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MTA's Half Minute Concept

Posted by BusRider on Sun May 21 22:23:37 2017

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Going through the GTFS data, a lot of trips have :30 seconds added, commonly for Holds, but in other areas as well.

Are these times rounded at all, especially when calculating running time? Some trips have the :30 and others don't.

For example, some trips on the Weekday #2.

Flatbush to 241 8:57:30 to 9:23:00

Flatbush to 241 14:01:30 to 15:40:30

Now would it be 8:58-9:23 and 14:02-15:41 or 8:57 to 9:23 and 14:01 to 15:40?

Any assistance is appreciated.

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Re: MTA's Half Minute Concept

Posted by SLRT on Mon May 22 08:11:31 2017, in response to MTA's Half Minute Concept, posted by BusRider on Sun May 21 22:23:37 2017.

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Even on the old printed ETTs, there were 1/2 minute timings, especially on lines with tight headways, like Flushing.

30 seconds is actually a long time. I think the issue is less pinpoint accuracy than avoiding the distortions that rounding could create.

After all, the Dual Contracts called for 90 second headways, in an Era of much shorter trains.

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Re: MTA's Half Minute Concept

Posted by Fine, Howard, and Fine on Mon May 22 09:47:20 2017, in response to MTA's Half Minute Concept, posted by BusRider on Sun May 21 22:23:37 2017.

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Half minute precision in planning is important especially for managing merges and express/nonexpress interleaves.

A line might have a round number of minute headways for both rush and midday, but when ramping service level down after morning rush, or before evening rush, it's very handy to step through fractionAl minute headways along the way.

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Re: MTA's Half Minute Concept

Posted by Stephen Bauman on Mon May 22 12:48:35 2017, in response to MTA's Half Minute Concept, posted by BusRider on Sun May 21 22:23:37 2017.

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Can you be a bit more specific? Which GTFS data are you using and what's its date? The latest available static GTFS schedule (release date not creation date) is dated Jan. 30, 2017.

It shows no #2 train scheduled to depart from Flatbush at 8:57:30. It does show a #2 trains scheduled to depart at 14:01?:30. However, no 30 second hold times are shown at any intermediate station. (The hold time is defined as the interval between scheduled departure and schedule arrival).

There is however a scheduled hold of 5 minutes at 238th St. The MTA's on time performance (OTP) metric is defined as a train being arriving at its terminal more than 5 minutes after its scheduled arrival. The scheduled 5 minute hold makes the OTP statistic look good.

The scheduled train id is: A20161106WKD_084150_2..N01R. This can be interpreted as follows:

A - division A (IRT)
20161106 - date that the schedule was created (6 Nov 2016)
WKD - weekday
084150 - scheduled departure in hundredths of minutes
2 - route id
N01R - route description (corresponds to route id in shape file)


Here's its schedule, that you can cut and paste into a spreadsheet.

"stop sequence";"stop name";"arrival";"departure";"hold"
1;"Flatbush Av - Brooklyn College";"14:01:30";"14:01:30";"00:00:00"
2;"Newkirk Av";"14:03:30";"14:03:30";"00:00:00"
3;"Beverly Rd";"14:04:30";"14:04:30";"00:00:00"
4;"Church Av";"14:06:00";"14:06:00";"00:00:00"
5;"Winthrop St";"14:07:30";"14:07:30";"00:00:00"
6;"Sterling St";"14:09:00";"14:09:00";"00:00:00"
7;"President St";"14:10:30";"14:10:30";"00:00:00"
8;"Franklin Av";"14:13:00";"14:13:00";"00:00:00"
9;"Eastern Pkwy - Brooklyn Museum";"14:15:00";"14:15:00";"00:00:00"
10;"Grand Army Plaza";"14:16:30";"14:16:30";"00:00:00"
11;"Bergen St";"14:18:30";"14:18:30";"00:00:00"
12;"Atlantic Av - Barclays Ctr";"14:20:00";"14:20:00";"00:00:00"
13;"Nevins St";"14:21:30";"14:21:30";"00:00:00"
14;"Hoyt St";"14:23:00";"14:23:00";"00:00:00"
15;"Borough Hall";"14:24:30";"14:24:30";"00:00:00"
16;"Clark St";"14:26:30";"14:26:30";"00:00:00"
17;"Wall St";"14:30:00";"14:30:00";"00:00:00"
18;"Fulton St";"14:31:30";"14:31:30";"00:00:00"
19;"Park Pl";"14:33:30";"14:33:30";"00:00:00"
20;"Chambers St";"14:35:00";"14:35:00";"00:00:00"
21;"14 St";"14:39:30";"14:39:30";"00:00:00"
22;"34 St - Penn Station";"14:42:00";"14:42:00";"00:00:00"
23;"Times Sq - 42 St";"14:43:00";"14:43:00";"00:00:00"
24;"72 St";"14:47:00";"14:47:00";"00:00:00"
25;"96 St";"14:50:00";"14:50:00";"00:00:00"
26;"Central Park North (110 St)";"14:54:30";"14:54:30";"00:00:00"
27;"116 St";"14:55:30";"14:55:30";"00:00:00"
28;"125 St";"14:57:00";"14:57:00";"00:00:00"
29;"135 St";"14:59:00";"14:59:00";"00:00:00"
30;"149 St - Grand Concourse";"15:02:30";"15:02:30";"00:00:00"
31;"3 Av - 149 St";"15:04:30";"15:04:30";"00:00:00"
32;"Jackson Av";"15:07:00";"15:07:00";"00:00:00"
33;"Prospect Av";"15:08:30";"15:08:30";"00:00:00"
34;"Intervale Av";"15:09:30";"15:09:30";"00:00:00"
35;"Simpson St";"15:10:30";"15:10:30";"00:00:00"
36;"Freeman St";"15:12:30";"15:12:30";"00:00:00"
37;"174 St";"15:14:30";"15:14:30";"00:00:00"
38;"West Farms Sq - E Tremont Av";"15:16:30";"15:16:30";"00:00:00"
39;"E 180 St";"15:18:00";"15:18:00";"00:00:00"
40;"Bronx Park East";"15:20:00";"15:20:00";"00:00:00"
41;"Pelham Pkwy";"15:22:30";"15:22:30";"00:00:00"
42;"Allerton Av";"15:24:30";"15:24:30";"00:00:00"
43;"Burke Av";"15:26:00";"15:26:00";"00:00:00"
44;"Gun Hill Rd";"15:27:30";"15:27:30";"00:00:00"
45;"219 St";"15:29:30";"15:29:30";"00:00:00"
46;"225 St";"15:30:30";"15:30:30";"00:00:00"
47;"233 St";"15:32:00";"15:32:00";"00:00:00"
48;"Nereid Av";"15:33:30";"15:38:30";"00:05:00"
49;"Wakefield - 241 St";"15:40:30";"15:40:30";"00:00:00"

