That all depends Nick; if they are a trench system as part of a strongpoint where machine guns, ammo crates, small artillery/pak anti tank guns are moved around within, then the trench is not too wide.
Have a look at the trenches in Windtalkers or the trenches within the German strongpoints on Omaha Beach in Saving Private Ryan and you will see those trenches are pretty wide too.
Also, some trenches served two purposes; for infantry to fight from and as vehicle/tank ditches to have small vehicles/tanks get hung up on............