Parking moves online

Looking for a parking space is about to get much easier, at least for San Franciscans. Later this year they will be able to use cell phones to access a live online map of where spaces are free in the city, thanks to a huge network of sensors.

The devices include a magnetometer that picks up the change in the magnetic field caused by a parked cars. False positives are possible, so there's also an array of other sensors within each device to monitor parking spaces. There are no details yet on exactly what those sensors are.

The network is impressively easy to set up. "Cities can simply glue the [devices] to the street and have a working system almost instantly," says Jim Reich, the vice president of engineering at Streetline, the company behind the new system.

Because it is a wireless mesh network, there's no need to program in or connect new sensors directly, they just join in with the others.

The city hopes that easier parking will reduce traffic congestion, preventing drivers going round in circles in search of elusive free parking spots.

Others are not so sure. If parking becomes easier, the result is likely to be more traffic - not less - thinks Yossi Sheffi at MIT. He says London's congestion charge is a better way to reduce the number of cars on busy city streets.