Braceras said it amounts to the longest continuous stretch of high-occupancy vehicle lanes in the country.
He said UDOT is conducting studies that could allow more express lanes in Davis and Weber counties; funding sources have been identified for possibly adding segments in Davis County.
Speeds in express lanes average 5 to 7 mph faster than in general-purpose lanes, Braceras said. They have 4.5 percent of all accidents but carry 10 percent of all traffic.
He said in some places during peak hours, express lanes carry almost twice as many people because they average 2.2 people per car while general-purpose lanes average 1.1. Braceras said that helps decrease congestion in all lanes, while providing incentives to carpool.
However, he presented statistics showing that 17 percent of people in the lanes are there illegally.
UDOT has said the federal government expects violation rates to be between 8 percent and 15 percent. If rates stay high and the state does not make significant efforts to lower them, it could face sanctions.
The Utah Highway Patrol recently had a three-day blitz to ticket express-lane violators and to draw more attention to rules about who can drive in the lanes legally. Braceras said three or so blitzes are planned per year.
Studies show that 60 percent of the traffic in express lanes are carpools of at least two people; 18 percent are single-rider vehicles whose owners pay tolls through electronic readers; 4 percent are "clean fuel" (hybrids or natural gas) vehicles; and about 1 percent are motorcycles or buses.