Ambulances in Denver are using a new tactic to clear the roads as they rush to an emergency: subwoofers. The vehicles are equipped with 100- and 200-watt speakers pointed at the ground that blast a low frequency strong enough to vibrate the concrete—an unmissable signal for drivers to move out of the way when lights and sirens alone are not enough, reports the Denver Post. "People can feel it throughout their car. It's pretty neat," said the chief paramedic.
The Colorado city tested the subwoofers with a dozen ambulances for more than a year and a half before making them standard issue. Denver paramedics field an average of 230 emergency calls a day, and the police hand out more than 70 tickets a year to people for failing to yield to ambulances. "I have seen people just keep going 30mph with us right behind them, and there is no way they haven't noticed us," says a fire department spokesman. "It's like people aren't even connected to the outside world anymore."