Roads affected
The restrictions also cover the westbound A414 from London Colney Roundabout to Park Street Roundabout, along with both directions of the A405 North Orbital Road between Tippendell Lane and Park Street Roundabout.
Access to and from the roundabout via the A5183 Watling Street South will also be closed, including from 8 p.m. to 6 a.m. on Thursday. No closures are scheduled for November 6, 7 or 8. Signed detours will guide drivers during the work.
A SEGRO spokesperson said: "We would like to thank you for your cooperation during these works and we will continue to provide updates as the works progress."
New lanes, signals and drainage
SEGRO's construction schedule describes a mix of daytime and overnight work at Park Street Roundabout, with localized closures. The changes include another entry lane from the A405, an exit lane on the eastern A414 arm and a third lane around the roundabout.
Traffic signals are planned for the A414 and A405 approaches to make it easier to enter from Park Street and Watling Street. The work also includes improvements to the A405 pedestrian crossing, greater drainage capacity to address existing and future flooding, and upgrades to existing services.
According to SEGRO, the roundabout is part of a £40 million investment in Hertfordshire County Council's highways that requires no county council funding. The package also covers the Park Street/Frogmore relief road, the development's main access roundabout, London Colney Roundabout and M25 junctions 21a and 22.
Development plans and traffic concerns
The road work forms part of SEGRO's disputed development at the former Radlett Aerodrome. Campaigners have challenged the project, including through an unsuccessful High Court appeal. Opponents argue that the freight terminal will bring thousands of additional trucks and vans onto roads that are already congested.
SEGRO acquired the 419-hectare site on June 30, 2023, for £120 million, with half the payment deferred for 12 months. The purchase brought together three parcels owned by Hertfordshire County Council, Tarmac Plc and Gorhambury Estates Company Ltd.
The approved development allows up to 3.6 million square feet of logistics space in seven warehouses, alongside a rail freight terminal. The largest warehouse would cover approximately 1.2 million square feet. A 247-hectare country park is planned around the terminal.
SEGRO chief executive David Sleath said the project will "benefit the national and local economies." The company anticipates around 4,000 jobs once the scheme is complete, approximately 500 on-site construction jobs and about £12 million in annual business rates.
The scheme also includes £22 million for a new 1.4-mile Park Street/Frogmore relief road, which SEGRO says is intended to ease traffic on the A5183. In support of rail freight, the company cites industry figures putting its contribution to the UK economy at £1.7 billion and estimating that each freight train removes up to 76 heavy goods vehicle journeys from Britain's roads.
Construction contracts and timetable
STRABAG UK has secured SEGRO's contract for the next and final infrastructure phase at SEGRO Logistics Park Radlett. Its scope includes preparing the terminal and warehouse plots, building the surrounding bund and private estate roads, and delivering the rail terminal itself. Off-site work includes A414 and M25 junction improvements and a new road bypassing Park Street and Frogmore.
SEGRO says the main earthworks, infrastructure, highway and utility work started in the second half of 2025, with completion expected during 2028. Construction of the buildings is anticipated between 2027 and 2030.
Warehouse occupancy depends on the Strategic Rail Freight Interchange being capable of operating. SEGRO says that point will not be reached until mid-2027.
