From a chilly, windowless command center in Long Island City to the Transportation Department headquarters at the tip of Manhattan, engineers are contemplating how to reorchestrate the traffic on the city's 6,000 miles of streets to start slowing it down.

The city's default speed limit will be lowered to 25 miles per hour from 30 mph as soon as mid-October. The reduction is a central component of Mayor Bill de Blasio's "Vision Zero" traffic safety plan to reduce pedestrian fatalities, and includes speed bumps, improved roadway designs, new cameras to catch rule breakers and much more to confront dangerous behavior at the wheel and on foot.

"Human beings are human beings, and they're fallible and they're going to make mistakes, so we're trying to have a transportation system that's forgiving to people's mistakes," said Ryan Russo, an assistant commissioner. "So that if they make a mistake it doesn't cost them their lives or their limbs."

The default speed limit -- which applies where there are no signs indicating otherwise -- will revert to 25 for the first time in 50 years. Last month, at de Blasio's request, the State Legislature allowed the city to move forward with the plan.

Central to Vision Zero, based on a program pioneered in Sweden, is the principle that no level of traffic efficiency is worth a single pedestrian death.

Giving pedestrians time

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New York City already differs from municipalities where pedestrians must press a button to get a signal to cross. The city assumes there will always be pedestrians present and such buttons are rare.

"We give them ample crossing time without having to worry about pushing a button," said John Tipaldo, director of systems engineering for the city Transportation Department.

Most pedestrians cross at 4 or 5 feet per second, but the city assumes a slower rate -- 3 feet per second -- to accommodate children and the elderly.

Traffic could move more efficiently -- the average speed during peak hours in Manhattan is just 10 mph -- if city streets weren't pedestrian-friendly by intent.

"We want it to move, but we don't want it to move at excessive speeds," Tipaldo said.

When the new limit takes effect, signs will be posted at about 150 gateways, such as those on the Queens-Nassau border, to school motorists. Ads will blitz the airwaves, Internet and billboards. Cops will patrol to ticket speeders and red-light runners, and cameras will be deployed to automatically ticket violators when cops aren't necessarily watching.

In the command center -- actually two large rooms in a city office building near Queensboro Plaza -- traffic engineers and other city personnel monitor walls of surveillance videos displaying hundreds of congestion-prone intersections, highways and byways. Police and traffic experts shuttle between terminals to reroute traffic around crashes and stuck vehicles. Midtown in Motion, a computer program that color-codes midtown traffic, recommends tweaks in real time and the engineer on duty decides whether to accept the computer suggestions. With a few keystrokes, engineers can rejigger nearly all of the city's 12,000 signaled intersections.

Vision Zero will alter traffic design, and motorists will need to change their habits as officials target the estimated 2 percent to 5 percent who break the rules. "We're trying to remove the incentive to speeding," said Tipaldo.

Adjusting traffic lights

One strategy is adjusting traffic signals so that drivers rolling along major one-way avenues in lighter traffic don't see an endless stream of green lights ahead. "You can be inclined to go faster if you see nothing but green," Tipaldo said.

"By timing the progression, you can encourage safe, smooth speeds along the corridor," added Nicholas Mosquera, a DOT spokesman.

City engineers will study traffic flow, congestion and other factors to determine where to retime signals.

To nab and discourage motorists who disobey traffic rules, engineers are deciding where to put new speed cameras. Officials hope to keep the locations secret.

"We don't want somebody to slow down to pass the camera, then speed up after he leaves," said Steve Galgano, DOT's executive director of signals, street lighting and systems engineering.

Officials have maxed out on the 150 red-light intersections where they are authorized by Albany to set up surveillance, but can install up to four cameras at each. Right now, there are 190 cameras.

The state also authorized the city to install up to 140 speed cameras near schools -- 20 are in place so far -- which issue the vehicle owner a $50 ticket without license points.

Before the city's new speed limit can take effect, Gov. Andrew M. Cuomo must sign the bill passed last month, and the City Council must pass a law. Both have signaled they will give the green light.