A burst water main is likely to cause delays today and over the weekend.
Affinity Water has been called to the A404 Chorleywood Road this morning to carry out emergency repairs.
Hertfordshire County Council has confirmed the water supplier is attending a burst water main.
Two-way traffic lights have been put up near the junction with The Clump.
The council is warning drivers to expect delays on this route which connects Chorleywood and Rickmansworth, and is close to junction 18 for the M25.
The council has given Affinity Water a permit of until next Wednesday to complete the work - but the work may be completed sooner or later of that date.
Two-way traffic signals are also in place in Uxbridge Road in the Moneyhill area of Rickmansworth.
Carriageway repairs are taking place until Wednesday.
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