Strauss-type bascule bridges use a system of counterweights, gears and motors to rotate the leaves of the bridge up and back. An operator situated in the control room on the side of the bridge controls the traffic gates and signals and all the mechanisms for raising and lowering the spans.
After the operator receives a request to open the bridge, they conduct a scan of the bridge to determine if there is traffic crossing the span. The operator announces over the loudspeakers that the bridge will be opening, and begins the sequence of steps to prepare the span. Red lights mounted on the pedestrian and vehicle traffic gates begin to flash to indicate that the gates will be closing shortly. A warning horn begins beeping and remains on during the entire process. Three-color traffic lights are used to stop vehicles from entering the lift span.
The operator next lowers the vehicle and pedestrian gates which will prevent traffic from entering the span. They then lower the gates on the exit lanes of the bridge. When all traffic is clear of the span, the operator opens the span locks to disconnect the two lift span leaves from each other. (The span locks keep the ends of the leaves from bouncing as traffic passes over them.)
Two 70 horsepower motors turn the reduction gears connected to shafts and gears. The bascule leaf rotates on the trunnions. The tremendous weight of the lift span is balanced by the concrete counterweights, located below the roadway of the bridge. Each counterweight on the Burnside Bridge weighs approximately 1,800 tons. Strauss type bascule bridges differ from their Chicago type cousins in that each counterweight hangs from two trunnions at the rear of the leaf truss. This allows the counterweight freedom of movement to remain almost vertical during the opening on the leaves.
Once the lift span leaf reaches the desired height, the operator stops the motors, applies the span brakes and waits until the river traffic has passed beneath the span. After the river traffic has cleared, the operator reverses the sequence and lowers the leaves down to their resting position. When both leaves are locked into position, the operator will raise the gates, turn off the horn and lights and allow street traffic to flow again. The average time for a span opening on the Burnside bridge is eight minutes, though this may seem longer to those waiting in their cars for the bridge to reopen.