What a BCR actually counts

A benefit-cost ratio (BCR) is a single number, but it is assembled from layers of benefit. This analysis takes the two Irish rail lines with full published appraisals — the Western Rail Corridor (WRC) and the Navan line — and rebuilds each BCR layer by layer from the official figures. It shows what the number actually counts, and overturns a common intuition: widening the accounting boundary barely moves the ratio. Demand does. This is the worked detail behind the "contested" verdict the WRC carries in Analysis 1.

Headline findings

• Both lines fall short of break-even. The WRC's official BCR is 0.21; the Navan line's preferred option is 0.71. Every published Irish BCR for these lines is below 1.0 — benefits do not cover costs. (official)
• Widening the boundary is second-order. Going from the standard direct-transport case to the full social cost-benefit analysis (CBA), the WRC moves from 0.24 to 0.21 and Navan from 0.68 to 0.71. The accounting boundary is not what separates them. (measured from the appraisals)
• Demand is the whole story. The gap between a hopeless line and a near-miss opens at one step — direct user benefits. Navan's commuters generate about €322m of journey-time savings; the WRC's rural traffic shows a time disbenefit. (official)
• Environmental benefits are a small net cost here, not a saviour. In both appraisals, emissions and noise net to a disbenefit — the rolling stock is diesel until electrification. Carbon does not rescue either case. (official)
• Cost-cutting alone cannot save the WRC. Even halving the cost leaves it near 0.42; break-even would need roughly an 80% cost cut and far higher demand. That is why it is a strategic, not an economic, case. (modelled from EY figures)
• Navan is a near-miss trending the wrong way. Favourable assumptions reach 0.86, but the headline cost estimate has risen from about €0.8–1.1bn (2021) toward €2–3bn (2024), which pushes the ratio down. (official)

1. What a benefit-cost ratio counts

Ireland appraises major transport schemes with social cost-benefit analysis, under the Department of Public Expenditure's Public Spending Code (PSC) and the Department of Transport's Common Appraisal Framework (CAF). A scheme's benefits are added up in widening layers — the same four layers used in Analysis 1:

1. Farebox — the fares passengers pay. Almost never covers the cost on its own.
2. + Direct transport — journey-time savings, vehicle-operating-cost savings, reliability and road safety. This is the standard CBA boundary, and where most of the value sits.
3. + Wider economic — agglomeration (firms more productive in a denser labour market) and land-use change.
4. + Environmental & social — carbon, air quality, noise, access and equity.

The BCR is the present value of all counted benefits divided by the present value of costs; a ratio of 1.0 is break-even. The two lines below are the only Irish reopening/newbuild proposals with a full published CBA, so they are the only ones where we can see every layer. Both use the same PSC/CAF framework, which makes the shape of the two appraisals comparable even though the detailed assumptions differ.

A like-for-like caveat. The two appraisals are not identical in their mechanics: EY valued the WRC in 2019 prices over a 30-year horizon; AECOM valued Navan in 2011 prices over a 60-year horizon (30 years plus a 30-year residual). So the absolute BCRs should not be compared to the last decimal place. What is comparable — and what this analysis relies on — is the layer-by-layer shape within each appraisal, and the demand story that separates them. Full parameters are in the key-figures box.

2. Worked example — the Western Rail Corridor

The WRC's Athenry–Claremorris section is state-owned and physically intact. In 2020, EY and Mott MacDonald appraised its reinstatement for Iarnród Éireann. The capital cost was put at €263.8m (about €325.3m in present-value terms), carrying roughly 575,000 passenger journeys a year by 2030. Rebuilding the published result layer by layer:

Two things stand out. First, the dominant benefit is travel-cost savings (+€73m), not journey time — because on these rural origin-destination pairs the train is not actually faster than the car, so journey time is a net disbenefit (−€18.3m). Second, widening the boundary does nothing to help: the wider-economic benefits were assessed and found negligible, and emissions and noise net to a disbenefit. The published all-in ratio is 0.21 — for every €1 invested, society gets back about 21 cents — and EY's own sensitivity analysis left even the best case deeply negative (net present value −€198m).

3. Worked example — the Navan line

The Navan line is a new 34 km electrified branch from the existing network at M3 Parkway to Navan, with four new stations, carrying up to 1.8 million journeys a year. In 2021, AECOM appraised it for the National Transport Authority (NTA). The preferred rail option (Option A) was costed at €777m–€1,122m (2021, excluding VAT). Rebuilding its published BCR:

Here the picture is completely different at one layer — direct transport. Navan's commuters into a congested Dublin generate about €322m of journey-time savings and large user benefits (+€402m), lifting the ratio from 0.04 to 0.68 in a single step. Agglomeration adds a little more (+€32m, to 0.73), and — as with the WRC — environmental effects net slightly negative, because the service runs diesel rolling stock until the fleet electrifies around 2045. The published ratio is 0.71, rising to 0.79 on higher growth.

