This Note gives guidance on geometric design and the setting of geometric design standards for single carriageway rural (inter-urban) roads in developing
countries. It is aimed at government officials who are responsible for formulating policy on geometric design
and at engineers who are responsible for preparing road designs. It will also be of interest to personnel in aid
agencies and consultancies who are responsible for the preparation and design of road projects. Many countries
will have existing standards different from those described in this guide. This should not preclude the use of the standards in this guide, although where good local cost and benefit information is available, some aspects may need to be reviewed. Geometric design is the process whereby the layout of the road in the terrain is designed to meet the
needs of the road users. The principal geometric features are the road cross-section and horizontal and vertical
alignment. The use of geometric design standards fulfills three inter-related objectives. Firstly, standards are
intended to provide minimum levels of safety and comfort for drivers by the provision of adequate sight distances, coefficients of friction and road space for vehicle manoeuvres; secondly, they provide the framework for economic design; and, thirdly, they ensure
a consistency of alignment. The design standards adopted must take into account the environmental road
conditions, traffic characteristics, and driver behaviour.

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