(One of the other things which pops out is how little difference Labour's promise of electric buses makes. Yes, its good. Yes, every little bit helps. But its simply not a credible policy for the scale of the problem).
Tinkering around, you can make decent savings by modestly decreasing the number of trips or trip length, or increasing car occupancy. But the core message is the thing we already know: the big savings come from increasing vehicle fuel efficiency and switching to electric vehicles. The clean car standard - which basicly means adopting EU regulations a decade late - gets us most of the way there by itself. Ditto mass uptake of EVs. Combined, they allow an almost 70% cut, which is the sort of thing that's necessary if we continue to allow farmers to shirk their responsibility and continue to pollute. So the policy problem is how to drive that. It looks like the clean car standard will happen next year, now Winston's handbrake has been removed. But if we really want to drive change in this area and push people hard into cleaner vehicles, we need feebates as well.