Two break-even thresholds — and why both are honest
The appraisal can be done two ways, depending on what benefits are counted. Every figure on this tab comes from the Quintin QS feasibility dashboard engine at central inputs (£625m adjusted capex), unless stated.
Transport-only (TEE) break-even
~7,510 vpd
Counts transport user benefits only: journey time saving, vehicle operating costs, reliability. The narrow, most conservative test — it needs the most traffic. Against £625m adjusted capex (£500m ministerial ×1.25 HM Treasury optimism bias).
Full Green Book break-even
~4,740 vpd
Adds societal benefits: health gains, tourism, labour-market access, carbon. Lower threshold because more benefit is counted per vehicle. The standard HM Treasury Green Book / Better Business Case test adopted across NI public investment appraisal since 2021.
| Scenario |
AADT |
TEE result |
Green Book result |
| Today’s ferry |
650 |
BCR 0.10 ✗ |
BCR 0.35 ✗ |
| Full Green Book break-even |
~4,740 |
BCR 0.63 ✗ |
BCR = 1.0 |
| Low-demand stress (dashboard preset) |
5,650 |
BCR 0.49 ✗ |
BCR 0.81 ✗ (preset also cuts time saving to 24 min and halves traffic growth; 1.14 at central inputs) |
| Transport-only break-even |
~7,510 |
BCR = 1.0 |
BCR 1.44 ✓ |
| Pessimistic (dashboard preset, £1,209m adj capex) |
9,650 |
BCR 0.47 ✗ |
BCR 0.69 ✗ |
| Central (Yr 5) |
13,650 |
BCR 1.81 ✓ |
BCR 2.41 ✓✓ |
| High (Corran-class) |
16,000 |
BCR 2.12 ✓ |
BCR 2.78 ✓✓ |
How the ~7,510 vpd figure is derived: The dashboard engine’s transport-user-only BCR (journey time, vehicle operating costs, reliability; TAG values; Green Book 2025 declining discount rate) at central inputs, with break-even found by bisection on total Yr 5 AADT. Hand check: £625m ÷ 60-yr annuity factor ~24.9 ≈ £25m/yr; at ~£8 benefit per return trip that needs ~8,560 vpd — the same order. Correction (23 Sep 2026): earlier versions of this page showed 285 vpd. That was an arithmetic error — 285 vpd × £8 × 365 is only ~£0.8m/yr — and the statement that today’s ferry traffic already clears this test was wrong. At 650 vpd the transport-only BCR is 0.10.
How the ~4,740 vpd figure is derived: From the Quintin QS feasibility dashboard’s full appraisal engine, which adds societal benefit streams (tourism £95–110M, labour-market access, health gains) and carbon to the transport user benefits. Break-even located by bisection on total Yr 5 AADT at fixed central inputs. Under the dashboard’s Treasury 7% discount-rate preset it rises to ~10,890 vpd; under the Pessimistic preset to ~14,970 vpd. Both calculations use the same £625m adjusted capex anchor.
Capex anchor: £500m stated by Minister Kimmins, Assembly 11 May 2026. Adjusted by HM Treasury standard optimism bias of 1.25× =
£625m. DfI source document (FOI DFI-2024-0412, 7 Aug 2024) described its own estimate as a “very rough cost estimate.” The Quintin QS evidence-based component build-up gives £321m (pre-OB), £350m (reduced OB). Full methods:
feasibility dashboard →