The biggest number in the US government's new fuel economy rules isn't a gas mileage estimate. Instead, the Transportation Department says that automakers' technology costs will fall through 2031 under the new Corporate Average Fuel Economy Standards by $60.6 billion, and GM is the biggest winner of the lot.

        

By far the largest figure attached to any single automaker in the government's modeled reduction is $20.4 billion, yet General Motors isn't banking a check. The National Highway Traffic Safety Administration is comparing the estimated technology costs of complying with the new ruleset against the costs modeled under the previous regulatory path.