THE TWO AND A HALF LANE RURAL ROAD

Two major methods of improvement for two-lane rural highways are realignment to a higher design speed, and upgrading to a four-lane divided An intermediate alternative which is now receiving some attention is the systematic provision of short overtaking lanes along the two-lane road, in effect creating a two and a half lane road. Recent studies have indicated that overtaking lanes may offer substantial benefits in travel time, level of service and safety at comparatively very low costs. This paper uses traffic simulation to compare different options for rural improvement and to investigate the effects of each option on traffic speeds, bunching and travel times. Construction costs and expected accident reductions are also considered, in order to derive overall measures of the relative cost-effectiveness of each option. The results suggest that the two and a half lane road may be a practical and effective alternative to both realignment and duplication of two-lane roads, offering many of the benefits of these improvements at much lower costs. The selective stage construction of long duplication projects is also shown to have many of the advantages of overtaking lanes (a). The number of the covering abstract of the conference is TRIS No. 368448. (TRRL)