Police were called to the fourth accident thought to be caused by icy conditions this morning.
Just after 9am, a male motorbike rider was treated for 'serious' leg injuries and taken to Royal Cornwall Hospital in Truro after the accident in Bassett Road, near Redruth.
A police spokesman said: “Road conditions were obviously difficult this morning and I would urge motorists to slow down and take extra care.
"We have received numerous reports of ice on the roads and whilst the conditions may appear to have improved there still could be patches of untreated roads which remain dangerous”.
The accident followed three others between 8am and 9am on the A394 near Penryn, the B3297 near Helston and the A390 near Lostwithiel.