If you want to get it off to a good start, some formal senior management announcement would show it has senior support, plus usually most people pay attention when the 'boss' is presenting.
An important thing we lacked in our implementation was communicating the reason why we are doing it, what it means for the individual (both personally and corporately).
We had a few people trying to sell the 'saving the planet' line but it falls on deaf ears with most people unfortunately. When we associated activities to targets (e.g. sharing a car in saves money as well, bike scheme is good for health...) people soon started to see the value (and not just what they are getting out of it - but that was a nice sweetner to start).
Of course now we have gone full circle and as all staff see our senior management happily flying all over the place many feel less inclined to refrain from the drive into work.
Communication should include a timeline for implementation where possible. We launched a new IT system recently and many people who were enthusiastic at the start lost all interest and willingness to be involved when nothing happened for a couple of months and there was no update. That was a real negative.
Good luck
