Traffic Tamers

THE ENTIRE EBB and flow of the rush-hour experience is orchestrated in a windowless bunker at the edge of downtown, the Department of Transportation's Traffic Management Center (TMC). It's the command post of the city's traffic theater.

The building stands on the edge of the freeway in the southeastern corner of downtown Minneapolis, and during the peak driving periods, it's cut off from the rest of the city by dense lines of stop-and-go. The control room itself is lit almost entirely by the glow of 176 television screens banked floor to ceiling along two walls; 128 are small black-and-white monitors with fixed images. The rest flash a sequence of closed-circuit images broadcast from hundreds of television cameras mounted on 50-foot poles, each one capturing a mile-long view of freeway traffic, 176 flickering images of cars rolling rank-and-file over the road.

If all the cars that pass every day over Twin Cities freeways sat bumper to bumper, the line would reach handily to the Atlantic. Instead, the cars sift back and forth morning and evening, speeding and slowing, ramping up to highway velocity and crawling past crashes.

It's the primary duty of the TMC technicians hunched over their glowing workstations to control the flow of cars coming on the freeway and to keep the road clear of problems: Cars stall; the wiring harness malfunctions, or the alternator. Tires blow. Engines catch on fire. Frequently, cars run out of gas. Two of the technicians monitor the rates of the on-ramp stoplights. The information officer relays traffic incidents to the State Patrol and the drive-time radio helicopters. A fourth works the Incident Data Capture Work Station. A fifth describes road conditions in radio inflection on KBEM.

16:34."We've got some furniture on I-94 at Dale. It looks like a beige sectional, or a pair of chairs. One of them is intruding into the left lane of traffic, eastbound."

The information officer twirls a black joy-stick and the view on her screen zooms in on the furniture. Fast-lane commuters flash the brake lights on camera.

"Did he hit it?"

"He hit it."

Two minutes later a yellow truck parks there, one of dozens of Highway Helpers dispatched from the TMC to manage traffic incidents: push stalls to the shoulder, get stranded motorists on the road again, clear the road of debris. Nothing surprises the Highway Helpers. Objects they have cleared in recent months include beer off a truck, a coffin, a hot tub. Animals of all kinds wander onto the freeway. Once a live chicken, and once a truckload of chicken guts off a semi.

On screen, the Highway Helper loads the couch sections into the truck. The camera pans back, and the screen again matches the rest.

16:49. A semi stalls, blocking traffic on 494. One of the men mouse-clicks the message on an enormous overpass sign to warn commuters. "By 5 p.m.," someone comments, "that will be backed up a mile."

16:54. Stalled bus on the entrance ramp.

16:55. Three-car accident blocks the center lane on 35W at 280.

Once, a car stalled by the roadside with a driver and passenger inside burst into flame. All they could do at the TMC was watch the fire burning into the screen.

Besides dispatching Highway Helpers, the technicians at the TMC control the flow of traffic with stoplights on the on-ramps. Detectors count cars on the highway and feed the information back to computers at the TMC. The entire freeway network is broken up into zones of about six miles. The computers interpret the data for each zone using a Real-Time Volume Based Zone Control Equation--at the TMC, they call it The Algorithm. On paper, The Algorithm looks like this: (A + U - X) + (M + F) = B, where A is congestion at the beginning of each zone. U is the number of cars coming on the freeway from unmetered ramps. X is traffic exiting the freeway. M and F are two kinds of metered ramps. B is the "downstream bottleneck capacity volume"--how many cars the road can hold.

In cases of accidents, stalls, debris, patches of ice, loose chickens, or other hazards--artificial bottlenecks, as it were--the technicians can alter the ramp meters manually. On their computer screens, each ramp meter appears as a tiny string of numbers--hundreds running in columns down the screen, color-coded (red for slow traffic, green for clear sailing). A few keystrokes can madden the commuter at the head of the line, or make her day.

17:21. It's darkening now. Color leaches off the televisions, and out of the sky outside. Identifiable forms melt into patterns of light and dark. Headlights stack diagonally across the screens. Traffic is peaking. The radio crackles. The DJ puts on his headphones and swings around toward the mic. Keyboards clack. One television camera stares close-up at a pair of pulsing tail lights. The rest flash mile-by-mile up and down the freeways, cutting from one scene to the next like a secret code, the hidden language of gridlock.

In the right lane on the Crosstown, a station wagon clots a lane of traffic. The TMC information officer zooms in. A woman in heels and miniskirt slams her car door and fights, wind-whipped, along the shoulder. A few paces ahead of her, a limousine waits. The camera pans along with her, its angle high and distorted. For a minute, she looks flattened against the concrete. She climbs into the passenger's seat. Then the limousine noses into traffic, and is lost in the forward motion.

 
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