2+1 road (also written as "2-1 road" in a different configuration) is a term used in transportation engineering to describe a specific type of road layout.
There are two distinct concepts that the notation "2 1 road" can refer to:
1. 2+1 road — A three-lane road with two lanes in one direction and one lane in the other, alternating every few kilometres. The second lane allows faster-moving traffic to overtake slower vehicles at regular intervals. These roads are often separated with a steel cable barrier or pavement markings. This design is common in Sweden, Germany, Finland, Denmark, and increasingly in the United States (where it is sometimes called a "Super 2" highway). Crash data from Sweden shows that 2+1 roads with cable barriers reduced fatal and injury crashes by approximately 55–80% compared to conventional two-lane highways.
2. 2-1 road (2-minus-1 road) — A different type of road with extra wide shoulders and a smaller single two-way lane in the middle for vehicles. The shoulders are used by pedestrians and cyclists, and if necessary by meeting vehicles. This design is popular in Denmark and Sweden (where it is called bymiljöväg, or "village environment road") and is intended to give more space to pedestrians and cyclists without constructing dedicated bicycle paths.
The term "2 1 road" without a plus or minus sign is not a standard established term in transportation engineering. It is most likely an informal or shorthand reference to either a 2+1 road or a 2-1 road, depending on context. In the UK road classification system used by road enthusiasts, "S2+1" denotes a single carriageway road with three lanes where one direction takes two lanes and the other takes one.
