Not to throw a spanner in the works or anything, but I'd hazard a guess that most of the time, a siren isn't even needed for most responding vehicles. We use it pretty sparingly - but then we live in a mostly rural area. Most of the time we don't run lights and sirens en route to the hospital because it seems counterproductive. Many motorists just get that 'deer in the headlights' thing and freeze. Then you have to stop behind them and it slows you up even more. The one thing that really gets my goat is when people just don't pull over at all - like you are somehow invisible behind them.