Although I generally support initiatives to reduce energy use, I think this
proposal would be a mistake.

First, it will take some years before hybrid production can be ramped up to
meet the demand this would cause.
Second, fleets have different needs.  Not all kinds of vehicles will be
available in hybrid styles for some years.  This will lead, inevitably, to
unfair application of the law of a maze of special exemptions that will make
the initiative meaningless.
Third, why anoint hybrid technology this way?  Why not just set fleet mpg
targets and let the other market forces sort out how to achieve them?

I'd just as soon see the gas tax raised to something punitive and made
deductible.  Or a per barrel tax (Krugman described this) that sets a floor
for oil prices and raises automatically with the spot price.

We don't make very good choices in transportation and energy policy.  Around
here, we've blown close to a billion bucks on a single Light Rail Transit
line.  It uses up valuable street space, has frequent accidents with
passenger vehicles and, in spite of the nearly-a-billion bucks spent, I can
neither get to work (3 miles) by public transportation in less than 1.5
hours, nor can lower-income people come to my inner-ring suburb by public
transportation to take jobs.  But LRT is sexy, so that's what we get.

How many hybrid busses could we buy for a billion dollars?