UK traffic lights kept failing for a year — then engineers found slugs in the controls

Safety worries grew after traffic lights at a busy crossroads in England kept failing for more than a year, creating confusion for drivers. The explanation was more unusual than a typical wiring fault or collision damage: slugs had made their way into the controls.

Here's what to know

Transport for Greater Manchester eventually linked the repeated outages at the Robin Hood crossroads in Stretford, Trafford, to slugs entering the signal controller and causing short circuits, as the BBC reported. That finding came after the signals kept failing despite multiple repairs and replacements.

Officials recorded three dangerous incidents over that period.

A TfGM letter stated, "With the exception of one outage caused by a road traffic collision, the faults shared the same underlying cause. Slugs had entered the signal controller and caused short circuits."

Councillor Steve Adshead said the pattern was especially hard to explain because the lights were still relatively new. "For them to go several times less than a couple of years old seemed very odd," he said.

More background

When traffic lights go out, drivers can miss right-of-way signals, pedestrians may be left unsure when it is safe to cross, and congestion can build quickly at an intersection that relies on clear direction.

Officials believed the slugs were crawling into the equipment for warmth and were then killed by the electrical system powering the lights.

Repeated failures also carry a financial cost. Repairs, replacements, inspections, and engineer callouts all take time and money, particularly when crews are searching for a cause they have not encountered before.

What's being done?

In July 2026, TfGM carried out remedial work after identifying the cause of the failures. Crews inspected the controller's door and base seals for gaps, sealed those openings, and added copper tape around the electrical components to keep slugs away from the most vulnerable parts of the system.

The letter said, "Since these works were completed, there have been no further signal outages at this location."

Adshead said, "We had a couple of residents raise it with us saying 'why do these lights keep going?'" and added, "I had to push Transport for Greater Manchester on it quite a bit."

Where can I learn more?

Slugs were at the center of this traffic-light mystery, and they're hardly the only small creatures to cause big problems, as these articles highlight. 

• In Finland, officials offered cash prizes to residents to help curb Spanish slugs.

• On the Isle of Man, a sudden population boom left wallabies damaging local land.

• In Michigan, officials warned that out-of-control creatures ran rampant as lanternflies spread countywide.

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