Rule #1 of efficiency improvement: Improve the low efficiency items first. There is more to be gained by bringing a low-efficiency item up slightly than there is in bringing a high-efficiency item up significantly.
This is why I piss off the greenies quite often when I talk about making trucks and SUVs hybrids first makes sense. Noooo... They want them to give UP functionality first.
Talked with a UPS guy yesterday, as a matter of fact. I mentioned that I had read about them buying hybrid trucks - he said that they're going in everywhere, but that our area (ND), would be getting them last. To the point that they're sending the old non-hybrids to us.
My conclusions:
1. Hybrids make sense for UPS
2. Hybrids make more sense in more southern areas, especially where gas prices are higher
3. It doesn't make sense, yet, to replace trucks faster than attrition.
Other candidates that I'll let buy hybrids first: Taxis, inner city drivers, etc...