The commission prioritizes how to spend money for state highway projects, and generally oversees the operations of the Utah Department of Transportation.
During Holt's chairmanship, the commission oversaw such large projects as the $1.73 billion rebuild of Interstate 15 in Utah County and the $730 million first phase of the Mountain View Corridor in western Salt Lake County.
"You have a fantastic depth of knowledge about transportation issues. I can't imagine a better person to have chaired this," fellow commissioner Wayne Barlow told Holt as he announced his resignation.
Until Gov. Gary Herbert appoints Holt's replacement, current Vice Chairman Kent Millington will temporarily head the commission.
Of note, Holt has been under contract as a consultant for Sevier, Carbon, Emery and Sanpete counties as they seek to invest in a controversial deep-water-port project in Oakland, Calif., to help ship Utah coal abroad.
He led their recent successful pitch for a $53 million loan from the state Community Impact Board, of which he previously had been a member.
The project has drawn criticism in California from local government leaders who complain it is contrary to public policy there that pushes alternatives to fossil fuels.
It also has raised questions about use of state mineral royalties from federal leases that are intended to mitigate the impact of mining on Utah communities. The port is the first out-of-state investment ever approved by the Community Impact Board.