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Esri / public-transit-tools

Tools for working with GTFS public transit data in ArcGIS
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Calculate Travel Time Statistics (OD Cost Matrix) #195

Open yalabbad opened 3 months ago

yalabbad commented 3 months ago

Hi, I have created the network using the GTFS file and street network. I have several questions related to the Calculate Travel Time Statistics (OD Cost Matrix) tool:

  1. Is the output travel time in minutes?
  2. I have tested the tool and set the start time at 7 a.m. and the end time at 9 a.m., and the network data is public transit. In the output table, the mean travel time for some destinations exceeds the time window (2 hours). Why does that happen? Does the travel time include walking time and waiting time?
  3. Also, I have noticed that the tool estimates the time from each origin to each destination, even if the destination is away from the origin.

Thanks a lot

mmorang commented 3 months ago

Thanks for your questions. Happy to help!

  1. Does the output travel time in minutes?

Yes.

  1. I have tested the tool and set the start time at 7 a.m. and the end time at 9 a.m., and the network data is public transit. In the output table, the mean travel time for some destinations exceeds the time window (2 hours). Why does that happen? Does the travel time include walking time and waiting time?

I think you might be confusing two different things. The time window (7am - 9am) is the range of start times for the analysis. The tool calculates the OD Cost Matrix for a start time of 7:00am, 7:01am, 7:02am...8:59am, 9:00am and summarizes the results. The OD Cost Matrix itself just calculates the travel time from each origin to each destination, and it doesn't matter how long that travel time is. the travel time between A and B might be different at different start times depending on the available transit service. That's why the tool calculates the matrix across the time window.

If you haven't seen them already, I think these tutorial videos might help you understand how the tool works. Videos 8 and 12 are the most relevant to this particular question.

Yes, the travel time includes walking, waiting, and riding.

  1. Also, I have noticed that the tool estimates the time from each origin to each destination, even if the destination is away from the origin.

I don't completely understand this question, but the OD Cost Matrix just calculates the travel time from each origin to each destination. This tool doesn't give you the option to use a travel time cutoff because it would mess up the resulting statistics, so it will always calculate the travel time between every origin and every destination, regardless of how far away they are.