Calculate Accessibility Matrix Inconsistent Results

[JosephGarcia]

Hello,

I am having an issue with the Calculate Accessibility Matrix tool from the Transit Network Analysis toolset. I ran this script using a selection of Census Blocks as my origins with a larger set of Census Blocks as my Destinations. I followed the same workflow as shown here: https://www.youtube.com/watch?v=FAmaK1fVpyY which was created by ESRI. Out of the 5,875 Census Blocks ran as origins, 3,784 blocks were given a TotalDest value of 0. Additionally there are many incidences of Census Blocks being located next to each other with one having over 10,000 destinations and the ones surrounding it having 0. With this being a major metropolitan area the results are especially puzzling. Any help or insight would be greatly appreciated. This is my first post on an ESRI forum, apologies if anything was done incorrectly. 

[MelindaMorang]

Hmm, my guess is those remaining problems are some sort of issue in your street data.  The census block centroid has to snap to the closest street feature, and my guess is the street is disconnected from the nearby streets.  You can investigate those street features using the Explore Network tool, and it will show you which adjacent streets and junctions it's actually connected to. This might help you diagnose the problem.  For instance, maybe there is a little gap between the street and the one it's supposed to be connected to.

There could also be some problem with the pedestrian restriction.  Maybe those roads are erroneously restricted to pedestrians.  Explore Network can tell you that as well if you set the travel mode.

[JosephGarcia]

Thank you for that suggestion, it really helped! I'll leave this next part here for any future viewers of this thread.

Using the Explore Network tool I was able to see exactly what was described in the last post, with some roads being erroneously restricted to pedestrians and others being not quite connected to the network. One thing that contributed to the my problem is tied to my use of Open Street Map data for my Streets layer. I found in a number of cases, Open Street Map has line features representing elevated walkways between buildings which fall under the "footpath" highway categorization. These features included skyways between hospital buildings downtown, parking garages to hotels and office buildings etc. These would not necessarily be a problem for this analysis if they weren't the closest feature to the Census Block centroid, and therefore the Street segment the point snapped to. If you are getting weird results in downtown areas and your dataset is derived from OSM data, I would suggest identifying your elevated walkways, they may be the culprit!

Thanks again Melinda for all your help!