“The Unreliables”

Fall 2006

METHODOLOGY

Bus routes were put on the list of “The Unreliables” if more then one out of five of its buses arrived in bunches or with big gaps in service, or departed significantly off schedule, according to MTA New York City Transit’s own statistics for the first half of 2006.

In the judgment of the Straphangers Campaign and Transportation Alternatives, buses should not have a rate of irregularity of more than 20%. Most bus riders would agree it is a poor level of service to have more than one in five buses arrive significantly off their scheduled interval during the day or at any time point at night.

In this methodology, we explain how we used MTA New York City Transit’s official statistics to rate the reliability of bus service.

Wait Assessment
MTA New York City Transit reports two “indicators that measure service performance from a customer-oriented perspective” on a semi-annual basis.

The first is “wait assessment.” It is used during the day — from 7 a.m. to 7 p.m. Under New York City Transit’s standard, a bus has an acceptable wait if it arrives within three minutes of its scheduled interval during the “peak” period, 7 a.m. ­ 9 a.m. and 4 p.m. ­ 7 p.m.

The standard for the “off-peak” period (9 a.m. ­ 4 p.m.) is an arrival within five minutes of a scheduled interval.

New York City Transit defines “wait assessment” as the percentage of service intervals no greater than the scheduled interval plus “either three minutes during the peak or five minutes during the off-peak.”

As an example, the B44 bus along Nostrand Avenue to Emmons Avenue is supposed to come every nine minutes during the off-peak period around noon. Its arrival is rated as acceptable by transit officials if two B44 buses arrive between six minutes and 14 minutes apart from one another. If a B44 bus arrives 20 minutes after the previous one, it would get a negative wait assessment rating.

Schedule Adherence/En-route On-Time Performance
The second official indicator is “Schedule Adherence/En-route On-Time Performance.”

It is defined as “the percentage of trips departing from all scheduled en-route time points between one minute before and five minutes after scheduled departing time.” It is assessed at night — from 7 p.m. to 7 a.m. — “when service is less frequent and customers are more likely to rely on schedules.”

As an example, let’s use the B44 again and say it’s scheduled to come to a time-point location at 10:09 a.m., 10:18 a.m., 10:27 a.m., 10:36 a.m., 10:45 a.m. and 10:54 a.m. It would be rated as off schedule at that time point location if it departed at 10:07 p.m. (two minutes early) or at 10:24 p.m. (six minutes late).

Weighting the Two Indicators
Approximately 85% of New York City bus riders use the system during peak-hours; 15% use them during the off-peak, according to MTA New York City Transit.

Therefore, we weighted New York City’s two indicators for bus service. Let’s take the calculations for the B44 as an example.

New York City Transit gave the B44 a “wait assessment” rating of 79.7% for the first half of 2006, the most recent period available. That meant that 20.3% of buses on the route did not meet wait assessment standards. Therefore more than one out of five buses were rated to be outside the scheduled interval during the day.

It also rated 38.1% of the B44 as not adhering to schedule at night.

We multiplied the wait assessment by 85% yielding a result of 17.26 (20.3% x .85 = 17.26.)

Then we multiplied schedule adherence by 15% yielding a result of 5.72 (38.1% x .15 = 5.72.)

We then added the two numbers together — 17.26 + 5.72 — which equals 22.98%. We rounded the final number to the nearest tenth, yielding an overall unreliability rating of 23.0%. This means that 23% of the buses on the B44 arrived in bunches or with major gaps in service, or departed significantly off schedule, according to MTA New York City Transit’s own statistics for the first half of 2006.

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