Project Planning

The work before the work: quantity take-offs, cost estimating, project schedules, activity sequencing, and economic comparison of alternatives. It carries 4–6 of 80 questions on the WRE exam. The problems are short and the math is light, which makes them good points for anyone who reads the question twice.

What the problems look like

Mostly single-step, occasionally two. Recurring shapes — borrow-pit and stockpile volumes; cost-index escalation and crew-plus-equipment unit costs; estimate class by project definition; critical path and float on activity-on-arrow and activity-on-node networks, including crashing; precedence relationships (finish-to-start, start-to-start and the rest); earned value; and present worth, equivalent annual cost and benefit/cost comparisons.

By exam day you should be able to —

• take off volumes from a borrow-pit grid or a conical pile, in bank or loose measure;
• escalate a historical cost with a cost index and build a unit cost from crew and equipment rates;
• place an estimate in its class from the project's maturity;
• find the critical path, total and free float, and the cheapest way to crash a schedule;
• sequence activities with finish-to-start, start-to-start and finish-to-finish logic, including leads and lags;
• compute SPI and CPI and say what they mean;
• compare alternatives by present worth, EUAC, life-cycle cost and incremental B/C.

Where people lose points

• Borrow-pit grids: weight each corner by the number of grid squares that share it; answer in the measure asked (bank, not loose, unless the trucks are the question). A load factor of 0.75 is 33% swell, not 25%.
• Stockpiles: height comes from tan of the angle of repose, read from the row for the stated material and moisture.
• Escalation: scale by current ÷ historical index, applied to all items bought at the old date; unit costs need the whole crew and the rental at its own time basis.
• Scheduling: total float is late finish minus early finish — not free float and not a late-start date. Dummies carry logic even with zero duration. When crashing, watch for a second path turning critical and look first at activities shared by both paths.
• Earned value: SPI = BCWP/BCWS and CPI = BCWP/ACWP; below 1.0 means behind schedule or over budget. Invert either ratio and the conclusion flips.
• Economics: read the factor from the stated interest-rate table; a finite service life is not a perpetuity; credit salvage with (A/F) in an annual-cost comparison and with (P/F) in present worth; compare unequal lives on EUAC; escalation compounds.
• Mutually exclusive alternatives: rank by incremental ΔB/ΔC, not by the highest ratio, IRR or payback.

Have these at your fingertips

The interest-factor tables and their formulas, the network-scheduling relations, the earned-value indices, and the estimate-classification matrix — plus which of them the Handbook carries and where, so the lookup is fast and the right table is the one you open.

Going deeper

• Engineering economics
• A quarter of the WRE exam isn't water
• Project Sitework — the earthwork and equipment side of the same numbers

Part of the Water Resources & Environmental exam. Practice this area with exam-real problems — the tutor walks any one you miss. → Start practicing free — free with an account.