I remember in 2009 or so there was a case in Berlin (a city in Germany) where someone made way for an ambulance by moving their car on the sidewalk. They did that moving very fast, killing a pedestrian.
Proves that even a very terrible driver can be able to make way for an ambulance.
Also, when a share of the people die on the way to the hospital, the least healthy ones get culled from the the statistics. Some of the people why die into ambulances in USA would die in the hospital in Germany.
The multiplier of 1,5 can therefore also tell about a lot of people dying because of ambulances being stuck in traffic jams. Only the healthiest will make it to the hospital.