Engineering Economics

Basic methods of engineering economics

Engineering economics compares alternatives by reducing their costs and benefits to a common, time-adjusted basis. The basic methods are:

1. Present Worth (PW) method — discount all cash flows to the present at the minimum attractive rate of return (MARR) and compare; choose the alternative with the highest net present worth.
2. Future Worth (FW) method — compound all cash flows to a common future date; equivalent to PW but used when the comparison date is at the end of the study period.
3. Annual Worth (AW) / Equivalent Uniform Annual Cost (EUAC) method — convert all cash flows into an equivalent uniform annual series; convenient for comparing alternatives with unequal lives.
4. Rate of Return (ROR / IRR) method — find the interest rate at which PW of benefits equals PW of costs; accept if IRR ≥ MARR.
5. Benefit–Cost Ratio (B/C) method — divide the present worth of benefits by the present worth of costs; accept if B/C ≥ 1. Mainly used for public projects.
6. Payback (Payout) period method — the time required for accumulated benefits to recover the initial investment; a simple screening tool, ignoring time value beyond the cut-off.
7. Replacement analysis — compares defender vs. challenger using EUAC or marginal cost to decide when to replace an asset.

Is cost–benefit analysis enough for every project? — My view

No. Cost–benefit analysis (CBA) is a powerful and necessary tool, but it is not sufficient for every project, for these reasons:

• Monetisation problem: Many benefits and costs — safety, health, environmental quality, social equity, national prestige — cannot be reliably converted into money. CBA then either ignores them or uses arbitrary shadow prices.
• Distributional effects ignored: CBA judges only aggregate net benefit. A project with a positive net benefit may still harm a particular group (e.g., displaced families in a hydropower or road project). Equity needs separate analysis.
• Uncertainty and risk: Future costs, traffic demand, interest rates and prices are uncertain. A single B/C ratio hides this; sensitivity, scenario and risk analysis are also required.
• Intangibles and strategic value: Projects such as rural telecom coverage, emergency communication or defence links may be justified on service obligation and national interest even when B/C < 1.
• Non-economic criteria: Technical feasibility, environmental impact (IEE/EIA), legal and regulatory compliance, and institutional capacity must be checked independently.
• Discount rate sensitivity: The choice of discount rate can reverse the ranking of alternatives, so results are not objective by themselves.

Conclusion: CBA should be used as the core economic test, but a sound appraisal combines it with financial analysis, EIA, social/equity analysis, risk and sensitivity analysis, and multi-criteria decision analysis. For a Nepal Telecom project, CBA must be supplemented by service-obligation and strategic considerations, since universal access in remote areas is a policy goal, not merely a profit calculation.