Research shows that SUVs reduce capacity and slow traffic on today's roadways. Research performed by the University of Texas at Austin demonstrates that SUVs occupy the equivalent space of 1.2 passenger cars, which reduces the capacity of signalized intersections. Additionally, SUVs require more time to start moving at signalized intersections, reducing the number of vehicles that can get through an intersection. This may be due to the reduced handling and lower power-to-weight ratios found in SUVs compared to passenger cars.

Researchers suggest that the reduction in capacity due to SUVs and other trucks of comparable size will lead to a 10 percent reduction in overall signalized intersection, through-traffic, capacity. "When a network is already operating close to capacity for an hour or more each day, such a decline can mean severe bottlenecking and gridlock." The researchers add that SUVs also cause unwanted environmental and safety impacts.

The problem, and the solution, may lie in the fact that current road capacity recommendations do not account for the popularity of SUVs. The Highway Capacity Manual, Third Edition (Transportation Research Board, Washington, D.C.) distinguishes heavy- and medium-duty trucks, but not SUVs. This leaves traffic planners and engineers with no means to distinguish between cars and SUVs, even in areas with high percentages of SUV traffic.

By adjusting parameters, planners may be able to design signalized intersections that more accurately accommodate the traffic that flows through them.