Bus Depot Site Selection: Weighted Scoring With a Non-Compensatory Constraint
A transportation authority must select a site for a new bus depot. Three sites are scored on a 1–5 scale. Criteria and weights: capital cost 0.30, access to routes 0.25, environmental impact 0.20, schedule 0.15, community acceptance 0.10. Scores: Site A: cost 5, access 3, environment 2, schedule 4, community 2. Site B: cost 3, access 5, environment 3, schedule 3, community 4. Site C: cost 4, access 4, environment 4, schedule 5, community 3. A separate engineering review finds Site C lies within a 100-year floodplain; the authority's design standard prohibits permanent critical facilities there unless a $2.8M flood mitigation is added, which is not in the capital estimate. The budget is fixed and cannot absorb the mitigation without cutting service hours.
1. Calculate the weighted score for each site and identify the highest-scoring site. Show the arithmetic.
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Weighted score = Σ(weight × score).
A: 0.30×5 = 1.50; 0.25×3 = 0.75; 0.20×2 = 0.40; 0.15×4 = 0.60; 0.10×2 = 0.20; total = 3.45. B: 0.30×3 = 0.90; 0.25×5 = 1.25; 0.20×3 = 0.60; 0.15×3 = 0.45; 0.10×4 = 0.40; total = 3.60. C: 0.30×4 = 1.20; 0.25×4 = 1.00; 0.20×4 = 0.80; 0.15×5 = 0.75; 0.10×3 = 0.30; total = 4.05.
C has the highest weighted score, 0.45 above B and 0.60 above A. On the additive scoring model alone, C would be selected. The scores are ordinal judgments converted to numbers, so the 4.05 should not be treated as a precise measurement; it is a ranking device. The next step is to test whether any non-compensatory constraint eliminates C, because a high score on access and schedule cannot compensate for a prohibited site condition.
2. Apply the floodplain constraint. How does it affect the feasible set and the recommendation? What additional information would you request?
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The floodplain finding is a non-compensatory constraint, not just another criterion. The authority's standard prohibits a permanent critical facility in the 100-year floodplain unless $2.8M of mitigation is added. That mitigation is not in the capital estimate, and the fixed budget cannot absorb it without cutting service hours. Therefore C is not feasible as scored; its 4.05 is conditional on ignoring a must-have requirement. The feasible set is A and B, and B wins on weighted score, 3.60 versus 3.45.
Before recommending B, request: (1) confirmation that the floodplain boundary and the critical-facility definition apply to a bus depot; (2) a costed mitigation estimate and whether any grant or partner could fund it; (3) the schedule impact of mitigation, since C's schedule score of 5 may fall; (4) whether B's lower cost score reflects a real capital gap or a scoring judgment; (5) community-acceptance evidence for B, because A's low scores on environment and community suggest opposition risk. If mitigation can be funded externally, re-score C with the added cost and schedule and compare again.
3. Suppose the authority can fund the $2.8M mitigation without cutting service. Recalculate or reason about C's score and recommend how to proceed.
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If the mitigation is funded externally or from a separate resilience budget, C becomes feasible, but its cost score must reflect the added $2.8M. The original cost score of 4 was based on the capital estimate without mitigation. If the added cost moves C's cost score from 4 to 2, C's total becomes 0.30×2 = 0.60 + 1.00 + 0.80 + 0.75 + 0.30 = 3.45, tying A and below B. If the cost score falls to 1, C totals 3.15. If the mitigation also adds three months, its schedule score might fall from 5 to 3, reducing C by another 0.30. So C is no longer the clear winner once the constraint is priced.
Recommendation: run a revised scoring with the mitigation cost and schedule, and treat the flood risk as a residual risk even after mitigation. Do not simply add the mitigation as a separate line and keep the original cost score. Also check whether the $2.8M is a life-cycle cost or a capital cost, and whether it creates an ongoing maintenance obligation. If the revised C score is within about 0.10 of B, the decision should go to a sensitivity analysis or a deliberative review rather than being decided by the scoring arithmetic.