Originally published on March 16, 2023, by Amanda Abrams for UrbanLand Magazine.

For years, transportation planners throughout the United States calculated the efficiency of roads and highways using a “level of service” concept. Formally introduced in 1965 by the U.S. Department of Transportation, level of service, or LOS, measures congestion, examining the delay experienced by motorists at intersections compared to free-flowing traffic.

For decades, “LOS guided transportation planning in the U.S.,” said Michael Schmitt, a senior sustainability consultant with the planning and design firm Kimley-Horn, at ULI’s 2023 Carolinas Meeting in February.

But while LOS has been a useful tool for measuring car traffic, it has been charged with magnifying sprawl, reducing safe options for pedestrians and cyclists, and leading to induced demand, in which new roads built to ease congestion quickly fill up.

In recent years, another metric, vehicle miles traveled (VMT), has become popular. VMT examines the demand for vehicles on public roads and tends to reward density and complex multi-use areas.

Both concepts have their uses, Schmitt said. But taken together, they illustrate the point that how we measure something is often, intentionally or not, a policy choice that shows up in our built environment.