Phase VII · FE Civil Academy
Engineering Economics
Compare engineering alternatives on money and time, not opinion.
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Practical scenario
Two culvert alternatives have different first costs and maintenance streams over a 50-year life. Which is economically better at an 6% discount rate?
Why this matters
Every design recommendation ultimately competes on money over time. Economics items are formulaic and fast points if the factors are second nature.
Concept explanation
- Money has time value: a dollar today is worth more than a dollar later because it can earn interest.
- Interest factors convert between present worth (P), future worth (F), annual worth (A) and gradients (G).
- Alternatives are compared over equal service lives using present worth, annual worth, or rate of return.
- Benefit-cost ratio above 1.0 indicates an economically justified public project.
Unit guidance
- Write units on every substituted value.
- Cancel units symbolically before evaluating numbers.
- Confirm the result unit matches the quantity you were asked for.
Handbook navigation
- Open the Engineering Economics section of the handbook.
- Search the term "time value of money" rather than scrolling.
- Note the equation number so you can return to it quickly.
Calculator guidance
- Confirm angle mode before any trig entry.
- Store intermediate values in memory instead of re-keying rounded numbers.
- Round only at the final answer.
FE strategy
- Draw the cash-flow diagram before selecting a factor.
- Check whether the rate is per year or per compounding period.
Conceptual example
A conceptual engineering economics item will ask which quantity increases, decreases, or stays the same when one input changes. Reason from the governing relationship, not from memory of a numeric answer.
Common mistakes
- Mixing nominal and effective interest rates.
- Comparing alternatives over unequal lives without a common horizon.
- Placing the first annual payment at time zero instead of end of period one.
Guided practice
- Work the first worked example with the solution visible.
- Re-solve it closed-book and compare every step.
- Explain the unit cancellation out loud.
Independent practice
- Complete a 10-question Engineering Economics quiz in practice mode.
- Classify every miss by error category.
- Re-test the missed subtopic within 48 hours.
Summary
- Convert everything to one point in time before comparing.
- Equal service lives or annual worth for unequal lives.
- B/C > 1 justifies a public project.
Capstone application: Life-cycle cost and alternatives comparison in the Design Studio.