Story Highlights
  • Segment of I-15 with most carpool violators is between Draper and Midvale, whether it's morning or afternoon rush hour
  • In morning rush hour, anywhere from 25 percent to 33 percent of HOV lane users from Lehi to Midvale are breaking rules
  • Engineers suggest an increase in enforcement, education and tolls to help curb the problem
Research to increase rush hour HOV speeds finds many non-carpoolers in express lane

Newly published research from BYU civil engineers finds that up to 25 percent of drivers in Utah’s high occupancy vehicle (HOV) lanes during rush hour are violating carpool requirements.

The two segments of I-15 with the most single occupant violators in the morning won’t surprise commuters: Northbound between 14600 S. and 7200 S. (33 percent) and northbound from Lehi Main Street to 14600 S. (25 percent).

“The sections of I-15 with the most HOV violators are the sections where there is the most congestion,” said study lead author Grant Schultz, professor of civil engineering at BYU. “With education and enforcement, those areas can improve.”

For the afternoon rush hour, the same Midvale-to-Draper section of I-15, but in the southbound direction, had the most HOV offenders (21 percent), followed by the southbound segment from 2300 N. to 7200 S. (also 21 percent, when rounded up).

The research was done in conjunction with the Utah Department of Transportation and is aimed at finding ways to improve HOV lane speeds. The goal is to keep carpool lane speeds above 55 mph during rush-hour traffic.

Schultz and his students tracked HOV lane traffic during morning and evening rush hours along I-15 from U.S. 6 in Spanish Fork all the way to the 2300 North in Salt Lake City. They also tracked the lanes during off-peak times for comparison, between noon and 2 pm.

To track the express lane users, the researchers used the “floating car method” by driving in the third general purpose lane about 10 mph slower than other vehicles and tracking the vehicles as they passed by. Researchers documented which vehicles used express passes or had clean vehicle decals and how many people were in the vehicles.

“We were that guy,” Schultz laughed. The researchers drove thousands of miles collecting the data and calculated they did the equivalent of a road trip to St. George—and back—on one particular day.

After collecting the data and running several analyses, the researchers identified three ways to reduce volume in Utah’s express lanes and thus improve the average speeds:

  • Reduce violation rates through increased enforcement and education campaigns regarding policies related to the proper use of the express lanes
  • Increase tolls during peak periods, including an increase in the maximum allowable toll
  • Increase the HOV limits in the express lanes from 2+ to 3+ per vehicle in peak periods

Schultz’s team projected morning rush hour speeds could increase nearly 10 mph with the combination of effective education, enforcement and an increase in the maximum toll rate. UDOT has already acted on the recommendation, working to increase enforcement and education. However, current construction in some of the highly-congested sections of I-15 has put things on hold.

“The only way to increase speeds is to reduce the volume,” Schultz said. “That said, humans are only willing to drive so much faster than the lanes next to them when congestion is high—there is always the risk of someone pulling out into the HOV lane.”