Discussion

P.W. TEETON, Sir Alexander Gibb& Partners. Reading I would like to refer to Transport and Road Research Laboratory Report No. 43, 'Theoretical average journey lengths in circular towns with various routeing systems', which was published in 1966. Twelve theoretical routeing systems were examined and six basic ones are reproduced in Fig. 1. I would also refer to the derived average theoretical journey lengths on each of the five basic routeing systems for three types of journey, namely:

internal cordon journeys cross-cordon journeys

and through (bypass) journeys (Table 1).

It will be seen from Table 1 that the longest average journey lengths for internal and cross-cordon journeys are given by the external ring system, while that for through journeys is given by the radial system. The shortest average journey lengths are given, apart from the direct system, by the external ring/radial system. The use of this system requires, however, traffic from some locations to pass through the centre of a circular town to achieve the theoretical minimum journey length. This routeing is often not feasible or practical due to congestion, and thus the next best practical alternatives will be sought. These are seen to be the internal ring and/or radial/arc systems, which are similar in concept and provide almost equal average journey lengths.