Do 20mph zones have a negative impact on the environment?

[J.H. Crawford]

>However, it made me wonder if a balnket speed of 20mph would be detrimental
>to the environment, does anybody know the answer or have any commnets about
>20mph zones?  

Part of the issue here is that cars are engineered to run well at high
speeds. The engines are far too large for slow speeds. I think most
cars get the highest fuel efficiency in the 40 MPH range, but that
will vary considerably from model to model.

Wind drag increases with the SQUARE of the speed (whereas rolling resistance
is roughly constant for a given distance). Total resistance is thus seen
to decline rapidly with falling speeds.

If cars were designed to run well at 20 MPH (with 5-10 HP engines), they
would use far, far less fuel than is now the case at that speed.



                                  ###

J.H. Crawford                                                 Carfree Cities
postmaster at carfree.com                                http://www.carfree.com