Operation of Traffic Signals During Low Demand Period

Operation of Traffic Signals During Low Demand Period


S Phull, Department for Transport; P Harman, AECOM, UK


The Department for Transport commissioned a desktop study to investigate options for signal controlled installations to respond to periods of low demand


Traffic signal design is a science that has been developed through decades to a point where the maximum efficiency can be squeezed out of the most congested of junctions. Conflicting needs of all road users are measured, evaluated and optimised such that the ever-increasing and varying demands continue to be managed with ingenuity and certain degree of perfection.

But our networks are aren’t always busy. In many cases the very justification for signal control is based on a problem that may only exist certain periods of the day. Even the most congested networks have their quiet moment, yet, in a deserted city during early hours of the morning, signals still cycle in some cases for non-existent traffic. Any driver who ventures into this scenario may sit in frustration at a red light while the ‘intelligent’ control system optimises the signals for phantom conflicting demands.

Does the UK tend to over-control? In other countries various techniques are applied to ‘demote’ signalised junctions to priority mode of operation, for example the flashing amber on main road/flashing red on minor road employed in some States of the USA, or signals that simply turn off overnight as in parts of Europe. What would be the benefits and perils of reverting to priority control during low demand periods, and how could this be achieved within the UK’s legislative framework?

The Department for Transport commissioned a desktop study to investigate options for signal controlled installations that could
• reduce unnecessary delays to traffic, hence minimising overall vehicle delays and emissions;
• reduce the energy consumption of signal installations; and
• maintain or enhance levels of safety, especially for vulnerable road users.

The study reviewed current practice in the UK and overseas, developed an assessment technique to identify the types of installation that may be suitable for an alternative low-demand strategy during periods of low demand and in liaison with 12 Local Authorities devised 25 potential control strategy options to meet the objectives. These options were then modelled on a small hypothetical VISSIM network, enabling assessment on factors relating to economy, environment, safety, legislation and design, and classified according to their potential for implementation – short, medium or long term – depending upon factors such as required changes to legislation, technology or driver comprehension.

The findings were notable – the options offering most benefit during low demand periods were also the most difficult to implement. However there are opportunities for embracing developing technologies and making minor changes to installation parameters that could reduce installation and maintenance costs and improve the efficiency of LD methods of operation that retain signal control and its intrinsic safety compared with priority operation.


Association for European Transport