The man, identified only by his surname Cai, was seen in surveillance footage painting his own arrows at a junction in the eastern city of Lianyungang to redirect the traffic as cars manoeuvre past him, the regional Modern Express newspaper said.
Police in Jiangsu province fined the 28-year-old 1,000 yuan ($150) after he was spotted crouching in the middle of the busy road with a can of white paint, according to the paper.
"I take the bus to go home after work every day, passing by that place," Cai said in what appears to be a police video obtained and published by the newspaper.
"The traffic jam there is always pretty bad but I saw there are only a few cars in the lane that turns left so I just want to expand one driving lane by adding one straight arrow."
Authorities later ordered maintenance workers to remove Cai's handiwork from the road, but police released him after fining him.
"Considering that you are still young and quite honest, we won't detain you this time, understand?" a policeman is heard telling him in the video.