Academics in the US have assessed whether drivers understand cyclists’ communication cues, and looked at the effectiveness of arm signals, head movements, eye contact and road positioning in helping people on bicycles to inform other road users about their intentions.

Arm signals were the most effective form of communication, according to the researchers, who also noted, in news that will surprise few, simulating a mobile phone conversation saw drivers’ accuracy in interpreting cyclists’ signals reduce, something the study concluded “highlighted the dangers of distracted driving”.

One of the study’s authors, Rice University academic Christine Petersen, explained to Medical Xpress that the clearest form of communication was through clear, arm signals, such as holding your arm out straight in the direction a cyclist wishes to turn.

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“Signals that match the direction of movement, pointing where you’re going, are especially important for keeping interactions predictable and safe,” Petersen said. “Hand signals matter, but clarity matters even more.”

The study saw 60 drivers watch video clips of a cyclist performing combinations of different cues, for example head movements, arm signals and utilisation of different positions on the road.

Riding hand signals - turning.jpg
Riding hand signals – turning.jpg (Image Credit: Farrelly Atkinson)

Drivers then expressed what they believed the cyclist’s intended manoeuvre was based on the signal and the researchers collated the results to assess levels of accuracy for different cues.

While the drivers predicted cyclists’ intentions with “above-chance accuracy”, it was only arm signals which “significantly” influenced correct predictions. “Head movement and position on the road had no significant effect,” the study stated.

A post-study questionnaire delved deeper into what the motorists understood of the signals used.

Cyclist hand signal
Cyclist hand signal (Image Credit: Farrelly Atkinson)

“In the United States, cyclists are required by law to use arm signals to let other road users know they intend to turn or stop (Transportation Code, 1995). To indicate their intentions to turn left, the cyclist is required to extend their left arm straight out. For a right turn, the cyclist can either extend their right arm straight out or bend their left arm at a 90-degree angle and point it upward. To signal slowing down and/or stopping, the cyclist must bend their left arm downward at a 90-degree angle,” the researchers explained.

The questionnaire data found that while all drivers correctly defined straight-arm turn signals, the bent-arm signals were less well known, with less than a quarter of participants understanding them.

The study concluded: “These findings suggest that cyclists should use straight-arm signals and consider adapting the stop/slowing signal to better align with drivers’ expectations. Using communication cues that match drivers’ mental models may reduce confusion, improve situational awareness, and help prevent collisions—especially when driver attention is compromised.”

To simulate distraction, the researchers had some participants complete their task while simulating a phone call. While this was just talking as if on the phone, not using a mobile phone ‘behind the wheel’, the researchers reported a notable drop in accuracy of interpreting cues.

“Distraction isn’t just about looking away,” one of the study’s authors, Petersen, said. “Talking on a cell phone can slow reaction time and make it harder to process what a cyclist is trying to communicate. Cyclists are already at a disadvantage. When a driver isn’t fully attentive, misunderstanding becomes more likely.”