Subzero temperatures cause ice formation in George Massey tunnel in Richmond, British Columbia. A Canada Post truck driver has been seriously injured by falling ice. Company responsible for the maintenance of the tunnel says there is no further danger to the drivers.

I never heard such a case before. How can they be sure that it was a one off case?

https://www.mromagazine.com/2020/01/20/ice-falling-in-b-c-commuter-tunnel-sends-driver-to-hospital-in-serious-condition/