- BY Kevin Barry BSc(Hons) MRICS
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Strangford Lough Crossing: Comparing All Five Options
An independent assessment of the crossing options — and what the evidence says
The debate around a permanent crossing of Strangford Lough is often reduced to a single question: bridge or no bridge? In reality, five distinct options exist. Each has been assessed on capital cost, journey time, daily capacity, benefit-cost ratio (BCR), 24/7 availability and 120-year lifecycle cost. What follows is a plain-language summary of that assessment.
Option 1 — Fixed Bridge (Cable-Stayed)
Rank: 1st
A high-level road bridge at the Narrows, with a walking and cycling path, is the top-ranked option on every meaningful metric.
An independent cost analysis, benchmarked against the Queensferry Crossing, the Rose Fitzgerald Kennedy Bridge in New Ross and the Narrow Water Bridge, places the capital cost at £300–350 million in 2025 prices. This is the figure Minister Kimmins referenced in the Assembly on 3 February 2026 — and it is consistent with professional quantity surveying analysis, not with the Department’s previously quoted £650 million figure, which FOI disclosures revealed was based on crude scaling rather than engineering detail.
The bridge would cut the current crossing time to 8 minutes, 24 hours a day, 365 days a year, in all weather conditions. For comparison, the road detour when the ferry is unavailable is 75 km and takes approximately 90 minutes.
Using DfT Transport Appraisal Guidance (TAG) methodology, the benefit-cost ratio is assessed at 2.5 to 3.5, placing the scheme in the UK Government’s “High Value for Money” band. When wider economic benefits are included over a 120-year design life, the BCR rises further.
The 120-year total cost (capital, operation and maintenance, net present value) is estimated at £450–500 million. The cumulative cost of maintaining the ferry over the same period, including subsidy and vessel replacement, reaches £320 million — without resolving the fundamental access deficit.
Key characteristics: 24/7 all-weather access · Walk/cycle provision · 4,000+ vehicles/day capacity · 120-year design life · Moderate planning consent complexity
Option 2 — Enhanced Diesel Ferry
Rank: 2nd
An upgraded diesel ferry service with new or refurbished vessels and improved pier facilities represents the lowest upfront capital commitment at £15–25 million. It is, in effect, the do-minimum option.
However, the annual operating subsidy stands at £2.09 million for 2023/24 — and has risen by approximately 40% in 12 months. Over 120 years, cumulative ferry costs reach £320 million, and that figure does not capture the economic penalty imposed on peninsula communities by the service’s fundamental constraints: limited operating hours, weather dependency, and a vehicle capacity of approximately 650 per day, on average.
The BCR for this option is assessed at 0.8 to 1.4 — marginal at best, and significantly below the bridge. It does not resolve the 75 km night and weekend detour that affects residents, emergency services, businesses and visitors.
Key characteristics: Limited hours · Weather dependent · No detour solution · Subsidy rising · ~650 vehicles/day
Option 3 — Bored Tunnel
Rank: 3rd
An immersed or bored road tunnel beneath the Narrows is technically feasible and would provide 24/7 all-weather access with no visual impact on the Lough. Those are genuine advantages.
The difficulty is cost. Capital is assessed at £450–600 million — between 40% and 70% more than the bridge for equivalent traffic capacity. DfI’s own internal papers acknowledge that any tunnel option would be “in excess of a bridge solution” in capital terms, even before accounting for the higher complexity and risk allowances that tunnels require. Portal access shall be well away from the coastline and given the depth of Strangford Lough, lesser solutions like cut and cover immersed tube solutions shall not be feasible.
The BCR is assessed at 1.2 to 2.0 — viable, but substantially weaker than the bridge. Lifecycle costs over 120 years are estimated at £700–850 million.
A tunnel also cannot accommodate walking or cycling, and construction would involve more intrusive marine works — portals, cofferdams, dredging and spoil disposal — creating a different but potentially more contentious environmental impact than a well-designed bridge despite the lower visual profile.
A tunnel would only become the preferred option if strict visual-impact requirements ruled out a bridge entirely.
Key characteristics: 24/7 access · No walk/cycle · 40–70% costlier than bridge · Complex marine geology · No visual impact on Lough
Option 4 — Electric Ferry
Rank: 4th
Electric ferry technology is advancing rapidly. Vessels similar to the Norwegian Ampere class or those under trial by Caledonian MacBrayne would reduce operational carbon to near zero and modestly improve crossing time to around 20 minutes with capacity of approximately 1,100 vehicles per day.
The capital cost for new vessels and pier charging infrastructure is assessed at £18–30 million, making this the lowest upfront option alongside the diesel ferry. Lifecycle costs over 120 years are estimated at £280–320 million — marginally below the diesel ferry, primarily through lower fuel costs.
However, the BCR of 0.7 to 1.3 reflects the same fundamental problem as the diesel option: the service still operates limited hours, remains weather dependent, and does nothing to solve the 75 km detour when the crossing is unavailable. The subsidy obligation continues.
An electric ferry upgrade has merit as a transitional measure if a fixed crossing is delayed. It should not be presented as a long-term solution to a permanent access problem.
Key characteristics: Near-zero operational emissions · Faster than diesel ferry · Still limited hours · Subsidy remains · Charging infrastructure required
Option 5 — Tidal Barrage / Causeway
Rank: 5th
A full tidal barrage or causeway across Strangford Lough would provide 24/7 access at the highest theoretical vehicle capacity of any option. It is included here for completeness.
The capital cost is assessed at £800 million to £1.2 billion — three to four times the bridge cost. More fundamentally, Strangford Lough is a Special Area of Conservation (SAC) and Special Protection Area (SPA), one of the most ecologically sensitive inlets in Europe. A barrage would cause irreversible damage to tidal hydrology, intertidal habitats and migratory species. Consent under current Habitats Regulations is effectively impossible.
The BCR is assessed at 0.3 to 0.9. This option is not viable.
Key characteristics: Effectively unbuildable · Cost 3–4× bridge · Strangford SAC/SPA incompatible · Highest capacity if built
The Verdict
The independent evidence consistently points to the same conclusion. A fixed bridge at the Narrows is the only option that resolves the access problem permanently, delivers value for money under standard UK appraisal methodology, and is deliverable within realistic budget parameters — particularly with Irish Government co-funding through the Shared Island Fund, as demonstrated by the Narrow Water Bridge.
The five-option comparison is summarised in the table below.
| Option | Capital Cost | Journey Time | BCR | 24/7 Access | Rank |
|---|---|---|---|---|---|
| Fixed Bridge | £300–350m | 8 min | 2.5–3.5 | ✓ Yes | 1st |
| Enhanced Ferry | £15–25m + subsidy | 25 min | 0.8–1.4 | ✗ No | 2nd |
| Bored Tunnel | £450–600m | 10 min | 1.2–2.0 | ✓ Yes | 3rd |
| Electric Ferry | £18–30m + subsidy | 20 min | 0.7–1.3 | ✗ No | 4th |
| Tidal Barrage | £800m–£1.2bn | 10 min | 0.3–0.9 | ✓ Yes | 5th |
All costs in 2025 prices. BCR calculated using DfT TAG methodology. Journey times reflect direct crossing. Ferry subsidy: DfI 2023/24 figure of £2.09m/yr.
Analysis prepared by Kevin Barry BSc(Hons) MRICS, Quintin QS — Campaign Lead, Strangford Lough Crossing.