If a crown I would put timber pegs or steel bars at each side of the road at about 1.0m offset from the road edge. Note elevations have to be adjusted for this offset.
Then I would put 2 nails on each peg (or wrap tape on the bar). The upper nail at one side of the road corresponds with the lower nail on the otherside of the road. The elevations of the nails should be set so that a stringline pulled between the nails is set at 200mm above finished road level.
The spacing of the pegs depends on the stage of construction and accuracy required. So for excavation to formation then a spacing of 20m closing up to 10m for roadbase.
The other way for excavation to formation is longer pegs so that timber crossheads are set at about 1.2m above finished road level. Instead of a stringline the level is sighted between crossheads with a measuring stick between sighting points.
