If your route has been calibrated (meaning it has M values), you can use a simple piece of code in field calculator to get the minimum and maximum M values for each line segment. Create a double type field for the begin value and the end value. Enter the calculate field dialog box for the fields, choose the Python parser (instead of VBScript), and input the following:For Begin Value: !shape.extent.mmin!For End Value: !shape.extent.mmax!I hope this helps!