2 + 1 Highways: Overview and Future Directions

Abstract

Most of the rural transportation system is composed of two-lane highways, and many of them serve as the primary means for rural access to urban areas and freeways. In some highways, traffic volumes can be not high enough to justify a four-lane highway but higher than can be served by isolated passing lanes, or can present high number of head-on collisions. In those conditions, 2 + 1 highways are potentially applicable. This type of highway is used to provide high-performance highways as intermediate solution between the common two-lane highway and the freeway. Successful experiences reported in Germany, Sweden, Finland, Poland, or Texas (US) may suggest that they are potentially applicable in other countries. The objective of this white paper is to provide an overview of the past practice in 2 + 1 highways and discuss the research directions and challenges in this field, specially focusing on, but not limited to, operational research in association with the activities of the Subcommittee on Two-Lane Highways (AHB40 2.2) of the Transportation Research Board. The significance of this paper is twofold: (1) it provides wider coverage of past 2 + 1 highways design and evaluation, and (2) it discusses future directions of this field.

Detection of Geometric Risk Factors Affecting Head-On Collisions through Multiple Logistic Regression: Improving Two-Way Rural Road Design via 2+1 Road Adaptation

“…There are several studies in the literature dealing with head-on crashes on rural roads and also some considering the characteristics of "2+1" roads and how these help to reduce crashes. However, many of these studies are not inferential as the one performed here, but descriptive [8,9,[25][26][27][28], so no statistical inference can be obtained, i.e., their results should not be extrapolated. Among the inferential studies, some of them consider all types of crashes [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], which is not convenient to our purpose, as we are studying the crashes that can be avoided by "2+1" road transformation.…”

“…One way of preventing head-on crashes on “1+1” rural roads is to transform them into “2+1” roads and avoid dangerous overtaking without harming the volume of traffic. These “2+1” roads are receiving increasing attention in the literature and there are some interesting studies concerning their characteristics, the volume of traffic they may support and how the overtaking sections should be designed [ 13 , 14 , 25 , 26 , 27 , 28 ].…”

“…2+1 roads [25][26][27][28] Descriptive 2+1 roads are effective in the following situations: For higher-volumes or in areas where minor intersections and driveways provide direct access to the roadway. Also, in mountainous terrain with long, steep grades.…”

“…Some of these contributions come from descriptive studies [ 8 , 9 ], while others come from inferential ones, using different models and schemes [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. However, there are not so many results concerning “2+1” roads and they are mainly descriptive [ 25 , 26 , 27 , 28 ]. See also Table 1 for the main results obtained in these studies.…”

Safety and Mobility Performance Comparison of Two-Plus-One and Two-Lane Two-Way Roads: A Simulation Study

“…A passinglane length of less than 1000 meters is not recommended [9,10]. Internationally, the passing-lane length is between 800 to 3500 meters [11]. Durth (1995) recommended that passing-lane section lengths between 1000 and 1400 meters for volumes of up to 1000 vehicles per hour per direction, with heavy vehicles (HVs) percentages of up to 15% [12].…”