That's the sound of an electric car. I was lucky enough to drive one this week when Ford brought its electric Focus and Transit Connect van to a dealership in Manhattan. Inside the cabin, the only sound was the other traffic on the road.

The Focus relies on a lithium ion battery pack to silently convey you up to 100 miles. That's the same battery burning your lap when you use your laptop computer—a primary reason Ford uses liquid to cool the pack. But the car boots up and shuts down a lot faster than a computer when you press the button. And there are no gears to shift—it's all torque from the second you press down on the accelerator.

The car will take six hours to recharge from a home outlet—outsourcing pollution from your tailpipe to your local power plant, where it may be easier to control. That recharging might even start troubling the grid if the quiet cars prove popular enough over the next decade. Already, the Nissan LEAF and Chevy Volt are ready for sale and the electric Ford Focus will join them next year.

All of which means roads in some places could get a whole lot quieter. So do be careful crossing the street.

—David Biello