Some drivers are skeptical of a Virginia Department of Transportation plan to to expand the HOT lanes network onto Interstate 66 in 2017. (Molly Riley/AP)

Suburban Virginia is one big laboratory for behavior modification among commuters. And I think some of the commuters are starting to feel like lab rats.

For transit users, an experiment began with the opening of Metro’s Silver Line. Could commuters be induced to abandon some highways and some Orange Line stations for the new route? For road users, the big thing is to see how they react to tolling as it becomes more widespread.

It looks as though it will be years before we know the results, because neither project is done, but the highway plan is moving along more quickly. The next phase will be the opening of high-occupancy toll lanes on Interstate 66 inside the Capital Beltway next year.

Toll-road planners are trying to get more people to commute via the interstate, while also holding on to many of those who use it already. If the plan works as designed, everybody benefits. Some who see the experiment from street level, though, have their doubts.

Dear Dr. Gridlock:

Has anyone done a study on the impact of I-66 tolls on the streets of Arlington as drivers use alternative routes such as Lee Highway (Route 29) and Arlington Boulevard (Route 50) to avoid paying tolls? Not to mention all the other side streets drivers will use to cut through.

As someone who can’t use I-66 because I can’t meet the HOV2 requirement, I know that the side streets are already packed. I don’t know how these roads will handle more traffic from those trying to avoid tolls. Are we just shifting traffic from I-66 to other roads?

Carol Burnett, Arlington

DG: Virginia Department of Transportation planners have studied the potential impact of replacing the High Occupancy Vehicle lanes with HOT lanes. They find that some of today’s I-66 drivers may abandon the highway, but many more travelers will be drawn to it.

Who might leave I-66 to avoid paying tolls? It’s not today’s carpoolers. Anyone who carpools in the HOV lanes is not going to use Arlington streets to avoid paying tolls, because they won’t be paying tolls. That’s how high-occupancy toll lanes work.

The theory is that more commuters can and will use I-66. VDOT officials estimate that they can increase the capacity of I-66 by 40,000 people a day. They give several reasons: The variable tolling is meant to manage the flow of traffic so everyone moves at a steady speed. Some solo drivers who now travel on Routes 29 or 50 because it isn’t legal for them to drive in the HOV lanes might be willing to pay the toll to use I-66 legally. And a big chunk of the toll money will go to support more carpooling and more commuter bus riding, which should encourage more of those long-distance commuters to use I-66 without greatly increasing the number of vehicles on the interstate.

Who might leave I-66? Solo drivers of hybrid cars who can use the HOV lanes won’t be able to drive free in the HOT lanes. So they’ll either bail out, pay the toll or get into a carpool or bus.

Also, the hours for the HOT lanes will be a bit longer than the hours for the HOV lanes. So early and late solo drivers would have to choose among paying the I-66 toll, carpooling, bus riding or driving solo on another route.

VDOT planners also expect the HOT lanes plan will reduce the number of cheaters who now drive solo on I-66 during the HOV hours. If so, the cheaters will face the same options as the solo hybrid drivers: Pay the toll, carpool, ride a bus or find another route.

All that said, the nine congested miles of I-66, with its rush-hour HOV system, offer unusual challenges for planners. VDOT officials say that if an unanticipated traffic problem does affect some other routes in the I-66 corridor, they can spend toll revenue to address that.

A last blast at winter

This wasn’t a truly harsh winter, but the memory lingers. This letter may help prepare for the snows of years to come.

Dear Dr. Gridlock: I suppose no good deed goes unpunished. While walking my dog after a small snowstorm [in late February], I realized that it would have been much better if (most of) my neighbors and I had not shoveled our sidewalks. At night, the runoff from the melting snow from front yards froze on the sidewalks. Walking on snow is definitely safer than walking on ice!

During and after the blizzard, the snowplows generally did not dump snow in driveways. However, they dumped large amounts on sidewalks, especially at intersections.

We have good Samaritans in my neighborhood who clear snow from large stretches of sidewalk. But even snowblowers couldn’t remove those mounds on sidewalks that had been cleared of snow until the plows came.

Ted Hochstadt, Pimmit Hills,Va.

DG: Blizzards are rare, but those small storms, followed by melting and refreezing, are more common. Good-deed-doers, don’t give up on shoveling sidewalks. But do keep a bag of rock salt handy to treat that slick surface in the morning.