Measuring Road Length

Different state and federal reports require a road's length to be measured in different ways.  For example, Certified Public Mileage (CPM) is calculated using only centerline miles.  However, the State Highway Systems (SHS) Log provides information for both centerline miles and maintenance lane miles.  This page defines the different ways road length is measured in federal and state reports.

Centerline Miles represent the total length of a given road from a start point to an end point.  The mileage does not include the width of the roads.  

For example, in the image above, both of the highlighted portions of I-10 and McDowell Rd. have the same centerline miles even though I-10 has more lanes and is much wider than McDowell Rd. 

Lane Miles, or "mainline" miles, are the length of the roadway (i.e. centerline miles) multiplied by the number of through lanes.  In the image above, I-10 is 50 lane miles (10 centerline miles x 5 through lanes) while McDowell Rd. is 20 lane miles (10 centerline miles x 2 through lanes).

The Highway Performance Monitoring Report (HPMS) includes lane miles calculations for the cardinal direction of public roads. 

Maintenance Lane Miles, also referred to as "maintained lane miles" or "total travel miles," is the total length and width of the entire roadway surface.  Unlike lane miles, maintenance lane miles account for the total width of the roadway, including through lanes, auxiliary lanes, and ramps.  For more details on the difference between through lanes and auxiliary lanes, see the Types of Lanes glossary page. 

Maintenance lane miles are not included in the HPMS report.  However, they are used in other ADOT reports, including the State Highway Systems Log.  The measure is also used internally by ADOT for roadway asset management and maintenance operations.