I'm using the Network Analyst extension in ArcMap 10.2 to calculate the shortest routes between ~50000 pairs of stops. I've set the impedance to "Length (Meters)" and the resulting Routes Featureclass has a field for "Total_Length" and "Shape_Length". However, 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.
Another thing which I noticed, which may or may not be related to this, is that the routes simplify the network edges. When I zoom into routes along round network edges, it appears that the calculated route does not match the edge, but instead is a straight line between the vertices of the edge. The offset from the true edge is very small (~0.002m), but it is causing me problems with further intersect analyses.