Why does the shortest route calculation in ArcMap show a longer alternative?

02-04-2021 01:54 AM
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I have been conducting shortest route (SR) analysis in ArcMap. I had a school (a facility/start point) and many students who go to this school by walking. I asked students to draw their route to go to school. I wanted to see the difference between their actual route (the drawn route) and their shortest routes.
In Arcmap:
1) I used "new closest facility" option in network analyst. 
2) Each school was described as a "facility" and all students who go to that school were defined as "incidents". 
3)Then I opened properties/analysis settings/impedance, I selected "length" option and properties/accumulation, I selected "length" again. So it would be based on distance
4) And then I solve the network and routes were automatically created. 
Th calculation was succesful for some of the students. However, the shortest route was longer than the actual route for some of the students. Please see the example attached. Here, the actual route was highlighted with purple and the shortest route is the blue line.
5)Then, I thought I can just select one school-one home (rather than analysing all houses together) and this time I can use  "new route" option and conduct the same analysis. The result was the same. And still, shortest route was longer than the actual one.
Can someone let me know the problem here? 
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