Rotary interchange on National Route 3

Abstract

Paper presented at the 23rd Annual Southern African Transport Conference 12 - 15 July 2004 "Getting recognition for the importance of transport", CSIR International Convention Centre, Pretoria, South Africa. The paper describes the background, modelling, geometric design and performance of the reconfigured Armitage Road/Sanctuary Road interchange on the N3 in Pietermaritzburg. This reconfigured interchange is the first rotary type constructed on a National Route in South Africa. The development of the node surrounding the original half-diamond interchange (including a regional shopping centre), rendered the existing interchange incapable of handling the projected traffic volumes. The new interchange needed to satisfy both commuting and access requirements. Furthermore, the constrictions imposed by the site and financial constraints dictated that the options in meeting the stated goals were limited. In order to accommodate these divergent functions, innovative proposals were tested in the quest to provide an efficient and effective solution. The modeling and testing was undertaken using a combination of accepted computer programs namely SIDRA and the SimTraffic/Synchro pairing. The adopted rotary interchange was deemed the optimum in complying with the various constraints. This assessment process is described in detail in the paper. The rotary design parameters are dealt with covering, particularly, the geometry, the constraints and scope, roadmarking and signposting. The rotary was commissioned one week before the opening of the regional shopping centre that serves the entire KwaZulu-Natal Midlands. Consequently the rotary was subjected to intense testing in a very short period of time by motorists who themselves were undergoing a familiarization process. The performance in the weeks and months following the commissioning is explained in the paper covering the adjustments and fine-tuning necessary to achieve optimum performance and capacity.