What is the true impact speed when two cars collide head-on at 50mph?

[elemis]

According to the sources I've seen: for a given road, a lower speed limit leads to fewer deaths and less emissions.

Why? Less kinetic energy involved and less energy dissipation per unit distance.

However, it could be argued that since cars have a lower fuel efficiency at lower speeds it is likely that more HARMFUL Carbon Monoxide might be released.

 

[torquil]

However, it could be argued that since cars have a lower fuel efficiency at lower speeds it is likely that more HARMFUL Carbon Monoxide might be released.

If I can drive the same car at either 100km/h or 80km/h on different gears at the same engine RPM, it's pretty obvious which speed is more efficient, even per unit distance. This happens because everything is approximately the same within the car, apart from the much larger air resistance...

I think that considerations about engine efficiency vs RPM (which shouldn't cause very much difference anyway since cars have gear boxes), are second order effects that cannot "compete" with the unavoidable increase in energy dissipation caused by the rapidly increasing air resistance as speed is increased (unfortunately, it increases more rapidly than v to the first power...)

There is no question that a car with a gear box and a combustion engine, if constructed to do so, will be more efficient (less energy loss per unit distance) e.g. at 80km/h than at 100km/h.

Unfortunately, as interesting as this discussion is, I guess it belongs in a different thread.