>>5485007 (Q PB)

>How do you repair a bridge without closing it down?

You only close down half a time. You repair the half on the right side while you leave the left side open.

Then you reopen the side that has been repaired and close the other side so you can repair it.

It takes longer than just closing the bridge entirely and detouring traffic around it… but sometimes there isn't really a reasonable detour alternative available… or it's too inconvenient to close the bridge.