Hope backed by hard evidence {supporting costs}

Below are the source figures behind ‘Hope backed by hard evidence’, grouped for easy reference.

Capital and long‑term costs

Estimated bridge capital cost: £300–350 million.
Design life: 120 years.
Annual equivalent capital cost: £2.5–2.9 million per year over 120 years.
Current annual ferry subsidy (2023/24): £2.09 million.
Net additional annual capital cost (bridge vs ferry subsidy): £0.41–0.81 million per year.

120‑year cost comparison

Bridge total 120‑year cost: £450–500 million (capital + operating + maintenance, NPV).
Ferry total 120‑year cost: £320.8 million, made up of:
- Ferry subsidy: £2.09 million/year → £250.8 million over 120 years.
- Vessel replacement (4 vessels): £40 million.
- Infrastructure renewal: £30 million.
Net additional investment (bridge vs ferry): £129.2–179.2 million over 120 years.
Annual equivalent of that net additional investment: £1.08–1.49 million per year.

Direct annual economic benefits

Components that add up to the £10.63 million direct annual benefit:

Current ferry fares burden: £1.43 million per year.
Vehicle operating cost savings: £3.2 million per year.
Journey time savings: £4.8 million per year.
Reliability benefit: £1.2 million per year.
Total direct annual benefit: £10.63 million per year.

Wider annual economic benefits

Components that add up to the £15 million wider annual benefit, subject to well oriented economic policies over time:

Tourism growth: £6 million per year.
Business efficiency: £4 million per year.
Employment access (labour market effects): £3 million per year.
Healthcare access improvements: £2 million per year.
Total wider annual benefit: £15 million per year.

Total annual benefit and 120‑year NPV

Total annual economic benefit (direct + wider): £25.63 million per year.

120‑year discounted (NPV) benefits:

Direct benefits NPV: £1.27 billion.
Wider economic benefits NPV: £1.8 billion.
Total benefits NPV: £3.07 billion.

Discounted costs for comparison:

Capital plus operating NPV: £450–500 million.

Benefit–cost ratio

Benefit–cost ratio range: 6.14:1 to 6.82:1, depending on whether the lower or upper bound of bridge cost (£450m vs £500m NPV) is used.

Question. If all factors turned sour, is SLC still viable ?

Yes. Even when you stack all the most pessimistic assumptions used in the independent work, SLC still clears the normal “viable” thresholds and remains in at least the High value‑for‑money band.

What “most pessimistic” looks like

Across the Quintin QS feasibility/economic material, the downside tests typically assume:

Higher bridge cost (towards £350m rather than £280–300m).
Lower traffic (about 30% below central forecasts).
Conservative time‑saving values and limited wider‑economic benefits.
Full allowance for ongoing maintenance, toll discounts and risk.

One explicit “low traffic” sensitivity test cuts crossings by 30% (Year‑30 use down to 900,000 trips), reduces toll revenue and increases net public cost, then re‑runs the appraisal.

Resulting BCR in that downside

In that low‑traffic, high‑cost scenario, the published result is BCR ≈ 2.6:1, which sits clearly in the UK TAG “High Value for Money” category (2.0–4.0).
Other conservative Green Book–style runs cited in the same work show SLC still above 2:1 when you combine pessimistic traffic with generous ferry assumptions, i.e. it remains better than the “do nothing / keep ferry” option on standard Treasury metrics.

Overall viability judgment

UK appraisal practice generally treats BCR > 1.0 as economically justified and >2.0 as a strong case; the pessimistic SLC scenarios stay safely above that line.
That means that, even if costs came in at the top of the campaign’s range and traffic under‑performed their central forecasts, the crossing would still be classed as a viable, fundable project in economic‑value terms rather than only “just about washing its face.”
When conpared to other Northern Ireland schemes, e.g. Knockmore Line or even Narrow Water Bridge, SLC would have a higher BCR.