Enterprise, National and Alamo are offering the largest carbon offset program in rental car history, which isn't saying that much. Eco-friendly persons who don't want to take the bus/train can opt to pay $1.25 on top of the cost of the rental (plus insurance, gas fees, et cetera) and the companies will match that amount up to $1 million in carbon offsetts. The plan will be administered by TerraPass, which is an industry leader in letting people buy their way out of their eco-guilt. No word yet on whether Hertz or other rental car companies will offer a similar plan, but it wouldn't surprise us. [Environmental Leader].