Roadway surface is calculated using two main measurements in the United States. Centerline miles and lane miles are the tools with which local, state and the federal government determine the size of an important part of the nation's infrastructure. Each has its role, but they are most often used in concert to ensure accuracy in measurement.
Centerline miles are used to measure the length of roads and highways throughout the United States. Centerline miles represent the total length of a given road from its starting point to its end point. The number and size of the lanes on that road are ignored when calculating its centerline mileage. Centerline miles can vary slightly between one side of a divided highway. To gauge the overall length of roads, centerline mileage provides a more accurate number than lane mileage. (If there are only 10 miles of roadway in a given city but it all consists of five-lane highway the lane mileage will amount to 50 miles, which might be misleading.)
Lane miles are used to measure the total length and lane count of a given highway or road. Lane miles are calculated by multiplying the centerline mileage of a road by the number of lanes it has. Lane mileage provides a total amount of mileage covered by lanes belonging to a specific road. In some cases centerline miles are being phased out in preference of lane miles. For example, New Mexico's "Government Accountability Act" states that centerline miles will no longer be used in determining the amount of maintenance and preservation dollars earmarked for each region. Lane miles instead provide more useful although not always more accurate measurements for the purposes of maintenance by factoring in multiple lanes and the additional work they may require.
Government status reports and plans may list their proposed infrastructure construction projects by using the terms centerline miles and lane miles. For example, Indiana Governor Mitch Daniels proposed that "375 centerline miles of new roadway will be constructed" by the end of the 2012 calendar year in a 2005 plan. This means that 375 miles of roadway will be constructed in total without regard for lane count or location. Governments also use the terms centerline miles and lane miles to measure the extent of state highway and roadway systems. For example, the state of Florida reports its total lane miles as increasing from around 39,000 to around 43,000 between 1999 and 2009.
Centerline miles and lane miles can be used to determine the distribution of roadways throughout a state or city as well. These figures can then help officials to regulate maintenance projects and funding. Washington state lists its total 2007 centerline miles at 84,432 and lane miles at 174,433. These numbers are then broken down into categories by jurisdiction including city, state, county and other. They are further broken down according to the percentage of overall state traffic that each one carries on average per year. Separating the roadway surface into jurisdictional categories helps ensure that the financial responsibility for each is accurately accounted for.
- Florida Department of Transportation: Florida State Highway Lane Miles
- Indiana Department of Transportation: Major Moves
- Washington State Department of Transportation:How Many Centerline Miles are in Washington?
- New Mexico: Maintenance of the Highway System
- Midwest Regional University Transportation Center: Estimating Cost per Lane Mile...; 2011
- U.C. Berkeley; Department of Public Works; Pothole Politics; William A. Robinson
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