A moving target. AECOM's €777m–€1,122m is the 2021 build-cost range. Since then the NTA has indicated the figure has risen with construction inflation toward €2–3bn (reported December 2024). Because benefits are broadly fixed, a cost of that scale would push the BCR materially below the 0.71 shown here — the opposite direction to the "further design could improve it" hope in the original report.

4. What actually drives the ratio

Plotting both appraisals on the same axes makes the point directly. As the accounting boundary widens from farebox to the full social CBA, neither line moves much — and neither comes close to break-even. The entire difference between them is already present at the second step: demand.

The second chart places every published ratio for the two lines against the break-even line. Even the bus-based alternative to Navan — the cheapest option of all — only reaches 0.92. No option, on any growth or cost scenario in either appraisal, reaches 1.0.

6. What this means

1. The accounting boundary decides whether a case is arguable, not whether it passes. Analysis 1 is right that how wide you draw the boundary matters — it determines which benefits are even on the table. But for these two lines, widening it moves the ratio by only about 0.03–0.05. The boundary frames the debate; demand and cost settle it.
2. A BCR below 1.0 is normal for rail, and is not the end of the argument. Both lines "fail" the ratio, yet both appear in national strategy. That is because the ratio deliberately leaves things out — option value, long-run land-use and decarbonisation, and the political choice to rebalance regions — and because the framework loads costs (the 130% shadow price of public funds, 40% risk contingency) in ways critics argue are structurally hard on rail.
3. Demand is the lever that actually moves the number. Navan clears 0.68 at the direct-transport layer purely because its commuters save time against a congested road; the WRC cannot, because its train is no faster than the car. This is the same conclusion Analysis 3 reached from the demand side: the prize is dense, radial, time-competitive corridors.
4. Honesty about the ratios strengthens the case, it does not weaken it. Pretending the WRC "turns positive with wider benefits" (as this site previously implied) is both wrong and unnecessary. The accurate story — strong lines like Navan are near-misses held back mainly by cost, weak lines like the WRC are strategic choices — is more defensible and more useful.

Key figures & method

Both lines were appraised with social cost-benefit analysis under the Public Spending Code and the Common Appraisal Framework. BCR = present value of benefits ÷ present value of costs; break-even is 1.0. Shared and differing parameters:

Western Rail Corridor — cost sensitivity

Holding EY's benefits fixed at €77.2m (present value), the ratio responds only to very large cost reductions:

Navan line — published scenarios

The layer-by-layer figures are the author's arrangement of each appraisal's own published benefit categories; the running BCRs reconcile to the published all-in ratios (WRC 0.21, Navan 0.71). The WRC's wider-economic layer was assessed by EY as negligible and is shown as ≈0.

Data quality & limitations

• Official: all capital costs, present values, benefit categories, BCRs, NPVs and demand figures are taken directly from the EY (2020) and AECOM/NTA (2021) appraisals.
• Contested: the WRC's cost and demand assumptions are disputed by advocacy groups; the positive case is strategic, not a published BCR above 1.0.
• Modelled: the WRC cost-sensitivity figures are computed here from EY's fixed benefit total, not taken from the report.
• Not strictly comparable: EY used 2019 prices / 30-year horizon; AECOM used 2011 prices / 60-year horizon — compare the shape, not the last decimal.
• Dated / moving: AECOM's €777m–€1,122m is a 2021 estimate; the NTA has since indicated a figure toward €2–3bn (2024).

Sources

1. EY & Mott MacDonald — Western Rail Corridor: Financial and Economic Appraisal (for Iarnród Éireann), June 2020
2. TheJournal — Western Rail Corridor appraisal, reaction & advocacy response
3. West-on-Track — Western Rail Corridor campaign (advocacy; contests the cost and demand assumptions)
4. NTA / AECOM — Navan Rail Line Assessment Report, November 2021
5. Iarnród Éireann — Navan Rail Line, Emerging Preferred Route (34 km, four stations), 2026
6. RTÉ — Navan rail line Emerging Preferred Route published, May 2026
7. Irish Times — Navan–Dublin rail line likely to cost up to €3bn (NTA estimate), 4 Dec 2024
8. Oireachtas — Dáil written answer on the Navan rail business case, 16 Dec 2021
9. Department of Transport — Common Appraisal Framework (CAF) for Transport Projects and Programmes
10. Department of Public Expenditure & Reform — Public Spending Code
11. Transport Infrastructure Ireland — Project Appraisal Guidelines (PAGs)
12. gov.ie — All-Island Strategic Rail Review (AISRR), final report, 2024
13. NTA — Transport Appraisal Framework (2024 update)

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