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The A21 was closed in both directions after the air ambulance was called to a serious crash on bank holiday Monday.
The collision, involving a motorcycle, shut the Tonbridge Bypass between the A26 Quarry Hill Road and A26 Woodgate Way near Tonbridge.
Initially, both London-bound and coastbound carriageways were closed to allow the air ambulance helicopter to land.
The London-bound carriageway reopened shortly before 1pm and the coastbound section was reopened at about 2.15pm.
Hundreds of bikers were on their way to Hastings for the annual May Day Run today, billed as the "biggest free-to-enter motorcycle event in the world."
A police spokesman had warned shortly after the collision: "The A21 is currently shut near the junction for Tonbridge following an earlier collision involving a motorcyclist. Lengthy delays are expected."
Highways England introduced a number of diversions for motorists.
A Highways England spokesman added at the time: "Road-users in the area should allow additional time for their journeys.
"Local roads are expected to be heavily congested while the A21 Tonbridge Bypass remains closed."
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