An assessment was made as to whether the European 2+1 road design is suitable for use in the United States. A 2+1 road design has a continuous three-lane cross section with alternating passing lanes. This digest describes when a 2+1 design is likely to be effective and presents some recommendations for designing 2+1 roads. Visits were made to Germany, Finland, and Sweden to meet with agency staff, observe 2+1 roads in operation, and obtain data on their traffic operational and safety performance. Because of European experience, the use of 2+1 roads in the United States is recommended. It has been found that 2+1 roads improve the traffic operational level of service for two-lane roads without increasing their capacity. A 2+1 road will generally operate at least two levels of service higher than a conventional two-lane highway serving the same traffic volume. Also, a 2+1 road can operate safely and effectively in areas where minor intersections and driveways provide direct access to the roadway. Major intersections should generally be located in the buffer areas between passing lanes in opposing directions of travel and should have left-turn lanes provided. While 2+1 roads can operate effectively with no separation between the lanes in opposite directions of travel, AASHTO policy states that some separation, however small, between the lanes in opposite directions of travel is desirable. Therefore, a flush separation of 1.2 m (4 ft) between the opposing directions of travel should be considered, where practical. Sweden uses a cable barrier in a flush divider, Finland is considering their use, and Germany considers their use undesirable. It is recommended that use of cable barriers between the opposing lanes of 2+1 roads not be considered in the United States until a full evaluation of tort liability and barrier deflection issues has been completed. (Author/publisher) This report may be accessed by Internet users at http://trb.org/publications/nchrp/nchrp_rrd_275.pdf
Abstract