I'm using the Network Analyst extension in ArcMap 10.2 to calculate the shortest routes between ~50000 pairs of stops. As the impedance is set to "Length (Meters)" the resulting Routes Featureclass has a field for "Total_Length" and "Shape_Length". What is confusing me, is that the values in these two fields are not the same, they differ by +15m to -0.5m. At first I assumed that this had something to do with the distance of the stops to the network, but looking more closely at some of the routes, the distance to the network doesn't match the difference in length. I've also re-run my analysis with a 0m offset of the Stops from the network, but the length differences stayed the same.
Has anybody else come across this before or does anybody have an idea of why this is happening?