A motorcyclist died and two others were injured in three separate accidents.
They happened on the same day that the Ace Café Reunion filled Brighton seafront with thousands of bikers and their machines.
The death of Gary Robinson, 47, from Westfield in Harlow, Essex, happened at about 4pm yesterday.
Mr Robinson appears to have lost control of his silver Yamaha XJR 1300 while travelling north on the M23 near Crawley.
He crashed and was thrown into the southbound carriageway where he was struck by a trailer.
The trailer was being towed by a Mercedes Sprinter van, driven by a 29-year-old man from Coulsdon in Surrey.
Sussex Police said that Mr Robinson was thought to be travelling home from the Ace Café event in Brighton.
Inspector Andy Judson, from the Sussex Police Road Policing Unit, said: “It is not clear at this time what caused the motorbike to lose control.
“But the result was devastating and extremely distressing for the many people who witnessed the collision or its aftermath.
“The northbound carriageway was closed for about five hours and the southbound reopened around 11.15pm.
“I appreciate that this caused considerable disruption in the area, but it was a complex recovery, investigation and clean up operation.
“I should like to thank people for their patience and understanding.
“A number of witnesses have come forward but if you have not yet spoken to us please call 0845 6070999.”
Two other motorcyclists suffered broken legs – one in an accident in Hove and the other in Brighton.
A 33-year-old biker from London broke his leg after colliding with two cars and a bus shelter on the A23 London Road in Brighton yesterday just after 2.35pm.
The man was travelling southbound near the junction of Varndean Road when he was in collision with a red Citroen C4 and a blue BMW 330 convertible before hitting the bus shelter.
He was taken to the Royal Sussex County Hospital in Brighton.
Traffic was diverted away from the scene and the road re-opened at around 5.30pm.
In Hove a 20-year-old motorcyclist suffered a broken leg after being in a collision with a burgundy Ford Focus at about 6.25pm.
He was also taken to the Royal Sussex County Hospital.
