Yeah but it will take years for this to happen, and just replacing the trucks is only part of the cost - you still need to build new infrastructure to either charge with electricity or fuel with hydrogen. But wait! There is more - you need to pay millions to get rid of all the old infrastructure like gas stations that cities have, with old fuel tanks, distributors etc. In the current economic climate, I don't see how most of the cities could afford to do all of this.