Tradeoffs Between a 2+1 Lane Road Design and a Narrow 2+2 Lane Road Design
Lars Hissingby Trandem, Norwegian University of Science and Technology, Kelly Pitera, Norwegian University of Science and Technology
This paper will look at the tradeoffs between a 2+1 lane road design and a narrow 2+2 lane road design, considering traffic safety, capacity and level of service, costs, and non-monetized impacts.
Abstract - European Transport Conference 2016
Title: Tradeoffs between a 2+1 lane road design and a narrow 2+2 lane road design
Short summary of the abstract: This paper will look at the tradeoffs between a 2+1 lane road design and a narrow 2+2 lane road design, considering traffic safety, capacity and level of service, costs, and non-monetized impacts. Additionally, a case study examining a 2+2 road configuration within Norway will be discussed.
In Norway, a new, alternative road design consisting of a 16 to 16,5 meter wide cross-section in a 2+2 configuration is being considered to see if it could be an acceptable and feasible solution compared to the more common 2+1 lane road design configuration. Currently the narrow 2+2 lane road is in a trial phase in Norway and not a part of the Norwegian Road Administration’s standards for road and street design.
The cross section of the 2+1 lane road design consists of in total three lanes, two lanes in one direction and one lane in the opposite direction, divided by a median barrier. The direction of the middle lane is alternating giving both directions, at regular intervals, the advantage of a passing lane. This design is normally used in rural areas with mid-range traffic volumes to prevent head-on accidents and thereby increase the safety of a standard two-lane road.
There is interest in examining if you can achieve the same positive effect regarding traffic safety, and also increase the capacity and level of service of the road by building a narrow 2+2 lane road, with minimal increase in construction costs. This solution is suggested for road sections where the annual average daily traffic is not high enough to justify the costs of building a normal four-lane road. It is assumed that the costs of upgrading the 2+1 lane road into a four-lane road at a later stage, when a greater capacity is required, would be more expensive than building a narrow 2+2 lane road in the first place. Thus, the narrow 2+2 lane road is a compromise between a 2+1 lane road and a standard width four-lane road and it is important to explore further the tradeoffs between such cross-section designs.
In addition to the safety, costs and traffic operations aspects of the different road designs, the non-monetized impacts like landscape, local surroundings and outdoor activities, biodiversity, cultural heritage and natural resources should also be considered, as is standard in Norwegian consequence analysis methodology. The expectations regarding the non-monetized impacts are that there will be minor differences between the 2+1 lane road design and the narrow 2+2 lane road. The non-monetized impacts seem to be more dependent on the local surroundings and the actual construction of the road, rather than the difference in road design when the variation in the cross sections is so small. These aspects will be discussed in the trade-off analysis and can provide information to the decision makers for future road projects.
The aim of this paper will be to look at the tradeoffs between the narrow 2+2 lane road design and the 2+1 lane road design, by looking into characteristics like design, traffic safety, capacity and level of service, costs, and non-monetized impacts.
The study will be done by examining existing research and literature for comparative roadway designs regarding traffic safety, capacity and level of service, costs, and non-monetized impacts. This literature study will be used to conduct a trade-off analysis, highlighting positive and negative aspects for both design solutions. A case study of a project in Norway where a narrow 2+2 lane road configuration has been used will also be examined using current Norwegian alternative assessment tools.
This research will be done during the spring 2016. Based on the study the tradeoffs between the narrow 2+2 lane road and the 2+1 lane road, recommendations for the use of such road configurations will be given. The results of the Norwegian case study will also be presented, and the two parts will be linked together and discussed to draw conclusions on the use of a narrow 2+2 lane road design.
Association for European Transport