We rented a car in the UK to drive up to Scotland and around. The Motorways are huge and much like any interstate at home. We went to Balloch for the night, and the next day started up along Loch Lomond. Pretty quick stuff got real.
We would be cruising right along and then the traffic would brake on down to ~10 MPH.
It was two trucks, or Lorries as they say meeting on a narrow bridge. At each one of those bridges there was a scattering of mirror pieces along the road. The guardrails were high enough to get car mirrors and it was that narrow.
It was not technically a single lane bridge, but rather a talented two lane bridge.