Driving a hybrid is not environmentally responsible when:

*You had to sell a perfectly fine working vehicle to get the hybrid. There's a break-even point eventually where owning the hybrid makes up for the energy put into the manufacture and assembly of the hybrid from raw materials; but with a paid-for, working car, even a non-hybrid, you've already 'amortized' the environmental costs up front; it's more efficient to just keep driving the old klunker, up to the point where the hybrid's operating efficiency overcomes its environmental manufacturing load.

*You have an option to take mass-transit.

*You have an option to commute by bicycle.

*You have an option to walk.

*You have an option to carpool.

*In general, you shouldn't drive a hybrid if you have an option of using another form of transportation whose net environmental and energy footprint, from cradle to grave, is less than the hybrid's. Of course, this is also true when pondering the decision of buying any kind of vehicle, hybrid or non; it's more environmentally efficient to buy used, or keep the old klunker running.

~Joe

1998 VW Jetti TDI owner

Given the Yukon/Tahoe would otherwise only get ~15 MPG, getting 20 MPG is a significant improvement. Also, I suspect those vehicles could get even more if some of our 'lessons learned' were applied to them. For example, if someone doesn't need a heavy payload and off-road capability but is really transporting stuff around city or highways, lower rolling resistance tires running at semi-trailer pressures (aka., max sidewall) would really help them on the road.

I also think GM is at the low part of the "learning curve" with these hybrids (bus experience not withstanding.) If they follow the usual practice, in 2-3 years, they will make a 'step improvement' and probably bring these trucks up to 22-23 MPG. The key is whether they will recognize that the solution to low MPG is LOW DRAG and full-capacity, regenerative braking.

When I was in school learning the basic engineering math and physics, I remember learning that the energy expended to increase momentum, if efficiently captured, can be applied back to bring the object to the original velocity. The perfect example is a pendulum in a vacuum with a perfect pivot. Once started, the mass reaches a maximum velocity at the lowest altitude and then slows down as it climbs up. Another example is a planet in an elliptical orbit that constantly converts kinetic to potential and back to kinetic energy.

If GM can solve the drag and regenerative braking efficiency problem (this is not a trivial nor impossible problem,) they can convert their trucks into huge beasties that sip the smallest amounts of gas. All it takes is attention to the energy equations and then some clever engineering. It does not require 'unobtainium'.

These trucks are Version 1.00 (IMHO, possibly beta 0.95,) so we won't know for a couple of years if GM is able to sustain this technology. I hope they do but it isn't my call. I just wish them the best of luck!

Oh, as for the 600h, there are many fine reasons for having a hybrid that have nothing to do with saving gas. The complete and utter lack of vibration and incredible, low-end torque alone justifies a performance car using a hybrid drive system. That the 600h does not get better mileage really reflects upon DRAG and the challenge of regenerative braking.

Bob Wilson

ps. The only concern I have with the two-mode transmission is the relatively large number of parts. But I excuse this as what happens in many first generation technologies. You have to start with what you know and then you can simplify and improve. Heck, the first generation Prius, the NHW10, had many more parts than the NHW11 and the NHW20 has trimed the parts count again. It takes operational experience to give the insights to how to achieve an efficient design . . . the school of hard knocks.

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Hybrids are not environmentally responsible when they offer no greater mpg or range than their ICE counterpart - i.e. the GM hybrid truck that is currently advertised.

I rented one of the first Toyota Prius' just to see what it was all about, and I was very impressed. The first gen Prius had everything I needed, and a few things I had never thought of to ask. I ran it flat out on the California freeways and hit 110mph before I decided to back out of it. Twice the legal speed limit in the only state it was designed for, and dead quiet - not to mention safe. Not bad for a first generation vehicle, and then they had to up the size of the engine - why? This car returned 41mpg average in the fashion that I was flogging it - had I merely driven it in the way it was intended I would've certainly hit the 50mpg mark.

The hybrid mark has been made a badge of the environmentally conscious, and yet - as we have seen - they are not always designed for this purpose. Kind of like carrots made into missiles, this badge can be misconstrued.

There are so many things that we should do to improve the way we operate. The problems abound because we do not apply the technology we have at our disposal. Commuter cars are a good idea, but way below the radar in terms of making a difference.

We are not breaking ground with hybrid power, the railroad industry did all of this and more at least 35 years ago with the beginning of the diesel-electric locomotives (which is the standard today).