Transport for London Marylebone Flyover Rain Gardens
3,500m² SuDS · largest sustainable drainage system in central London · £1.7m construction
TfL met 70% of its 2024 annual SuDS installation target from this single project. Repurposing existing disused space (subway ramps/stairs) eliminated the need for costly deep excavation in a busy central London carriageway.
Nine rain gardens (bioretention areas) were installed on the A5/A40 Marylebone flyover intersection in central London, repurposing a disused subway station to create 3,500m² of SuDS — the largest sustainable drainage system in central London. Completed 2024, the scheme handles storms from 1-in-5 to 1-in-20 years, with no flooding in surrounding streets recorded since installation.
Climate drivers
Impacts
Adaptation measures
- Rain gardens (bioretention)
- Sustainable Drainage Systems (SuDS)
- Silt traps
- Street tree planting
Assets affected
Investment
£729k design fees; £1.7m construction; £1m GLA Green Infrastructure Fund grant
Band: £1m–£10m
Delivery period
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- The Marylebone flyover faced climate hazards from heavy rainfall, particularly surface water flooding and overflowing of combined surface-foul drainage. These hazards had become more prevalent over time due to more frequent heavy rainfall events.
- The Marylebone flyover is a 3.5-mile elevated dual carriageway section of the A40 in west London that was constructed between 1964 and 1970.
- The stairs and ramps that were historically used to access a disused underpass were transformed into Sustainable Drainage Systems (SuDS).
Ref: ID_13 · Transport for London · Curated & verified by HIVE
Directly applicable to UK urban road junctions experiencing surface water flooding where disused underground or sub-surface infrastructure can be repurposed. The retrofit SuDS model minimised road disruption — a key benefit for busy urban highways.
UK contexts
London & South East
Transfer to other sectors (AI)