A 2+1 road is a three-lane highway that has two travel lanes in one direction - one of which is used for passing maneuvers- and one lane in the opposite direction. The passing lane alternates every few miles. On some highways, traffic volumes are insufficient to justify a four-lane highway but are too great to be served by a two-lane configuration with permitted passing (when a vehicle can safely pass another) or a two-lane configuration which has occasional added-on passing lanes. In these conditions, a continuous passing lane whose directionality alternates is less stressful for drivers than finding a passing gap in oncoming traffic and minimizes the likelihood of head-on collisions with opposing vehicles. 2+1 roadways can be a good option in these situations.