That depends on the road. Hill country with lots of bends, rises and falls will require a close spacing, say 10m. Flat open country with very few changes in grades and direction may be stretched up to 50m or more. Urban roads with kerb and channel may be 10m, 15m or 20m again depending on the grades, curves, features, etc.
So you need to assess the stretch of road to be surveyed and decide what will give a reasonable result.
If the road is properly supervised and monitored for grading during construction, as-builting is not required. During construction, the road should be constantly monitored and measured at each of the stations to ensure uniform grade, placement of materials and cut/fills. Once the final lift of ACP or the grade (in the case of rural) is acceptable, there is no need to as-built because the road has already been measured.
If the survey is a prelim., pre-design or pre-construction then I suggest every 15 or 30 metres for centreline and ditch profile and 50 to 100 metres for cross sections. I also suggest that topographical features and changes be included also.
