The What Makes You Beautiful hitmakers were travelling from London's Heathrow Airport on Sunday after performing in Japan when the accident occurred.
Bandmates Harry Styles, Zayn Malik, Liam Payne and Louis Tomlinson were in two separate people carriers when Horan's 4x4 Range Rover slid into a barrier near traffic lights on a road leading from the airport.
Horan reportedly emerged shaken, but unhurt, from the passenger seat of the vehicle.
An onlooker told Britain's The Sun newspaper: "They all waved as they went past, then the crash happened so suddenly. It must have been terrifying - the car's wheels lifted off the road.
"We saw Niall climbing out. He looked shaken up but didn't seem hurt. He got into a people carrier and they drove off again."
This is not the first car accident to affect the group - last January the band suffered whiplash when a vehicle struck their tour bus in Birmingham, England.