There were a couple of case studies at Velo-city 2010 from other cities which are colder andor hillier than Sheffield you might like to be aware of :-
Lausanne – 4% modal share
http://bit.ly/cS5TUf

Oulu, Finland – 20% modal share
http://www.ouka.fi/english/sports/cycling.htm

This session was packed out – I couldn’t get in the door!

All the presentations/abstracts from velo-city 2010 are now available at
http://www.velo-city2010.com/