Tidal flow operation methods

 TIDAL FLOW OPERATION METHODS

Tidal flow operation is a traffic management process whereby the carriageway width is shared between the two directions of travel in near proportion to the flow in each direction.

• The objective of Tidal flow operation is to provide a cost-effective means of increasing the capacity of a road.
• Tidal flow refers to a road where a lane or lanes can sometimes carry traffic in one direction and at other times in the opposite direction, to help with traffic flow. 
• Traffic signals usually indicate when a lane is open or closed.
• Tidal Flow is also sometimes installed in tunnels or bridges, to allow traffic to be diverted around
• Tidal Flow tends to be used on roads where the flow of traffic is heavy in a certain direction and light in the other at some times, and then reverses at other times.
• Overhead signals will show either a white or green downward arrow when a lane is open and a red cross when a lane is closed.
• The term "Tidal flow" is used in British English while other parts of the world, the term 'reversible lane' is used.
• The benefit of tidal flow (reversible lanes) operation is that the available capacity in each direction of traffic can be varied in response to highly directional inbound or outbound traffic flows.
• An odd number of lanes, usually three to seven, is required for effective tidal flow operation.
• The middle lane operates as a contraflow buffer zone to serve traffic in different directions
• To ensure safe operation of contraflow, lane-use control signals with green arrows and red intersections located at overhead gantries are used wherever a particular movement is prohibited for designated lanes.
• Examples of sites that employ tidal flow operations are
• Aston Expressway (Birmingham, UK)
• Canwick Road (Lincoln, UK)
• London Road (Sheeld, UK)
• Wide boulevards and some freeways in Washington, D.C. (US)
• Coronado Bridge (San Diego, US)
• Tidal Busway (Eugene Oregon, US) 
• Several urban roads in Rio de Janeiro and Sao Paulo (Brazil), part of State Road SC-405 (Florianopolis, Brazil).
  

Advantages 

1. Increase in motorway capacity during peak traffic hour at relatively low cost to governmental organisations
2. Cost of these tidal flow lanes is a fraction of the cost to construct additional motorway lanes 
3. Minimum disruption to traffic
4. Reduction in congestion
5. Safety benefits

Disadvantages 

1. A major disadvantage is is the cost to efficiently control reversible lanes and the confusion to drivers and safety.
2. A disadvantage of reversible flow lanes involves general lack of public awareness. 
3. Traffic flow is potentially confusing
4. Complication of nearby signals