Expected degree of use

In remote, lightly used locations the lower wear and tear expected will favour unsealed surfaces; the converse will apply at popular, heavily used areas. This also applies at short – stay facilities, where the turnover of visitors means that the surfaces are likely to be heavily used by vehicles.


If the ROS is being followed then the remoter, wilder areas will favour unsealed surfaces, whereas in the more urban settings sealed finishes will be more acceptable. It may also be appropriate to use unsealed surfaces near urban areas to emphasize the more relaxed, rural or wild setting and atmosphere being created.


Surfacing must include proper attention to drainage. Sealed surfaces produce more run­off, which has to be channelled away. Expensive pipe drains can be entertained only on large developments. Laying the surface to gradients allowing run-off into french drains (rubble-filled ditches), into open ditches or over the surface of nearby areas may be acceptable instead. Care must be taken to avoid drainage water flowing directly into streams, as the silt and pollutants (oil, fuel, and exhaust particles) could be harmful to aquatic life.

Expected degree of use

Diagram showing how snow storage can be designed into the car park layout together with the meltwater drainage.

Unsealed surfaces also need to be kept drained, although water may percolate through them to a greater degree. Good gradients across the area are needed, but areas to be drained should be broken into sections to avoid the danger of erosion, particularly during heavy rainstorms. Unsealed surfaces can be prone to washout. Excess water in the structure of the road weakens it and can make it more prone to structural failure under heavy loads such as fully laden coaches.