Delay 'flushes' Baltimore intersection

THE INTREPID COMMUTER

December 27, 1993

Intrepid Commuter had thought we'd heard it all until last week when city officials explained that an intersection needed "flushing."

We can only assume such language is the direct result of the traffic office's posture as a function of the city's public works department. Those are the same folks who worry, among other things, about potties.

But we get a-head of ourselves.

Our inquiry actually began with a letter from faithful reader Charles Hopwood who was concerned about two intersections along University Parkway that are in close proximity -- University and 39th Street/San Martin Drive and University and Linkwood Road.

Traveling east on University Parkway, you will note the two traffic signals for these intersections do not turn green at the same time, the city resident writes.

If you're stopped at the first one -- Linkwood -- you'll be stuck at a red light watching the second one -- 39th Street -- turn green.

"Alarmingly, people eastbound on University stopped at the Linkwood light ignore this light and take the turning green of the 39th/San Martin light to mean it's OK to proceed -- just when traffic is moving forward from Linkwood onto University!," he writes.

"I use this route to go to work, and almost every morning someone stopped at the Linkwood light will ignore it and . . . almost smash broadside into a car turning from Linkwood."

We forwarded Mr. Hopwood's concerns to the public works department where this whole notion of flushing was discussed in considerable details.

Yes, traffic engineers admitted, there's a 10-second delay in the signal changes. But it's there for a purpose.

The timing allows traffic going from Linkwood to clear the area. Without the delay, the cars turning onto University might backup and clog the intersection. This kind of cycle is called a flushing phase.

Vanessa Pyatt, spokeswoman for the department, notes that engineers have tried to make the signal at 39th as visible as possible. The bulbs within the signals are actually about 50 percent larger at 39th than at Linkwood.

"I guess it's possible an occasional daydreaming motorist may inadvertently run the light because he's focused on the second light, but we're more inclined to believe it's deliberate on the part of motorists who are familiar with the area and know the timing of the signals," she said.

So here's the deal. Officials from the public works department have contacted the city police department about enforcing the signals. Don't be surprised to find a friendly police officer stationed there this week.

As for the danger, a look at the police reports shows no serious accidents reported there over the last three years.

Sign's good advice prevents bad tips

Was that sign talking to me?

Intrepid Commuter can imagine the DeNiro-esque internal monologues of truckers -- not that we enjoy engaging in that sport too often -- when they see the State Highway Administration's newest bit of technology.

One of the first of its kind in the country, the interactive sign is designed to warn trucks that they're in danger of tipping on a fairly sharp curve off the Capital Beltway.

Called an "automatic warning system," it was installed less than two weeks ago on the ramp from the inner loop to northbound Interstate 95. Here's how it works.

Sensors buried in the pavement can judge both the weight and speed of a vehicle and that information is relayed in a microsecond to a computer mounted nearby. If a truck is going too fast for its weight -- creating more lateral force than positive force -- the sign goes into action.

The normally black fiber optic sign lights up the warning: "TRUCKS REDUCE SPEED" under an illustration of a truck tipping.

Could such a warning slow trucks before they tip over?

As part of the $317,000 federally financed experiment, the SHA has installed a second set of sensors just past the sign to test the results. The evaluation is expected to take three years.

Twenty trucks have rolled over at the I-95 exit over the last five years. SHA officials hope the sign could save lives and prevent the major traffic problems that truck accidents so often cause.

Two similar signs have been installed along the Virginia side of the Beltway. Like the Maryland sign, they only evaluate trucks. Cars won't trigger them.

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