The road centreline, or the grade line, will be marked during the set-out stage, and after the roadline trees have been cleared, the road centreline may need to be re-established. To effectively transfer the full road design information from the plan to the field, the grade line will need to be replaced with a centreline or use more sophisticated ways of providing guidance for the contractor. When a road has been designed using computer road design software, data is provided which enables the set-out to be installed by measuring off-sets from the original survey pegs. The format of this will vary depending on the software being used. The diagram below shows typical cross section outputs from RoadEng which indicate the position of the designed road relative to the survey station. Data sheets can be produced which provide offset slope distances for the batter pegs from the survey station. This is used to provide set-out for construction.
Initially, pegs are offset from the uphill side from the top of batter and offset from the downhill side from the toe of fill. This allows a contractor to remove the trees from the roadline. After the trees have been removed, the pegs are checked to ensure that they are still in place. The station number, and depth of cut (from the top of batter) or depth of fill (from the toe of fill), together with offset information is written on the peg. Reference stakes outside of the clearing limits may also be used. These provide a distance and bearing to the centreline.
Setting out a roadline
Source: Walbridge, 1997