MONOC recently released a PSA on the effectiveness of lights & sirens & how care is still needed to avoid collisions & injury. It turns out that lights & sirens are not nearly as effective in warning drivers & pedestrians as one might think. This means that the available response time is very small.
MONOC suggests care & vigilance even while driving with lights & sirens. As for speed & aggressive driving, they show how it may result in more patients than those in the back of the ambulance. They even go as far as to suggest regular driving without lights & sirens in certain select cases.
For references & a free copy, visit MONOC.org.