Shaw argues that limits on pollution levels should be based on average emissions rather than the highest peaks. Levin disagrees, arguing that basing the regulatory limit on averages would be akin to basing speed limits on cars’ average speeds, which wouldn’t make sense given that such an average would include times when cars are slowed by traffic or stopped at red lights.

The question asks us to find what, for a power plant, would be analogous to times when a car is at a red light. Cars’ average speeds are likened to a power plants’ average emissions, and cars are not moving at all when they’re at a stoplight, so such time would be analogous to times when a power plant does not emit any pollution at all.