Avon & Somerset Police are appealing for spectators with video or photos of the fatal accident to contact them.
The crash happened as 23-year-old cyclist Junior Heffernan came round a bend during the Severn Bridge Road Race.
Here is Acting Inspector Darren Jarvis...
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A 52-year-old man has been arrested on suspicion of murder and he remains in custody.
An overcast start with cloud spreading from the east to Devon and Cornwall. Cool winds and isolated showers in parts of South Devon
An overcast start with plenty of cloud filling in from the east. Some isolated showers in Somerset and Dorset. Highs of 8 or 9 degrees.