According to this recent article on Foxnews.com, the Cars Allowance Rebate System (CARS), also know as the "Cash for Clunkers" program, that was introduced by the government a few years ago has fallen quite short of its anticipated impact on the environment and to the economy. The program offered an amount from $3,500 - 4,500 off the price of a new car if it had a higher fuel economy than the owner's current car to be traded in.
The government spent nearly $3 billion on this initiative only to find that the results were far less significant than expected. Not only was the total emissions reduction not substantial, but the overall impact on the automotive industry and the economy as a whole was somewhat of a bust. Further analysis of the CARS initiative shows that many of the sales of new cars were simply pulled forward from a future date in which the sale would have been made anyway. So the demand curve for new cars would have shifted to the right in the short run, but then would have reverted back to the left in the long run which would have basically equaled the same net result without the program.
The article also discusses the impact of employment and job creation in the short-term, which according to the author, could have been realized through tax cuts to employers' and employees' payroll taxes. If anything, we can see that billion dollar initiatives don't always have the long-term impact that they're touted to have at the time of implementation.