Speaking of California, this week's Energy Commission workshop on low rolling-resistance tires put on quite the self-congratulating party with tire makers, environmentalists and government bureaucrats drinking from the same punch bowl. This is from the press release: "If a third of Californians bought fuel-efficient tires, they could cut their gasoline use by 100 million gallons each year," noted California Energy Commissioner Jim Boyd. Presumably, that number isn't a per-person savings.
The press release neglected to mention anything about safety concerns with these tires. Low rolling resistance tires reap their fuel savings by reducing the tire's contact patch (the area of the tire that is in contact with the ground). With less contact, the tire skids and spins much more easily. Putting bicycle tires on your car would give you sensational gas mileage.
California has mandated that the Energy Commission come up with an energy rating system for tires (the EU already has such a system). The trouble with this type of stand-alone rating is that all tires entail tradeoffs of performance, fuel economy, safety and durability. You want better performance? You'll get a softer compound, which gives up some durability. You want better economy? You'll sacrifice safety. Californians could probably reap as much fuel savings if they'd simply make sure their tires were properly inflated.
Source: California Energy Commission
