Cars per hour is the number every express tunnel watches. It is easy to get — your controller counts it — and it goes up when you are busy. But on its own it can tell you that a slow hour was a good one.
Throughput counts what passed
Throughput is what actually went through the tunnel. If the line was short, it was low; if the line was long, it was high. That makes it mostly a measure of demand, not of how well the tunnel ran.
Capacity counts what could have
Capacity is the number of cars the conveyor could have carried in the same hour if every slot on it had been filled. The gap between capacity and throughput, during the hours you had a line, is lost throughput: empty stretches of track that went through the brushes with nothing on them.
Where the gap comes from
- Loading gaps: the attendant waits for the car in front to clear before waving the next one on, leaving space on the conveyor.
- Stops: the tunnel halts for a stuck car, a misaligned wheel or an equipment fault, and the queue grows behind it.
- Slow entry: plate reads, plan sales and payment at the pay station meter cars into the tunnel more slowly than it can take them.
- Slow exits: cars that hesitate at the exit hold up the line behind them.
A controller sees none of these separately. It counts cars. To separate them you need to time each car from entry to exit, and the empty track between cars as well.
Measuring it
BayCam times every pass from the moment the car is read at the entry to the moment it clears the exit, using the cameras already watching the tunnel. Because it measures the conveyor as a whole, an empty stretch counts against you the same way a stop does — and the report says which one it was.
Throughput tells you how busy you were. Capacity tells you how much of that business you could have handled.
