A route identifier uniquely identifies each route. A newly created route won't have a route identifier, so it won't be usable for linear referencing. Because the newly created route is selected you can edit its attributes to set the route identifier.

To edit the route's attributes, click the Attributes button on the Editor toolbar. Click the route identifier field (in this example it is ROUTE1) and in the Value column type the unique identifier for this route (in this example “40001777”).

When you created the new route, you accepted the default method for setting the route measures. This method accumulates the geometric length of the input line features and uses the length as the measure. Because the coordinate system of the feature class is State Plane Feet, the measures on the new route are in feet. However, the measures on all other routes in the feature class are in miles.

To convert the measure values you will apply a conversion factor to them. The newly created route should still be selected. If it is not, select it. Click the Task dropdown arrow on the Editor toolbar and click Modify Feature. You'll see the vertices of the route.

The selected feature is now loaded into the edit sketch. If you click the Sketch Properties button you can see the measure values for each vertex (in the M column).

Right-click anywhere over the edit sketch (you know you are over the line when the mouse pointer changes), point to Route Measure Editing, and click Apply Factor.

To convert from Feet to Miles, type 0.00018939 in the Factor text box and press Enter on the keyboard. To convert between other units type the appropriate conversion factor.

At this point, you have only made changes to the edit sketch, not the route feature. Press F2 to finish the edit sketch. Alternately, right-click anywhere over the edit sketch and click Finish Sketch.

Your route measures are now in miles. You can verify this by double-clicking the selected route to bring it into the edit sketch, right-clicking anywhere over the sketch, and clicking Properties.