About the project
We’re delivering a major upgrade to the drainage network on La Grande Route de St Jean from St Helier Municipal Services Depot (north of Mont à l’Abbé School) to Sion.
The project will take place from November 2025 to February 2027.
To reduce disruption, construction will be split into sections called works areas, with full road closures limited to those sections.
Access for residents and businesses will be maintained during the works and diversion routes will be in place.
We’ll update the information on this page as the work progresses.
Why it’s needed
With the sewer network under La Grande Route de St Jean already operating at full capacity, our drainage systems must evolve to cope.
This upgrade is part of a broader commitment to ensuring our Island is protected, connected and prepared for the decades ahead.
We’re carrying out this major upgrade to:
- protect homes, businesses, and the environment
- reduce flood risk
- connect existing homes to the network
- support new housing development
- invest in and strengthen our Island’s infrastructure
The work will be delivered in phases over the next few years and will increase sewer capacity from the Haute Croix area to the Bellozanne Sewage Treatment Works (STW).
Project details
The existing 400mm pipes on La Grande Route de St Jean will be replaced with a larger 600mm pipes to handle higher flows from Sion to the Bellozanne STW.
Full road closure of La Grande Route de St Jean is needed during construction because:
- the existing sewers to be replaced are mainly located beneath the centre of the road
- properties on either side of the road need to be reconnected to the new sewers
- the new sewers will be buried 2 to 4 metres below the road surface, and the contractors need to work safely and efficiently
The project has been split in small sections (works areas) to reduce disruption, with road closures limited to those sections. The working area will move along the road as works is completed.
There will be 2 contractors working at the same time to help complete the project as quickly as possible. This means that there may be more than one section of La Grande Route de St Jean closed at a time.
Schedule of work
Full road closures will be in place for each section. We’ll publish specific dates for each closure before they start.
More details will be added as the project develops. Dates may change as the work progresses.
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1 | La Grande Route du Mont a l'Abbe, across the junction with Le Vert Chemin
| January 2026
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2 | Le Vert Chemin | January to mid-March 2026
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3 | La Grande Route de St Jean, across the junction with Le Vert Chemin
| Late January to mid-March 2026
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4 | La Grande Route de St Jean, north of the junction with Le Vert Chemin, to south of the crossroads with La Rue de Maupertuis and La Rue du Haut de l'Orme
| Mid-March to January 2027 |
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5A | La Grande Route de St Jean, across the crossroads with La Rue de Maupertuis and La Rue du Haut de l'Orme
| February 2027
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5B
| La Grande Route de St Jean, a short section north of the crossroads with La Rue de Maupertuis and La Rue du Haut de l'Orme
| February 2027
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6 | La Grande Route de St Jean, north of the crossroads with La Rue de Maupertuis and La Rue du Haut de l'Orme, to south of the crossroads with La Ruette Pinel and La Rue du Becquet Vincent
| 3 November 2025 to February 2026 |
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7 | La Grande Route de St Jean, across the crossroads with La Ruette Pinel and La Rue du Becquet Vincent. | Mid-February 2026 |
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8 | La Grande Route de St Jean, north of the crossroads with La Ruette Pinel and La Rue du Becquet Vincent, to south of the junction with La Rue des Hougettes
| Late February to mid-October 2026 |
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9 | La Grande Route de St Jean, across the junction with La Rue des Houguettes
| Mid-October 2026 |
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10 | La Grande Route de St Jean, north of the junction with La Rue des Houguettes to north of the United Reformed Church, Sion
| Late October to December 2026.
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Diversion routes
Traffic diversion routes will be added to this page ahead of each road closure.
Diversion map Phase 3 to 10 (southbound)
Diversion map Phase 6 (northbound) -
La Grande Route de St Jean
Diversion map phase 6, 7 and 8 - Rue des Servais and Les Hamonnets
HGV
HGV diversion map Phase 3 to 10
Access
Access to all businesses, car parks and residential properties in the surrounding area will be maintained during the works.
Bus
The bus service will remain in service on diversion for the duration of the works.
Details of bus diversions and bus stop suspensions will be published nearer the time on
LibertyBus.
Contact information
If you have any questions about the project:
- email
LWCapitalDelivery@gov.je
- call +44 (0) 1534 445509. Select option 3
for Drainage and Sewerage, then option 4 for the Liquid Waste Capital Delivery team
If you have any feedback about the project, you can send them to the Liquid Waste Capital Delivery team by submitting the online feedback form below.
Send your feedback
All feedback will be handled in line with our
Customer Feedback Policy.
gov.je