HOV lanes in Utah require at least two passengers, or allow use by single riders if they buy a C-decal available for clean-fuel vehicles or buy a transponder to pay tolls.
Rep. Steve Handy, R-Layton, sponsor of the bill, said UDOT is issuing about 85 C-decals a month and has issued 3,800 overall. Those clean-fuel cars now account for about 4 percent of all HOV-lane traffic.
"UDOT is concerned that with the explosion of growth in C-decal vehicles, our HOV lanes could become degraded as defined under federal law," with average speeds under 45 mph he said.
If that occurs, he said the federal government could order action to rectify it, including raising the required number of passengers in carpools or stopping use by toll-payers or clean-fuel cars.
Hull said Utah is not close to the point of degradation yet but wants to have rule-making authority to prevent problems.
"The goal of the HOV lane is to encourage people to carpool," she said. "We have a little excess capacity in that lane because we don't have enough people carpooling yet. So we started the Express Pass program so we could sell off that excess capacity to single-occupant vehicles for a toll," or by selling C-decals as an incentive to buy clean-fuel cars.
When lanes are too crowded, the state raises tolls to encourage transponder users to move out of the lanes. It's different with C-decals. "Once that vehicle has that decal, we have completely lost control of that vehicle. We can't control how many get in, when they get in, how often they get in."
A few lawmakers opposed the move, saying it could discourage purchase of such vehicles.
Hull said such encouragement "is a very laudable goal. But remember that the goal of the HOV lane wasn't to encourage people to buy a clean-fuel vehicle. The goal of the HOV lane was to encourage people to carpool." She said UDOT would be thrilled if so many people were carpooling that C-decal and toll users were no longer allowed.
Likely a bigger incentive than HOV lane use for buyers of clean-fuel vehicle is the money they save on fuel, Hull said.