Carriageway reconstruction: how we resolved noises and vibrations on Hampden Way

Metis was appointed by the London Borough of Barnet to support the full carriage reconstruction and drainage redesign of Hampden Way, a 1.2km strategic residential route in Southgate.

As both a main distributor road and a key bus corridor, Hampden Way had experienced progressive deterioration over the past decade, driven primarily by surface water movement through the carriageway layers. This had prompted complaints from residents, who were experiencing noises and vibrations in their houses as a result. Barnet commissioned us to undertake both highway drainage design and full carriageway reconstruction design to improve long‑term performance and resilience.

Building on the Phase 1 carriageway reconstruction and drainage redesign, we then delivered additional Phase 2 active travel improvements and provided on‑site programme management support to ensure effective coordination between Barnet and TKJV.

The Challenge

Investigations undertaken by Barnet and Capita revealed that the primary cause of pavement failure was water ingress. Over time, surface water flows from the east had washed out material at the asphalt–concrete interface, leading to delamination and accelerating surface defects. While parts of the route had been resurfaced in 2019, this did not address the underlying issue. Barnet required a robust engineering solution capable of withstanding a 1 in 30‑year storm (plus climate change allowance) and extending the design life of the carriageway.

Key issues included:

• Chronic surface water infiltration through pavement layers
• Localised washout beneath the asphalt surfacing
• Need for a high‑resilience drainage strategy
• Requirement to determine whether full reconstruction was necessary along all sections
• Integration of multiple investigations including GPR, coring, trial holes, and additional surveys necessary for design development

There were additional residential concerns to take into account: while residents were keen for the issue to be resolved, they also had to consider that their road would be closed for six to nine months.

Our Approach

Metis adopted a two‑stream design approach – drainage and pavement reconstruction – ensuring the solutions complemented each other and delivered long‑term performance.

Comprehensive Pre‑Design Review

We undertook a full review of existing investigations, including the Capita options report, GPR surveys, pavement coring, and trial hole records. Additional surveys were specified where gaps existed, such as:

• CCTV surveys of drainage assets
• Infiltration testing
• DCP testing to support pavement design

This ensured the design was grounded in a full understanding of site constraints and failure mechanisms. Most prominent among these were utilities considerations: the road had to be reconstructed around existing water and gas lines.

Highway Drainage Strategy

• We prepared a concept and detailed drainage design aligned with Barnet’s requirement for a 1 in 30‑year storm event, far exceeding the typical 1 in 5‑year standard. The design package included:
• Review of existing flow paths and subsurface water behaviour
• Identification and confirmation of suitable outfall locations
• Optimised pipe sizing, inlet spacing and drainage layout to mitigate long‑standing groundwater and surface water issues
• Inclusion of fin drains to collect surface water that does infiltrate

Carriageway Reconstruction Design

Based on pavement deterioration and sub‑surface conditions, we developed a full reconstruction solution using flexible construction with a 25‑year design life. The previous road had been built with a concrete base around the 1920-30s: our new design removed the concrete slabs causing vibrations to nearby houses, and replaced them with more flexible asphalt. Deliverables included:

• Preliminary pavement design with materials assessment
• Detailed design drawings compliant with MCHW standards, including General Arrangement, Site Clearance, Pavements, Kerbs/Footways, Ironworks and Markings
• Design decisions captured in registers to ensure transparency and traceability
• Considerations for sustainability, noise reduction, buildability and minimising property vibration

Active Travel and Streetscape Improvements (Phase 2)

To complement the engineering works, we developed improvements aligned with Barnet’s active travel aspirations. Measures assessed included:

• Review of pedestrian crossing points, including new opportunities near schools
• Improvements to bus stop configuration and accessibility
• Speed‑management interventions
• Parking rationalisation and verge‑parking issues
• Junction protection measures
• Opportunities for SuDS features at verges, school‑frontage areas and locations with wider splays
• Consideration of cycle permeability, including potential parallel crossings at the southern end

Project Governance and Collaboration

Metis acted as Principal Designer (up to construction stage) on the reconstruction design and ensured a governance framework that supported quality assurance, specialist input, and seamless communication with Barnet. Regular progress reviews and design workshops helped confirm assumptions and maintain programme certainty.

To support coordination between TKJV and Barnet, we provided a dedicated Programme Management Officer. Responsibilities included: programme monitoring and updates; early identification of risks and blockers; facilitating communication between stakeholders; supporting progression of drainage‑related projects; and providing monthly reporting and governance oversight

This support ensured alignment between design development, procurement and delivery activities.

Outcome and Value Delivered

The combined drainage and reconstruction design provides Barnet with a robust and long‑term solution for one of its key distributor roads. The approach directly addresses the root causes of historic pavement failure (surface and groundwater infiltration) while delivering a resilient, maintainable and cost‑effective design ready for carriageway reconstruction.

Key benefits delivered:

• Improved quality of life for residents, pedestrians, cyclists and bus passengers
• A fully engineered drainage solution designed for future climate resilience
• A 25‑year pavement design tailored to local conditions and loading
• Reduced long‑term maintenance risk, driven by addressing groundwater challenges at source
• Improved road performance and safety for residents, bus operations and local traffic
• Clear, audited design rationale through technical notes and decision logs
• A suite of active travel, safety and accessibility improvements designed in close alignment with Barnet’s priorities
• Reduced long‑term maintenance risk
• Improved quality of life for residents, pedestrians, cyclists and bus passengers

The Phase 1 and Phase 2 works together create a future‑proofed corridor that enhances safety, sustainability and long‑term performance for the community.

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