Vehicle manufacturers opposed the measure. Many said it would be expensive to meet the standards (windows would have to block 45 percent of the sun's energy by 2014 and 60 percent by 2016). Jeep even went as far as saying the iconic Wrangler would go extinct because of the regulation. There was also talk at one point of making the paint on cars more heat reflective which lead to an internet rumor about the banning of black cars. Law enforcement opposed the measure because of the aforementioned ankle-bracelet-disappearing-ex-con problem and also because of fear that glazed windows would interrupt the cellphone reception of people trying to call 911.
Still, the idea behind "cool cars" was simple and elegant, though flawed; if car windows were better at keeping heat out, people would use AC less often. And if people used their cars' AC less often, they'd use less fuel and create less CO2. The estimates were that about 700,000 metric tons of CO2 would have been cut by the measure by 2020. Which is pretty cool.
[Source: Green Car Congress]