ISouthbound I495 with the new hot lanes to the left, Monday November 19, 2012. (Dayna Smith/FOR THE WASHINGTON POST)

Dear Dr. Gridlock:

I am glad that the 495 Express Lanes are done, but I am somewhat surprised by the configuration. I thought one of the reasons for the Beltway express lanes was that if a driver encountered heavy traffic, he or she could make an immediate decision to get out of it by entering the express lanes.

However, it does not appear that once you are on the Beltway you can get in the new lanes without exiting the regular lanes first. Why did they not allow entrances from the far left lane of the Beltway into the Express Lanes at regular intervals? This would allow individuals to move away from heavy traffic situations much more quickly.

— John White, McLean

I imagine many drivers who have heard of these Express Lanes thinking, how tough can this be? I know where the Capital Beltway is. These are four new lanes in the middle of the Beltway. I don’t even need to look at a map.

But White is highlighting one of the fundamentals Beltway drivers need to understand to make the best use of the new lanes: Most of the entrances and exits are at interchanges rather than along the Beltway itself.

Commuters usually won’t be able to make decisions about whether to use the toll lanes while they are in the regular lanes. Unless they are at the very start or the very end of the lanes, they can’t look up ahead to a point where they see a lot of brake lights and decide it’s time to slide over for an express ride. There aren’t any gaps in the white bollards.

This setup is utterly unfamiliar to the D.C. region’s drivers. The specialized lanes that we understand are the High-Occupancy Vehicle lanes set aside for carpoolers. Along most of those routes, drivers can slip in and out of the HOV lanes. But this new setup takes more planning to use.

In fact, our new express lanes, also know as high-occupancy toll lanes, represent some highly unusual challenges for commuters and the people who operate them.

Peter Samuel, the editor of the Web site, which monitors developments in the toll road industry, said that the dynamic tolling system — raising the price to lower the congestion — is noteworthy but has been used elsewhere.

“The 495 Express Lanes are a first not in the dynamic pricing as such, but for using such pricing in a very ambitious and complicated format with so many entries and exits,” he said.

“Nowhere else is there a tollway within a freeway like the 495 Express Lanes equipped entirely with dedicated on- and off-ramps, and a lot of them catering to shorter trips as well as longer. Most others force users to enter and exit via the free lanes, weaving across the traffic. Or else they are long pipes, catering only to long trips.”

Makes you feel like a pioneer just for turning the ignition key. But why didn’t we wind up with one of those “long pipes”?

Pierce Coffee, an executive with Transurban, operator of the Express Lanes, said the design had to account for Beltway space and the flow of traffic, among other things.

A setup with ramps allowing traffic to slip back and forth would require an even wider Beltway to allow for safe merges, she said: “One of the benefits of express lanes was the limited right of way needed to complete the project.”

But think also about the goal of providing a reliable trip in the pay lanes of at least 45 mph, Coffee said. The more holes you poke in the Express Lanes, the more you increase the potential for backups and slowdowns as vehicles have to merge, and that would affect those lanes as well as the regular lanes.

Picture drivers entering the Beltway on the right and then sliding across the four regular lanes so they could reach a merge point into the Express Lanes. Plus, drivers might have to give up some of the new access points, at Route 29 and at Westpark and Jones Branch Drives in Tysons to create space for more merges with the regular lanes.

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 e-mail