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

[Kerry Wood]

Broadly speaking, no.

One figure I have seen is a range, from a10% fuel saving to a 5% fuel increase,
depending on driving technique (aggressive second gear or relaxed third gear).
This suggests that closely spaced traffic calming features will make aggressive
driving pointless and so reduce fuel use.

Road planners use curves of speed against fuel consumption, to calculate the
effect of their roading schemes. (I have seen one of these that assumed a
continuously falling curve: LESS fuel use at 200 km/h than at 50 km/h!) All
these curves contain the assumption that speeds of less that 50 km/h (maybe
more?) are due to stop-start driving in congested traffic, and so the curves are
not applicable to slow and steady driving in traffic calmed streets.

And of course noise and crashes are environment too.

Regards

--
Kerry Wood  MICE  MIPENZ  MCIT
Transport Consultant
1 McFarlane Street, Wellington 6001, New Zealand
Phone + 64  4  971 5549