World War II footage has that familiar black-and-white scene: a heavily damaged war bird lands out of control on the stern of a straight-deck carrier and crashes into a steel cable net, which prevents it from ramming into aircraft waiting to take off. Volunteer firefighter Matthew Gelfand was watching one such documentary in 1993 when a lightbulb went on above his head. He had heard about an accident in which a car struck a train, then another vehicle whizzed past the crossing and hit a firefighter. "If a carrier could catch a plane with a net, why not a car with a net?" Gelfand wondered.

The result is GRAB, for ground retractable automobile barrier. Essentially, it is a tennis net made from Kevlar strips, with two metal stanchions on either side. Remote sensors or a manual push button shoots the net up from a two-inch-wide recess in the ground in as little as three seconds. As the vehicle hits the net, the energy is absorbed by pistons in the stanchions and the net--not unlike the barriers on the WWII aircraft carriers, whose nets had cables that folded down onto the deck and were connected to energy-absorbing stanchions.

This article was originally published with the title Nothing but Net.

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