FEASIBILITY OF 2+1 ROADS ON ALBERTA RURAL HIGHWAY NETWORK

Background Over the last twenty years, European countries have built several thousand kilometres of “2+1 roads”, in which an existing or new 13 to 14 metre wide, paved two-lane road segment (8 to 20 kilometres long) is re-striped into three traffic lanes, with the centre lane used as the passing lane in alternate directions. The European 2+1 roads serve traffic volumes from 6,000 AADT to 30,000 AADT. Many are quasi-freeways with grade separated access. At-grade intersections are discouraged; where they cannot be avoided, they are, as a rule, placed in the transition zone between adjacent alternating passing lanes. From the European experience, it is evident that the 2+1 road design aids in the economic, environmental and social sustainability of roads, because it: (a) reduces fuel consumption by improving the road’s Level of Service by reducing platooning and congestion; (b) helps defer or avoid the need for road twinning; and (c) reduces the rate of fatal and serious injury collisions by an average 25 percent. Objective of the Study The European 2+1 road design has not yet been implemented in North America. The objective of the study reported in this paper was to assess the feasibility of implementing the European 2+1 road concept on the rural Alberta highway network managed by Alberta Transportation (AT), and if found feasible, to propose a small number of segments for implementation. Methodology As a first step, an exhaustive literature search was conducted to gain insights regarding the European 2+1 road design standards and criteria, and improvements achieved in safety and Level of Service. AT’s warrants and criteria for twinning and climbing/passing lanes were reviewed, as well as the access control and geometric standards and guidelines. A short list of 12 Control Sections (from an initial long list of 67 Control Sections on the Alberta two-lane rural highway network) was developed for potential 2+1 road application on the basis of the following factors: traffic volumes, collision rates, and AT’s warrants and planned programs for twinning and for climbing/passing lanes. All of the 12 Control Sections were “virtually driven” using AT’s digital video log. The purpose was to note the location and number of major and minor intersections, and other features such as bridges that could influence the suitability of the 2+1 road design. In the 12 Control Sections it was possible to identify 15 potential 2+1 road segments ranging in length from 7 to 24 km. Unfortunately, however, it turned out that the potential segments contained an average of 2.7 intersections per km, with a range of 0.8 to 4.1. Conclusions 1. The European 2+1 roads concept does not appear to be suitable for general application on the Alberta rural highway network, because: ƒ It would be very difficult to accommodate the large number of intersections in the 2+1 road design because of Alberta’s requirements for safety performance and sight distance. Even if it were possible to accommodate these fixed-location intersections in the transition zone between adjacent passing lanes, adequate sight distances at these transition areas may not be available. In addition, the frequent presence of intersections within the 2+1 segments would increase the likelihood of collisions, thus potentially negating a main benefit of 2+1 roads. - 2 - ƒ On the European 2+1 roads, improvements of two Levels of Service (e.g., from D to B) have been experienced. On Alberta rural highways where the Level of Service is frequently “A”, it will be impossible to achieve a significant improvement in Level of Service through conversion to the 2+1 road configuration. The existing “net passing opportunity” requirement as defined in Alberta’s Geometric Design Guide is relatively high, and the conversion to 2+1 configuration would result in large transition areas that must be marked as “no passing” in both directions. It is therefore unlikely that the “net passing opportunity” could be improved on Alberta rural highways by the 2+1 design. 2. The European 2+1 roads concept may be more feasible elsewhere in Canada: for example in Nova Scotia, where some sections of arterial two-lane highways are quasi-freeways with gradeseparated access control.