A view of one an ExpressToll lane in metro Denver. Starting Jan. 1, 2017, drivers will need two passengers to use the lane for free.

(Courtesy CDOT)

If you and a passenger use the Express Lanes on Interstate 25 or U.S. 36, you'd best find another rider -- and soon.

Starting Jan. 1, 2017, the Colorado Department of Transportation will require drivers to carry two passengers -- for a total of three people in a car -- to avoid paying tolls in Express Lanes. That's up from the current requirement of just one passenger.

CDOT spokeswoman Amy Ford says there are plenty of options for traveling the state's highways while avoiding tolls, including buses and carpooling apps. 

Interview Highlights With Amy Ford

Why the change was needed:

"The goal of our express lanes is to move people and to move them reliably. And obviously we manage our traffic on those lanes by pricing with tolls. And so the higher you put a price on the toll the less people use it and you lose the benefit of the lane. And the lower you put it, everyone uses it and it clogs up and no one gets that benefit. And so we always hit that sweet spot. Well, free use of the lane through HOV is another piece that impacts the reliability of the lane."

On whether the HOV3+ rules will lead to fewer cars in the Express Lane or more people paying tolls:

"I think you could see a combination of both, to be very honest. ... The result we think will happen, is some people continue to drive in the lane and they will start paying the toll. Others will decide nope, they're going to move into the general purpose lanes. So we may see some increase in traffic on the general purpose lane."

On "slugging," an unusual method of avoiding tolls:

"Colorado is actually one of seven states that has [HOV3+]. And in some of those states, Virginia for instance, they do something called 'slugging' where people stand in a certain area. A car comes by and picks him up and that gets them to three -- and then they drive the lane for free. So we're even exploring some of that and how we promote some of that."

On other carpooling tools:

"DRCOG, for instance, has a carpool matching site that they can use. Uber is going to look at extending their program up in the [Boulder] area where they use technology to more easily match people on the road. ... Lyft has a program as well."