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Clockwise – Hollow Square

Road users travelling clockwise are advised to follow the Hollow Square diversion symbol on road signs:

Exit the M25 at J21A and take the first exit onto the A405 towards St Albans.

At the A405/M10 Park Street Roundabout, take the third exit onto the A414 towards Hatfield.

At the A414/A1081 London Colney Roundabout, take the second exit onto the A1081 towards the M25.

At the next roundabout, take the second exit onto the slip road and rejoin the M25 at J22 towards Harlow.

Anti-clockwise – Hollow Square

Road users travelling anti-clockwise are advised to follow the Hollow Square diversion symbol on road signs:

Exit the M25 at J22 and take the third exit onto the A1081 towards St Albans.

Cross over the M25 and, at the next roundabout, take the second exit to continue on the A1081 towards St Albans.

At the A1081/A414 London Colney Roundabout, take the second exit onto the A414 towards Hemel Hempstead.

At the A414/A405/A5183/M10 J1 Park Street Roundabout, take the second exit onto the A405 towards Watford.

Follow the A405 to M25 J21A, then take the third exit to rejoin the M25 towards Heathrow.