Short note: reverse or tidal flow operation

Reverse (tidal) flow operation is a traffic management technique in which the number of lanes available to each direction is changed with the time of day, so that more lanes are given to the heavier direction at peak hours. It is used where the peak flow in one direction is much larger than in the other (for example inbound in the morning and outbound in the evening on a commuter corridor).

 Morning peak (to city):     Evening peak (from city):
  --> --> -->  (3 lanes)      --> (1 lane)
  <--          (1 lane)       <-- <-- <--  (3 lanes)

Conditions for use

• A directional split of about 65:35 or more in the peak period, and a road with at least three or four lanes.
• Roadside access and turning movements limited.

Methods of control

• Overhead lane-control signals (green arrow / red cross).
• Movable (zipper) barriers, cones or lane-markers placed by crews.
• Signs and markings; enforcement by Traffic Police.

Advantages: uses existing road width more efficiently, increases capacity in the peak direction without new construction, and is cheap compared with widening.

Disadvantages: safety risk of head-on conflict if drivers do not follow signals, cost of signals and staff, confusion of drivers, and difficulty in turning movements at junctions.