Chevy Corvette 4-speed automatic
----------------------------------
power = 400 horsepower
weight = 3199 pounds
p/w ratio = 0.125
acceleration (0-60 mph) = 4.42 seconds
fuel economy (city/hwy) = 18/26 miles per gallon
seating capacity = 2
cost = $50,000 U.S.

Ford Focus 4-speed automatic
-----------------------------------
power = 136 horsepower
weight = 2654 pounds
p/w ratio = 0.051
acceleration (0-60 mph) = 8.9 seconds
fuel economy (city/hwy) = 25/32 miles per gallon
seating capacity = 4
cost = $15,000 U.S.

Analysis
------------
1. Dividing the p/w ratio of the Corvette by the p/w ratio of the Focus suggests the Focus should take 2.45-times longer, or 10.8 seconds, to accelerate from 0-60 mph. It actually does it in 8.9 seconds, a bit better than expected.

2. Dividing the weight of the Corvette by the weight of the Focus suggests that the Focus should get 1.2-times better fuel economy, or 21/31 city/hwy. This estimate is very close, in fact it does significantly better in the city.

3. The Ford Focus also has double the seating capacity for 30-percent of the price of a Corvette.

Conclusion
--------------
My idea that regulatory caps on vehicle weight and horsepower for non-freight vehicles as a means to halt growth and eventually reduce per-capita fuel consumption and dependence on foreign oil appears to be approximately supported by vehicle performance specifications. This was expected from kinematics "first principles" found in any introductory high-school-level physics textbook. Since greenhouse gas emissions are directly related to the quantity of fuel consumed, these regulatory caps should also be expected to prevent growth of emissions, and provide a mechanism to reduce them in the future.

Note - this is not an endorsement of any particular brand or model of car, merely a trivial demonstration of the power of mathematics.