Traffic Idioms (American idioms)
美 式交通的慣用語


explanation : This common idiom refers to the part of the car called the 'bumper' in the front and rear of the car.  It means that traffic is so slow, the bumpers of the cars are almost touching.  In other words, traffic is almost stopped.

e.g.  In Los Angeles, the traffic on the freeways is always bumper-to-bumper at 5:00 pm.