[tialaramex]

Single Track means there is just one vehicle width shared both directions, if you meet someone coming the opposite way too bad, the next size up is Single Track with Passing Places (at intervals the road is wide enough for vehicles to pass in opposite directions). Not many Single Track A roads left in Britain, the A roads have mostly been upgraded even in Scotland. You're likely thinking of single Carriageway, which means there's only one road surface but it has separate lanes in each direction. Lots of those.