(2 part post):
Hey! You've spotted me, have you? ;-)
I work, on an occasional self-employed basis for a firm which specialises in traffic survey work. (I'm a regional supervisor). You'll see, from the list on their website, that they carry out lots of different types of surveys:
http://www.ctstraffic.co.uk/
Many of the surveys (particularly if my team are sat by the side of the road) are 'junction turning counts' where we'll be recording the movements at each junction, classified by vehicle type. For example.we might need to record whether a vehicle is a bicycle, car, taxi (if listed separately from cars), bus, light van, or heavy goods vehicle. We'll also record whether the vehicle turned left, turned right or went straight on.
Some of those traffic counts are for specific purposes. (e.g. a County Council's Highways Department might be considering replacing traffic lights with a roundabout). Others are simply at randomly chosen sites (within fixed criteria) for TRICS:
http://www.trics.org/