It’s not pretty out there on I-95 south of D.C., where drivers travel through one of the nation’s longest work zones. Crews are building access points for the 95 Express Lanes. (Robert Thomson/The Washington Post)

The 95 Express Lanes project, a 29-mile road work zone in Northern Virginia, is half done and on schedule to be finished by late 2014, Virginia officials say. The high-occupancy toll lanes in the middle of Interstate 95 should open to traffic in early 2015.

I’ve made a distinction in previous postings between tolling new lanes, like the HOT lanes the Capital Beltway, and tolling existing lanes — the sort of thing that Robert Poole of the Reason Foundation has proposed to finance the rebuilding and upgrading of our entire Interstate system. Drivers hate to pay tolls, but they’re more accepting of tolls if it’s for something new, an element that Poole takes into account in his proposal.

I said that our region has yet to cross the threshold of tolling existing lanes, but in blog comments and letters, travelers have been noting their concerns about the 95 Express Lanes. The southern part of the project will add a new set of lanes, but the northern part will convert the two high-occupancy vehicle lanes into three HOT lanes.

Will that push us over the threshold? No, and yes. Adding a lane and opening the system to solo drivers willing to pay a toll as well as to carpoolers driving for free is an upgrade. It adds capacity and expands choice for commuters. But it’s the situation at off-peak hours and on weekends that generates the most complaints from drivers. Right now, the reversible HOV lanes are open to all traffic outside of commuting times — as long as the driver is going in the right direction. The new system will impose a restriction: If there aren’t at least three people in the vehicle, the driver must pay the toll.

So for drivers who see the HOV system only as extra lanes for off-peak travel — say, on weekend getaways — this is the dreaded threshold. They will have to pay for something they now use for free. You can look at that in terms of transportation politics: Is highway tolling going to substitute for gas tax increases? But there’s also a practical issue. I-95 in Northern Virginia is a notorious bottleneck on weekends, and that’s with free access to the HOV lanes in one direction or the other. How bad will it be if weekenders who hate to pay anything extra to travel avoid the HOT lanes and travel only in the regular lanes?

While I think this sets up a very interesting scenario for 2015, my guess is that I-95 won’t come to a standstill on weekends. Some drivers, including those from the Northeast who are more used to paying tolls than drivers in the D.C. area, will want to pay to bypass all the traffic in the regular lanes. Also, adding lanes of any sort — tolled or untolled — is going to have at least a temporarily beneficial effect on traffic, because of the increase in highway capacity.

While there won’t be an limit on how high the tolls can go under this variable tolling system (like the one on the Beltway), the private partners who are building and operating the lanes have an interest in keeping the drivers’ price affordable, because they will need those customers to support their business. Despite drivers’ protests, it’s unlikely those lanes will be empty in 2015.