Two motorists have been convicted of dangerous driving after their "classic case of road rage" resulted in a crash.
Dash cam footage shows the drivers repeatedly undertaking and tailgating each other on the M4 near Port Talbot.
Expert witness evidence showed the men reached speeds of up to of up to 101mph shortly before the collision on the eastbound carriageway.
The incident eventually led to one of the vehicles flipping onto its roof, the driver escaping unharmed.
The two men involved initially denied any wrongdoing but later pleaded guilty to dangerous driving at Cardiff Crown Court.
Police described the incident as "as classic case of road rage".
This incident was a classic case of road rage where two motorists have driven dangerously, at high speeds, undertaking, tailgating and flashing their lights. It is sheer luck that nobody was killed or seriously injured and the dash cam footage of the incident sends out a clear message about the consequences of driving in such an irresponsible manner.
Paul Carpenter, 44, from Boxhill in Surrey was sentenced to six months in prison and disqualified from driving for 18 months.
59-year-old Wayne Sebury from Pontypridd was given an 18 month community order and disqualified for 12 months.
He must also carry out 150 hours unpaid work.