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Re: MTA's Half Minute Concept

Posted by Stephen Bauman on Mon May 22 13:00:25 2017, in response to Re: MTA's Half Minute Concept, posted by Fine, Howard, and Fine on Mon May 22 09:47:20 2017.

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Half minute precision in planning is important especially for managing merges and express/nonexpress interleaves.

It's utterly inadequate. It takes approximately 1 minute (60 seconds) for a train to enter and clear an interlocking. Suppose trains are scheduled to arrive at the merge every 2 minutes (30 tph). If leader and follower are within 30 seconds of their scheduled arrival, then the follower will not be delayed. Leader and follower must be within 15 seconds of schedule, to guarantee no delays for 90 second headways(40 tph).

Clearly, keeping track of schedules to a 30 second precision is as useful as using a sundial in the subway. Systems that operate around 40 tph, measure station arrival/departure times in seconds. Their crews are expected to maintain such schedules because there is a departure clock at each station that measures time in seconds.

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Re: MTA's Half Minute Concept

Posted by randyo on Mon May 22 13:07:14 2017, in response to Re: MTA's Half Minute Concept, posted by Stephen Bauman on Mon May 22 13:00:25 2017.

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The half minutes don’t exist on their own but only in combination with a full integer. It has been SOP in the schedule dept that the minimum interval between trains is 1 1/2 min and intervals that close are only used when absolutely necessary for trains to clear multiple lines where a full 2 min would impact on one or another of the lines that a particular train would have to clear.

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Re: MTA's Half Minute Concept

Posted by BusRider on Mon May 22 13:28:08 2017, in response to Re: MTA's Half Minute Concept, posted by Stephen Bauman on Mon May 22 12:48:35 2017.

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I'm using the Jan 30, 2017 file.

The two trips are:

From 241st to Flatbush
7:47:30 departure with 9:31:00 arrival and

From Flatbush to 241
10:26:30 departure with a 12:05:30 arrival

All I am trying to do is calculate the running time.

When you look at the these trips on a public timetable the numbers are rounded so:

a 7:48 -> 9:31 and 10:27 -> 12:06 respectively.

I keep getting confused, are you supposed to round all the times?

Or would it be 7:47/9:31 and 10:26/12:05?

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Re: MTA's Half Minute Concept

Posted by italianstallion on Mon May 22 18:17:02 2017, in response to Re: MTA's Half Minute Concept, posted by BusRider on Mon May 22 13:28:08 2017.

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So the public table rounds to a later time? So someone getting there at 10:26:45 for the supposed "10:27" departure would miss it.

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Re: MTA's Half Minute Concept

Posted by BusRider on Tue May 23 11:31:09 2017, in response to Re: MTA's Half Minute Concept, posted by italianstallion on Mon May 22 18:17:02 2017.

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Correct on your first statement. You can also notice it in the Trip Planner on the MTA website.

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Re: MTA's Half Minute Concept

Posted by randyo on Tue May 23 14:50:32 2017, in response to Re: MTA's Half Minute Concept, posted by italianstallion on Mon May 22 18:17:02 2017.

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The public timetable should actually round off to the earlier time so that passengers cutting their travel time close would not miss the train (LOL). Years ago, I recall seeing signs posted at certain stations which actually listed the departure times of every special rush hour service train during their hours of operation, and many of these displayed departure times that included half minutes.

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