On high speed roads, head-on and loss of control crashes can occur when drivers try to overtake other vehicles. Overtaking lanes provide a safe opportunity for one direction of traffic to overtake and can improve traffic flow.
Traffic congestion, especially in developing countries, is recognized as a challenge. Building additional lanes to increase road capacity is costly, but lanes can be added to short lengths of road to improve traffic flow and provide safe opportunities for overtaking at less cost. If provided with regular safe opportunities for overtaking, drivers will be less likely to make dangerous overtaking attempts.
Overtaking lanes are generally used on high-speed arterial roads where there is a mixture of slow and faster moving traffic. In mountainous terrain some vehicles (especially heavy vehicles) will be limited to low speeds. An extra lane on steep descents (descending lanes) or up-hill sections (crawler or climbing lanes) can be used by other vehicles to pass safely.
Another option is slow vehicle turnout lanes. These are short sections of paved shoulder or added lane where slow vehicles can pull over safely and be overtaken. Slow vehicle turnouts may be more appropriate than overtaking lanes where traffic volumes are low or where an overtaking lane would be too costly.