That's a load of bullshit
Not only is the average increase in fuel efficiency far below 100% but consumer cars are not the major use for foreign oil
and the number of vehicles that actually went through this program is pretty small compared to the number of older vehicles on the road.
And this is on top of the fact that with most of the people who participated in this program at the very least had to have the credit to buy a new car meaning the poorest people who drive the worst cars which have the worst mileage and worst emissions didn't get to participate. Not only that but those perfectly good cars could have been sold to a low income family that could use it to get a better job and bring their family out of relative poverty.
Oh and let's not forget all the fossil fuels used to transport the vehicles to the crusher, crush them, then transport the steel elsewhere. One of those trucks uses far more fuel than was saved by its entire load of clunkers.
Basically, this was one of the most inefficient, counterproductive and wasteful government programs in recent history.