Always with the Canadian Open stuff. Settle down. No one is disparaging Oakmont or the US Open.
All the spectator stands are temporary so why can't a bridge be the same? Of course it can be.
Now that I've given it 5 minutes of thought, here's what I'd do. Instead of making the temporary bridge for spectators, make it for players only, so it would have to be close to where the two existing bridges are for player routing from 1-2 and 8-9. Makes it a cheaper, simple design. Easy to set up and easy to remove. Just like scaffolding. The hardest part would be getting a permit from the Pennsylvania Turnpike Commission but given the economic boost the US Open brings to the community it's doable, and there are more than a couple of Oakmont members that could put in a good word with the PTC. This would improve spectator flow through this bottleneck as you can make each of the permanent bridges one-way, in opposite directions. I'll let you run with this idea and successfully implement it for the US Open's next turn at Oakmont.