I once came up behind, and followed for about 15 minutes, a semi-trailer which occupied the centre of the Bruce highway. It weaved erratically to and fro across the centreline, as if the driver was having difficulty staying on the road.
I wanted to overtake, because I thought I could then warn oncoming vehicles. I right-signalled, flashed my lights, and moved out as if to pass, but there was no sign that the truckie had seen me, and the truck continued wandering all over the place. I had my family on board and it would have been suicidal to persist, so eventually I slowed and watched the truck disappear into the distance - still taking up the whole road.
Fortunately, there were no oncoming vehicles while I was following the semi, probably because it all happened just after dawn, and on a quiet stretch of open road.
