CVEN9702 Chap.4 Resource Levelling and Constrained Scheduling
Resource Levelling and Constrained Scheduling
Resource histograms aggregate activity demand across time and expose overloads, valleys and workforce instability. Resource levelling moves flexible work to smooth demand while protecting completion where possible. Resource-constrained scheduling starts from a hard capacity limit and may extend the project.
Priority rules guide choices, but every proposed sequence must still respect precedence and be tested for its actual completion result.
What this chapter covers
- 01
Build a resource histogram from scheduled activities
- 02
Distinguish smoothing from hard-cap scheduling
- 03
Use free float before consuming downstream flexibility
- 04
Apply and explain a resource priority rule
- 05
Recalculate duration and criticality after each move
- 06
Compare crew continuity, cost and completion outcomes
Worked example · free
Schedule four activities with five workers
- +1A and B cannot overlap because their combined demand is seven, above the five-worker cap.
- +1Run A from day zero to three, then start B and C together using exactly five workers.
- +1B and C both finish at day five, after which D runs from day five to nine.
- +1Testing B first gives a longer finish because four-worker D blocks four-worker A.
- +1Choose the A-first sequence and report a feasible project duration of nine days.
Key terms
- Resource histogram
- A column profile showing total demand for a resource over the scheduled project duration.
- Resource levelling
- Movement of activities within available flexibility to reduce peaks, valleys and workforce instability.
- Resource-constrained schedule
- A feasible schedule produced under a fixed limit that may extend completion beyond the unconstrained network.
- Priority rule
- A stated heuristic used to choose among eligible activities when resources cannot support all of them.
- Crew continuity
- The stability of workforce deployment without avoidable hiring, firing, idle periods or repeated mobilisation.
Resource Levelling and Constrained Scheduling FAQ
What is the difference between levelling and constrained scheduling?
Levelling seeks a smoother demand profile and often uses float to preserve completion. Constrained scheduling obeys a hard resource cap and may extend the project. State which objective applies before judging whether a move is successful.
Which resource priority rule is always best?
None. Earliest late start, shortest duration and largest resource use each have a rationale, but the resulting schedule must be tested. A heuristic guides the choice; it does not prove the shortest feasible project duration.
Can a resource move change the critical path?
Yes. Delaying an activity beyond float can extend its path and make it critical. Shared-resource constraints can also create controlling sequences that do not appear in an unconstrained network, so recalculate criticality after rescheduling.
Why compare more than one priority rule?
A heuristic gives a repeatable choice, not proof of optimality. Compare feasible sequences by completion, peak demand, idle capacity and mobilisation effects before recommending one.
Exam move
Take a small network and add one resource quantity to every activity. Draw the early-start histogram and identify both capacity breaches and inefficient valleys. First move an activity inside free float and confirm that successors and project finish stay unchanged. Next impose a hard crew cap and build a schedule event by event: list eligible work, choose a stated priority, check combined demand and advance to the next finish.
Compare at least one alternative sequence rather than assuming the first heuristic is optimal. Report maximum resource use, project duration and any major hiring or firing changes. Finally, redraw the network or logic table to identify the new controlling sequence. In written answers, distinguish the schedule objective from the commercial recommendation.
A smoother profile can still be costly if it delays completion, and a short schedule can still be impractical if it requires impossible mobilisation or congestion. Use a decision-time worksheet with columns for eligible activities, remaining durations, resource demand, priority value and capacity left. Advance time only to the next activity finish or resource release; do not make arbitrary daily choices when nothing changes.
Practise at least three priority rules, such as minimum total float, shortest duration and earliest late finish, on the same network. A heuristic gives a repeatable choice, not proof of optimality, so compare final duration and idle capacity. Mark any activity delayed solely by the capacity limit and trace the new resource-constrained controlling sequence.
Then distinguish levelling from allocation: levelling seeks a smoother profile within available flexibility, whereas constrained scheduling must respect a hard ceiling and may extend completion. Add mobilisation, congestion and skill compatibility to a second pass because identical headcounts do not guarantee interchangeable crews.
Quantify the consequence of each proposal with peak demand, workforce variation, project finish and any critical milestone movement. If overtime or subcontracting is suggested, name the cost, productivity and safety assumptions. Finish by checking that every scheduled start still respects network precedence.
This disciplined audit prevents an attractive histogram from becoming an infeasible programme and turns the numerical result into a defensible operational recommendation.
