BANGKOK, THAILAND – The city sped up its plan to replace fixed-time traffic lights with adaptive signals designed to ease congestion at major junctions.
Why Bangkok moved to accelerate upgrades
The Bangkok Metropolitan Administration (BMA) announced that it would accelerate the citywide rollout of adaptive traffic signals to relieve persistently heavy traffic. The move targeted the most important intersections, where outdated control systems still governed flows.
According to the administration, many main junctions continued to operate on a system that did not “see” the traffic, but simply ran through preset cycles. This approach left the road network unable to respond to changing volumes and patterns across the day.
746 major junctions, most still on fixed-time control
Out of 746 key intersections in Bangkok, more than 80% still ran on a fixed-time system, according to Deputy Governor Wisanu Subsompon. Under this method, green and red phases were set in advance and remained constant.
Signal timings stayed the same regardless of whether one direction was overloaded or almost empty. This often produced long queues in some lanes while others moved with little or no traffic.
How the adaptive system uses cameras and algorithms
The new system used CCTV cameras and image processing to detect traffic volumes in real time. The information was transmitted to control boxes installed at the junctions.
In these units, newly developed algorithms automatically calculated signal times and continuously adjusted the phases. The aim was to align green times more closely with actual demand on each approach.
Why fixed schedules failed in daily traffic
The old method did not react to rush hours, incidents or sudden fluctuations. In Bangkok, this was particularly problematic when traffic loads shifted quickly between side streets and main arteries.
By contrast, the adaptive system analysed factors including traffic density and the length of queues up to 150 metres before the junction. This data was used to distribute green times for each direction as efficiently as possible.
Less “green emptiness” and protection against blockages
One core problem with fixed-time lights, according to the BMA, was lost green time when no vehicles were present despite a green signal, while lines of cars built up elsewhere. This so-called “green emptiness” reduced the overall capacity of busy intersections.
In addition, complete standstill threatened when vehicles blocked the junction. To counter this, the adaptive system incorporated a function called Gridlock Protection, which cut the green phase immediately once the flow beyond the intersection broke down.
Expansion plan for the current fiscal year
For the current fiscal year, the BMA planned to install adaptive controls at an additional 50 intersections. The programme focused on speeding up the conversion of the most critical junctions.
Most of the city’s large intersections, however, still operated under the old mode. The administration intended the new installations to be a step toward a broader modernisation of traffic management across Bangkok.