Shaw: Regulatory limits on pollution emissions from power plants should be set in terms of the long-term average emissions level rather than peak emissions levels. Levin: But short periods of high pollution emissions pose dangers to the environment. Your proposal is akin to enforcing the highway speed limit by measuring vehicles' average speed, including the time spent in traffic or at stoplights, rather than their peak speed. Based on the analogy in Levin's argument, time that a vehicle spends at a stoplight is analogous to time that a power plant ['emits pollutants at a very low level', 'operates at peak efficiency', 'emits no pollutants at all', 'emits pollutants at its peak level']