Imagine one or two new lanes on the entire Maryland portion of the Capital Beltway, on Interstate 270 and on I-95 between Washington and Baltimore. These would never be built because they would cost billions of dollars ($67 million per mile), except for a new twist on an old concept: express toll lanes.

Maryland is thinking about expanding all of the above, with 60 percent to 90 percent of their cost paid for from toll collection, according to Neil J. Pedersen, Maryland State Highway administrator. But unlike long-established toll roads, where everyone pays, these would offer commuters a choice of faster toll lanes or slower free ones.

"If a parent is late to pick up a child, or if a plumber has an appointment, it may be worth it to pay a little for express service," Pedersen said.

Here's how they'd work: Build or convert lanes, and separate them with barriers. To simplify enforcement, every vehicle in the express lanes would pay a toll (unlike Virginia's high-occupancy toll -- or HOT -- lanes, where car and van pools would be free).

Drivers would have tolls deducted from an E-ZPass transponder or be billed via an overhead camera recording license plates. There would be no slowing to collect tolls.

Maryland is considering building express toll lanes -- one new lane and a conversion of an existing one -- in each direction on I-270 between Route 124 and Frederick.

Folks who live in that corridor have a chance to find out more during highway administration open houses this week, Tuesday at Martin Luther King Middle School, 13737 Wisteria Dr. in Germantown, and Wednesday at Ballenger Creek Middle School, 5525 Ballenger Creek Pike in Frederick.

The meetings are from 5 to 8 p.m.

Matters are in the discussion phase, but with community support, the requisite environmental impact studies and all else going well, some of these new lanes on I-270 and elsewhere in the state could be in place by 2010, Pedersen said.

These were among the updates I received during a recent lunch with Pedersen and with Dave Buck and Valerie Burnette Edgar, spokesmen for the highway administration, at an Anne Arundel County restaurant improbably named Timbuktu. (Good crab cakes, though.)

Here are some other updates from this trio regarding commuter corridors in our area.

* The intercounty connector: Environmental studies are underway on two possible routes for a six-lane highway between I-370 and Laurel. The goal is to begin construction by 2006 and finish by 2010. For more information, log on to www.iccstudy.org.

* Route 29: The state is replacing traffic lights with interchanges near Blackburn Road/Dustin Road (complete in May 2005); Randolph Road/Cherry Hill Road (complete in September 2005); and Briggs Chaney Road (complete in October 2007).

* Route 210: Maryland has plans to replace the first six stoplights south of the Beltway with interchanges but has no funding to build them.

* Route 5: The state would like to replace stoplights with interchanges at Surratts Road, Burch Hill Road/Earnshaw Road and Brandywine Road. However, there is no funding for them. A Route 5 bypass around Hughesville will be started this fall and should be finished by 2006. There is no consensus about where or whether to build a Waldorf bypass.

* Route 4: Resurfacing between the Gov. Thomas Johnson Bridge and Route 765 will get underway in late summer.

Given the commuter congestion, the Route 4, 5 and 210 corridors seem to deserve more agency attention. Express toll lanes, perhaps?

You can follow the progress of state projects by logging on to www.marylandroads.com or by calling 800-323-MSHA.

SmarTrip Parking Payments

A reminder that Metro is requiring its parking customers to pay with SmarTrip cards starting tomorrow. The cost is $5 per card, plus the parking fee. You can also use the cards for bus and rail travel.

SmarTrip cards can be obtained at each station where Metro has parking. They are near Farecard machines.

Attendants are supposed to be on hand to aid confused customers.

Transportation researcher Diane Mattingly contributed to this column.

You can write to Dr. Gridlock at 1150 15th St. NW, Washington, D.C. 20071. He prefers e-mails at drgridlock@washpost.com or faxes at 703-352-3908. Include your full name, town, county and day and evening telephone numbers. Dr. Gridlock cannot take phone calls.