Traffic Group Signals overcomes radio signal congestion


Responding to the challenging radio environment at temporary traffic signal sites, Traffic Group Signals has boosted the performance of its Active Channel Management (ACM).

The new ACM system allows the technology to overcome channel conflict by self-monitoring patterns using the 458MHz band over an extended period and automatically remembering which channels to avoid.

With the rise in radio usage for on-site communications, telemetry and automation, the frequencies in which temporary traffic signals operate are more congested than ever.

Congestion in the radio spectrum can result in the failure of traffic signal radio communications, cause significant disruption to road users and means regular call-outs for traffic management companies to restart the system.

Since upgrading the technology, Traffic Group Signals has experienced no instances of going to ‘lights out’ and experienced flawless communications between lights at one of the team’s most challenging sites in central London.

“The radio environment is challenging for temporary signals, particularly those situated in urban environments or close to construction sites/critical infrastructure,” says Darren Hudson, senior projects manager at Traffic Group Signals. “With a focus on making enhancements to address these challenges, we began to gather data to inform the changes to our ACM technology.

“Conventional temporary signals are unable to automatically adapt to congestion in radio bands, which can occur at random or persistently, for example, when walkie-talkies are used on construction sites. Instead, a laborious process of setting a new channel manually on each signal is required. This is time-consuming and typically leaves the junction unsignalled whilst the change is implemented. Even after such a change, there is no guarantee that the radio will operate reliably.

“While our existing ACM technology analysed the radio spectrum and adopted the channel most free of congestion, this may have resulted in changing to a channel that is quiet at night and busy during the day, which raised the risk of radio interference.

“The upgraded ACM radio technology takes more account of the bigger picture in terms of other users of the band that come and go with time. The result of this is that the system makes fewer channel changes but the choice of channel is exactly the one required to keep the system running at peak performance.

“This change in emphasis also helps the systems around us better decide which channel to use, allowing Metro and Evo1 signals to work in harmony with other frequency users.”

The latest enhancement to Traffic Group Signals’ ACM Technology is initially being rolled out across Metro Pro and Evo1 Pro enabled systems throughout 2023. For more information, please visit Active Channel Management Technology is patent pending.


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Tom has edited Traffic Technology International (TTi) magazine and its Traffic Technology Today website since May 2014. During his time at the title, he has interviewed some of the top transportation chiefs at public agencies around the world as well as CEOs of leading multinationals and ground-breaking start-ups. Tom's earlier career saw him working on some the UK's leading consumer magazine titles. He has a law degree from the London School of Economics (LSE).