Traffic Flow Metering...By Instinct

"Flow metering" ensures that cars go through at just the right rate to prevent bottlenecks. With 280,000 vehicles a day, flow metering is critical on San Francisco's Bay Bridge - the busiest toll bridge in the world. Surveillance cameras, electronic message boards, sensors, and other gadgets are used to control the flow metering lights. But when high-tech fails, its a Caltrans employee who manually controls the flow metering lights that regulate traffic across San Francisco's Bay Bridge by instinct and experience.