Dear Dr. Gridlock:

Your article on the Virginia high occupancy toll lanes [Commuter page, Nov. 27] does not address what happens at the northern end of the lanes at Old Dominion Drive.

Since this traffic will be moving at, say, 55 mph, whereas the Capital Beltway moves at jogging pace for several hours twice a day, what happens at the merge other than a horrendous backup on the HOT lanes? At peak times, this could soon make getting off the HOT lanes at any of the Tysons Corner exits a test of gridlock frustration.

What have I not understood here?

— Julian Blackwood, McLean

No driving issue draws as many letters as discussion about merges. Motorists hate everything about them. They hate the engineering that created merges, and they hate the behavior of other drivers in them. And they certainly aren’t crazy about the idea of new merges.

But that’s what we’re in for as the Beltway HOT lanes project wraps up late next year.

Some of the new merges look like wins for commuters. They include the flyover ramp that will take traffic from eastbound Interstate 66 onto the right side of the Beltway’s inner loop, eliminating a very difficult left-hand merge.

The merge at the far northern end of the Beltway where the HOT lanes traffic rejoins the general purpose lanes is another matter. The Virginia Department of Transportation will have to watch that area carefully, just as the Maryland Department of Transportation now needs to watch what happens at the Intercounty Connector’s merge points.

However, there are reasons for some optimism about the Beltway.

Transurban, the company that will operate the new lanes, expects that most of the traffic that will head toward Maryland in the HOT lanes already is heading to Maryland in the general-purpose lanes. On some days, drivers who are willing to pay the toll will choose the HOT lanes because they need a more reliable trip.

Some of the northbound drivers will get off the Beltway before they reach Maryland so they can take the Virginia-side exits at Georgetown Pike or the George Washington Parkway. They should have enough time and space to exit the HOT lanes and move right to reach their exits. (It’s not only the volume of merging traffic but also the amount of lane changing right after the merge that should be of concern.)

Traffic will back up when it reaches the American Legion Bridge. Traffic backs up at the Legion Bridge now. The HOT lanes won’t make that scene any better. But in the near future, they probably won’t make it any worse.

One of the things I like about the HOT lanes concept is that it uses the profit motive — always a powerful tool — to inspire transportation improvements. Transurban needs to satisfy its paying customers, and they won’t be satisfied if they get stuck in heavy traffic near the merge point.

“Our engineers tell me that we’ll use the toll price to the end of the facility to manage that merge point,” said Pierce Coffee, who works on the marketing side of the HOT lanes operation.

It’s the same supply-and-demand idea that will govern the operation of the entire toll road: If congestion increases, the price of using the lanes goes up till more drivers choose to stay in the general-purpose lanes, avoiding the “horrendous backup” that our letter writer fears.

Carpooler’s dictionary

Dear Dr.Gridlock:

I am unfamiliar with the terms “slug” and “slugging” as we have very few traffic problems, unless it snows.

Please explain the above terms.

— Ben Berry, Syracuse, N.Y.

In most of the world’s transportation systems, slugs are worthless. They are counterfeit coins used to pay for transit fares. In the District area, our slugs have great value. They rendezvous at rush hour to create the critical mass of humans per car needed to use the High Occupancy Vehicle lanes. That makes highways less congested for the rest of us.

David E. LeBlanc, who manages a Web site for slugs, says the term originated among bus drivers. You can read the story — and get a lot of other useful information about the procedure also known as “casual carpooling” — on his site,

In the early days, these commuters would cluster at bus stops and wait for a solo driver to pick them up before heading to the HOV lanes. The bus drivers would pull up to the stop thinking they had a bunch of passengers waiting, only to be waved off.

Eventually, the annoyed drivers learned to distinguish between the real bus riders and the counterfeits, the “slugs.”

Dr. Gridlock also appears Thursday in Local Living. Comments and questions are welcome and may be used in a column, along with the writer’s name and home community. Write Dr. Gridlock at The Washington Post, 1150 15th St. NW, Washington, D.C. 20071 or
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