A motorcyclist stopped next to the lorry, and the lorry couldn't turn left as it was ahead only.
It would appear that this is automatic and a buzzer also goes off in the drivers cab so he knows it is happening.
I presume it only happens when the truck is stopped and from what i have read (which isn't much as it's hard to find out information about this device) it appears to sound even if the truck isn't turning left.
Whilst it is a lie that the truck isn't turning left, i certainly believe that you shouldn't be going past a vehicle like this in stationary traffic unless you can a. see far enough ahead that you can make it there before the lorry starts moving, and that it won't turn shortly after it starts moving and b. there is plenty of space to move past it and escape onto the pavement if things to go tits up.