, curb cuts, etc.) for compliance with the ADA. For example, a stop could be classified as fully, partially, or non-accessible, depending on whether all, most, or only some of the features of the stop vicinity meet the ADA guidelines. ADA access should also consider how frequently ADA-accessible vehicles serve the stop, and—for stations not at-grade—the percentage of time that station elevators are out of service.

• Passenger loading affects availability when passengers are unable to board the first vehicle that arrives, due to overcrowding. The passenger loading LOS measures presented later in this chapter can be used—LOS “F” indicates crush loads where additional passengers would be unlikely to board.