Local Road Management Manual 442 maintain the condition of gravel roads at least cost to facilitate the passage of traffic in “all-weather” conditions. In achieving this objective, it is essential that the road surface is properly crowned ranging from 3%-5% from the centerline towards the side drains. Adequate drainage should be provided to rapidly collect and discharge surface water from the roadway. Recommended Average Daily Total Minimum Traffic (in both Thickness of directions) Sub-Grade Soil Classification Gravel (mm) A1, A2 , A3 Soils or if CBR > 7 150 A4, A5, A6, A7 Soils or if CBR is < 200 between 3 and 7 200 A1, A2 , A3 Soils or if CBR > 7 200 A4, A5, A6, A7 Soils or if CBR is > 200 between 3 and 7 250 Table 3. Pavement thickness for different CBR values Road drainage can be provided either through new drainage works where none already exists or through the repair and rehabilitation of existing drainage. New road drainage will generally comprise earth side drains. The use of masonry lined side drains will be minimized and specified only in exceptional circumstances. The use of concrete lined drains is not recommended. Existing cross-drains should, to the extent possible, be retained, repaired and rehabilitated. New cross drains may be installed where necessary, if none already exist or to increase existing capacity. In general new cross drains will be formed from RCPCs. The use of RCBC will be minimized and specified only in exceptional circumstances for technical and/or economic reasons. Existing headwalls, catch basins and outfalls should, to the extent possible, be retained, repaired and rehabilitated. New headwalls, catch basins and outfalls may be installed where necessary. Typical details for the RCPC cross drain with catch basin and headwall and for lined and unlined side drains are shown in Figure 4. Drainage works may extend beyond the limit of the road pavement rehabilitation works if this is necessary to make the drainage system