Operation of Traffic Signals during Low Demand Periods

It is not uncommon for criticisms to be made of highway authorities that the operation of traffic signals during periods of Low Demand (LD), for example overnight, causes unnecessary delays. In addition to building driver frustration, this leads to increased fuel consumption and the level of particulate emissions, resulting in an increased carbon footprint. Comparison is frequently made with practices overseas, where 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.

This study was commissioned to investigate, assess and recommend potential alternative techniques that could be applied at signal-controlled junctions in the UK during periods of LD.

The objectives of this desktop study are to investigate options for signal controlled installations that will help:
• Reduce unnecessary delays to traffic, hence minimising overall vehicle delays and emissions.
• Reduce the energy consumption of signal installations.
• Maintain or enhance levels of safety, especially for vulnerable road users.

Key conclusions
The study found potential options that achieve the first objective – “prevent unnecessary delays to traffic, hence minimising vehicle delays and emissions’. The design of traffic signal controlled junctions generally concentrates on periods of heavy demand, maximising capacities and providing facilities for all users of the junction. There is a tendency to assume that the same control strategy will suffice for all other periods, although this frequently imposes unnecessary delay on users,
increasing emissions and journey times as well as driver frustration. By careful study of individual installations or wider networks, it should be possible to minimise these non-peak delays whilst maintaining safe operation.