Improved technology and better data collection methods prompted the update, according to a statement from the administration.
VMT refers to the number of miles vehicles travel over a given time period. It is routinely used to measure traffic on America’s roads and bridges and to calculate important statistics such as traffic fatalities, fuel efficiency, and air quality.
The new methodology does not impact annual VMT overall, nor does it affect how FHWA distributes highway funds to states. It does change VMT figures for specific vehicle types, according to the administration. For example, VMT for light-duty passenger vehicles is lower, resulting in a slightly higher fatality rate. VMT calculations for motorcycles, buses, and large trucks are all higher, resulting in lower fatality rates.
“We regularly review and assess all our data programs to ensure we are using the best available information,” FHWA Administrator Victor Mendez. “This is a good example of how we’re able to develop better ways of reporting critical information.”
In the last decade, states have dramatically improved the way they collect travel data thanks to improved technical equipment for counting and classifying vehicles, better federal guidance on how to gather the information, and a move by FHWA and the National Highway Traffic Safety Administration in 2007 to mandate states report data on motorcycle travel.
Simultaneously, the discontinuation of the Vehicle Inventory and Use Survey in 2002 — which was previously collected by the U.S. Department of Commerce and used to benchmark vehicle miles traveled — made it critical to look to other, improved data-collection methods. The new methodology uses more consistent, complete data gathered directly from the states and ensures more accurate calculations for VMT by vehicle type, according to FHWA.
FHWA publishes monthly VMT data at 1.usa.gov/FHWA-VMT.