Running out of road corridor? Consider tidal flow – it’s not just for the ocean!

Road corridors in urban areas are increasingly constrained. Tidal flow systems (or ‘reversible’ lanes) are a form of lane management systems that allows traffic to travel in alternate directions within a lane (depending on the time of day or traffic conditions).

Essentially, traffic flow during peak periods is improved by making an extra lane available for vehicles travelling along the direction of “peak traffic flow”.

The factors which need to be considered when designing and implementing a tidal flow system include  (but are not limited to) :

  • System safety (operator safety, road user safety and pedestrian safety);
  • Operational reliability (redundancies, fault/failure response and emergency management);
  • System integration (tidal flow switch interruptions, integration with existing systems, impacts to lane capacity and flexibility for future conditions);
  • Whole of life costs (capital costs, NPV); and
  • Program schedule (design and construction phases).

A typical tidal flow system will have several different components which may include one or a combination of the following:

  • Manual reversal system;
  • Movable medians;
  • Concrete barrier movable median;
  • Painted line marking;
  • In-Pavement Lighting (IPL);
  • Changeable Message Signs (CMS); and
  • Lane Usage Signs (LUS).

A summary of the various options available to enable tidal flow systems, are outlined in Table 1.

Table 1 – Typical tidal flow system solutions utilised in Australia

Options Description Example
Do Nothing

(Live with Traffic Jams!)

Candy Poles


Concrete Movable Barriers

In-Pavement Lighting

Depending on stakeholder requirements, alternative options not described above could include -(but not be limited to) :

  • Pavement flaps;
  • Different coloured linemarking;
  • High Occupancy Vehicle (HOV) lanes;
  • Reversible lane entry pavement markings;
  • Flashmax with LED warning light;
  • Fixed barrier reversible lanes; and
  • Congestion pricing.

JJ Ryan Consulting undertook the options analysis and design managed the design, procurement, installation/construction and commissioning of the tidal flow system along Military Road in Sydney’s north shore.

Check out this brief video from Transport for New South Wales on the successful implementation of upgraded/extended tidal flow here:


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