Dear Dr. Gridlock:

I recently noticed some Interstate 66 east lanes are now marked with double solid white lines. The Virginia driver’s manual does not have an explanation for these road markings.

I know in California the 24-hour HOV lanes are marked with double broken lines. The solid lines indicate no entry, and the broken lines mean entry is allowed. The I-66E HOV lanes are not 24 hours, so the lines do not seem to make sense.

Nor does their location on I-66 seem to make sense. Can you shed any light on these new markings?

— Edward Conley, Fairfax

I’ve gotten similar inquiries recently as drivers noticed new markings along I-66 near the Capital Beltway where the Virginia Department of Transportation has been repaving. The drivers welcomed the new asphalt but found the lane markings confusing.

The new double white stripe is meant to improve the flow of traffic in the high-occupancy vehicle lane. A Transportation Department study a couple of years ago found that one reason for slow travel times is the weaving drivers do between the HOV lane and the regular lanes.

The study, in which state police participated, recommended limiting the locations where drivers can move in and out of the HOV lanes in the hope that compliance would lead to better travel times. Drivers are seeing the results of that recommendation in these double lines, marking the areas where there should be no lane changes.

It’s a work in progress. Still to come are signs that read “Do not cross double white lines.” The gaps in the solid lines at certain locations are there to allow traffic to enter and exit the HOV lane, according to Randy Dittberner, VDOT’s regional traffic engineer.

VDOT is going to monitor this new treatment to see if it has the desired result of limiting the weaving. If the double lines work as intended there, the treatment could be used elsewhere in Virginia. If not, I-66’s original marking could be restored.

Motorists are not permitted to cross the double white lines at any time, even outside of HOV hours.

Drivers on some segments of Maryland’s HOV system — I-270 approaching the Beltway, for example — also are familiar with the solid white lines.

I hope the Virginia experiment works out.

And I know what you’re thinking.

Many of the region’s HOV lanes have no barrier to separate them from the regular lanes, and some drivers genuinely get confused about the intent of the lanes as carpool routes. Others are just cheating. They see traffic going faster in the left lane, so they move into it, no matter what the rules are. A solid line won’t stop them, but astate trooper might.

Metro’s standards

Last Sunday’s column featured a letter from Rebecca Johnson of College Park protesting Metro’s plan to adopt a standard on train frequency that she and many others thought was subpar.

She saw a follow-up I did for the Dr. Gridlock blog quoting the revised version of the standard that the Metro board had on its agenda for Thursday’s meeting. The new version said: “Resolved, that the Board of Directors approves headway as a Metrorail service criterion, and sets thresholds such that normal schedule headways will not exceed 15 minutes during peak service, 20 minutes during off-peak service, and 25 minutes during late night service after 10 p.m.”

Johnson said: “Frankly, this leaves me more suspicious than before.” She figured the original wording would relegate the big gaps between trains to periods of track work or to emergencies. “This new wording does shorten the off-peak standard [originally allowing 30 minutes between trains], but it also broadens the applicable circumstances in all periods to the ‘normal’ schedule. Fifteen minutes during peak-hour normal operations? I don’t think so.”

Before Thursday’s meeting, the board did a smart thing and decided to postpone a vote to allow more discussion.

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