Highways officials have reopened the A414 and the A4147 roads in Hemel Hempstead and St Albans after closing them for more than 24 hours.
The roads were closed at 3am on Monday because smoke from a fire at a recycling centre in Appspond Lane was blowing onto the road.
A Hertfordshire County Council spokesman said that the roads will be open for the time being and fire crews are on standby to close them if smoke from the fire starts blowing in the road again.
Firefighters have been trying to get the blaze under control at the centre since Saturday night.
Crews from Hemel Hempstead, Watford and Wheathampstead have been using water jets and hose reels to douse the massive pile of recycled wood at the centre, which is on the border of Hemel Hempstead and St Albans.
Herts Fire Service spokesman David Henning said: “There was quite a considerable amount of recycled wood so there’s plenty of scope for it to burn at a considerable pace.”
The alert was raised at 11.45pm on Saturday and a number of fire crews have been working to keep the blaze contained.
The A414 and the A405 were closed in both directions between King Harry Lane in St Albans and Breakspear Lane in Hemel Hempstead.
A diversion from the A414 St Albans Road directed traffic to the A41 Watford Road, A41 Gadeside and A405 North Orbital Road.
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