I am trying to develop isochrones (polygons showing how far you can get from a bus stop in a certain amount of time) for an entire transit network. In order to do this, I have created a custom network dataset that incorporates the transit system's GTFS and the pedestrian network using the Add GTFS to network dataset toolbox.
I have managed to develop accurate travel distances using my custom network datasets and the toolbox, but now I am hitting a snag with the automatically developed polygons.
Simply solving a Service Area in Network Analyst doesn't capture how far you can get at ANY time, so to get around this, I used the Prepare Time Lapse Polygons tool to show how far you can get in 15 minutes by transit at any time between 8 and 8:30am then dissolved all polygons with the same Facility ID. Unfortunately, the polygons do not account for barriers that would prevent a person from actually reaching a location in 15 minutes, ie. Highways.
The image shows an example of this issue. The green point is one bus stop that is located very close to a highway, shown as the red line. The pink polygon is the area that was developed by the time lapse polygons tool. The area outlined by the black dashed line is not actually accessible within 15 minutes because of the physical barrier of the highway. However, the polygon is showing it as accessible within 15 minutes.
I have attempted incorporating a network restriction in the Service Area prior to running the Time Lapse polygons tool, but this only prevents the lines generated from the Service Area from crossing the highway barrier.
My question is, is there a way to automatically prevent the polygons from showing these inaccessible areas as accessible, eg. cut out the area outlined in black dashes, and for any similar locations? Otherwise I will have to cut several hundred polygons manually.