National Road Network Sinuosity Index

For each record (about 5,500 in total and each represents about 1 km of the network) the sinuosity is calculated. It is a ratio of the actual length over the Shortest path defined by the start and end nodes of the 1 km section. Section with a Sinuosity value of below 1.008 are considered straight and have a low driver demand. Sinuosity values greater than 1.031 are considered high demand roads. It has been put forward by Smith et al. (2006, 22nd ARRB conference proceedings) that drivers experience concentration difficulties on lower demand roads rather than high demand roads. In addition Sinuosity has been shown to be a good proxy for horizontal road bendiness. Road Bendiness is an essential imput into establishing alignment Constraint when calculating Design Speeds.