"Generate Service Area" polygon overlaps

[JayJohnsonWashoeCounty]

When I use the Generate Service Area Ready-To-Use tool, I sometimes get weird results.  Even if I've specified "No Overlap", some of the drive time polygons DO overlap, in significantly large areas.  This is particularly troublesome as one polygon can be drawing UNDER another, so it is difficult to tell where these problem areas may be.  

More generally, the boundary between service area polygons from one facility to the next are not "neat" where the two service areas meet - they typically have small overlaps.  This makes using the results a LOT more trouble.

Is anyone else seeing this behavior and are there any recommendations for minimizing/managing this?

[DanPatterson]

What is the coordinate system you are using?  some aren't appropriate

Solved: Service Network Area Polygons are longer than thei... - Esri Community

[JayJohnsonWashoeCounty]

Well, looks like I was caught by the "all our corporate data is in State Plane" assumption.  Mostly true, but for some reason the layer I was using for "Facilities" layer was in GCS_WGS_1984.   Don't know if that was the root of the issue, but I'll re-run the analysis with a Facilities layer in State Plane to see if that helps. 

[JayJohnsonWashoeCounty]

Hmm.  No that wasn't the issue.  With Facilities and Data Frame both in State Plane, here are a couple of screen shots to illustrate the issue:

The two red crosses are the facilities.  The brown polygon is Service Area 1 and the blue diagonal is Service Area 2.  I don't understand why they are on top of each other, when I specified "Not overlapping":

[JaySandhu]

Sometimes there are highways crossing each other with on/off ramps where one facilities service area may go over another one because the lines that make up the service areas did not meet at a place that can be split between two facilities. The polygons are drawn around the lines that are serviced from each facility. 

In the picture you attached, you could also draw the street network and see if that is the case.

Jay Sandhu