Phantom traffic jam

 A phantom traffic jam(or traffic wave/ghost jam)is  a sudden, unexplained backup on a highway,caused by a ripple effect from one driver,braking slightly,forcing the car  behind to  brake harder,and so on, amplifying the showdown until cars stop,even without an accident or construction.These jams form in dense traffic due to human reaction times and lack of sufficient spacing,with the "wave" of congestion moving backward through traffic.