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 mph from 30 mph as early as mid-October. The reduction is a central component of Mayor Bill de Blasio's "Vision Zero" traffic safety plan to reduce pedestrian fatalities, along with speed humps, improved roadway designs, new cameras to catch rulebreakers and much more to confront dangerous behavior at the wheel.

"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," says Ryan Russo, an assistant commissioner.

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 is the principle that no level of traffic efficiency is worth a single pedestrian death.

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 don't necessarily want it to flow. We want it to move, but we don't want it to move at excessive speeds," said John Tipaldo, the director of systems engineering, whose PhD dissertation focused on pedestrians.

When the new limit takes effect, signs will be posted at about 150 so-called gateways to school motorists. An ad campaign will blitz the airwaves, Internet, and billboards. Cops will patrol to ticket speeders and red-light runners and surreptitious cameras will be deployed to automatically ticket violators where cops aren't necessarily watching.

In the command center -- in a city office building near Queensboro Plaza -- traffic engineers and other city personnel monitor walls of surveillance video 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 color-coding midtown traffic, recommends in real time the optimal way tweaks; the engineer on duty decides yes or no. 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% to 5% who break the rules.

"We're trying to remove the incentive to speeding," said Tipaldo.

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 DOT spokesman Nicholas Mosquera.

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

To nab and discourage motorists who disobey traffic rules, engineers are deciding where to put new speeding 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.

The city is also authorized by Albany to install up to 140 speeding cameras near school zones -- 20 are in place so far.

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