A man was taken to hospital with a suspected fractured pelvis following a collision between a cyclist and a car on the outskirts of King's Lynn.
The A149 at Queen Elizabeth Way was closed for much of the afternoon between Knights Hill and the Castle Rising junction while accident investigators worked at the scene.
Motorists faced delays, particularly during the evening rush hour, as diversions were put in place to avoid the stretch of road, which is a busy route to the North West Norfolk coast.
The road reopened at around 8pm.
An officer at the scene said: 'The road is currently closed because we are investigating a serious road traffic collision - and we expect it to remain closed for some time.'
The emergency services were called the collision at around 3.15pm yesterday.
The Norwich East Anglian Air Ambulance was also dispatched to provide further medical support and the patient taken to the Queen Elizabeth Hospital in King's Lynn by land ambulance.
Richard Bass, 50, who works at the Knights Hill Farm Shop, said: 'I've worked here for about 10 years and traffic accidents happen quite often along all the roads around here.'
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