By John Kelly
Sunday, March 18, 2007

As you drive into Washington across Roosevelt Bridge, there is a strange vehicle parked off the left lane on the District side just prior to the E Street exit. What is that thing? It has been sitting there for at least five years I know of.

-- Vinson Nash, Washington

"It's called a BTM: barrier transfer machine," Jim Austrich, chief of the District Department of Transportation's systems operations branch, said as he pulled his District-issued SUV onto a median strip on the east side of the Theodore Roosevelt Memorial Bridge one morning last week.

About 100,000 vehicles a day cross the Potomac via the Teddy Roosevelt Bridge. During the morning rush hour, most of the traffic is flowing from Virginia into the District. In the afternoon, the pattern is reversed.

The bridge has seven lanes. Answer Man supposes it could be divided in half -- 3 1/2 lanes headed east, 3 1/2 lanes headed west -- but as very few people in Washington drive half a car, that probably wouldn't work.

Instead, DDOT fiddles with what's called the "directional capacity" of the bridge -- in other words, which direction traffic flows in the center lane. Weekday mornings it's four lanes into the District and three lanes into Virginia. Weekday afternoons, it's the other way around.

Answer Man was there last week to see how they do it.

He stood on an embankment at the bridge's eastern end, the Kennedy Center off to the right. Creeping slowly from the west was a contraption that resembled a subway train car -- the barrier transfer machine.

But first, the Quickchange Moveable Barrier, made by a California company called Barrier Systems Inc. Traffic is separated on the bridge by an articulated concrete wall. It's like a 3,800-foot-long, unfastened bracelet, each link a 600-pound block of reinforced concrete about 3 feet tall, 3 feet wide and a foot deep. The blocks are joined by metal pins and shock absorbers.

As it approached, Jim said, "It's eating the barriers on one side, and they come out the other side."

Indeed it was: eating the barriers with a "mouth" on the right side, lifting them up and excreting them 10 feet to the left.

The top of each concrete block has a profile sort of like a champagne cork. It's that indentation that the barrier transfer machine grabs onto. A pair of rails welded to the underside of the diesel-powered machine are lined with rubber wheels about the size of a Frisbee. The concrete blocks ride up on the rails, roll up and under the machine on the wheels, and get deposited one lane width over. It takes about 25 minutes to do the entire bridge.

The BTM is like the pushmi-pullyu from "Dr. Dolittle." It has a steering wheel on each end and can drive in both directions. About 4 a.m., it goes from east to west, creating an extra inbound lane. About 10:30 a.m., it goes from west to east, creating an extra outbound lane.

When Answer Man was there, Luis Henriquez was on one end and Noe Flores was on the other, each making sure the blocks were carefully lifted and set down. Carlos Hodgson proceeded in a truck, making sure no debris was pulled into the machine. The men work for Flippo Construction, the contractor that handles the lane change.

The barrier has been employed since 2000, when the bridge was widened from six lanes to seven. Why do it this way, and not with signs or overhead lights, as is done with 16th Street NW and on Route 29 in Silver Spring?

"There's a huge, huge issue with safety," Jim said. "If you don't have positive separation and someone loses control -- boom -- you have a major problem."