1.5 Project Scheduling, CPM & Budget Management

Core Focus: Project success hinges on scheduling precision, phase-by-phase resource allocation, and rigorous cost engineering. Mastery of the Critical Path Method (CPM), float calculations, Earned Value Management (EVM), and tiered estimating methodologies is indispensable for LARE Section 1.

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1. Critical Path Method (CPM) Mechanics

The Critical Path Method (CPM) is an analytical, network-based scheduling technique used to determine the minimum total project duration, identify critical bottlenecks, and quantify scheduling flexibility (float) for every project task.

In landscape architecture, CPM networks are modeled using Activity-on-Node (AON) notation, where nodes represent activities with distinct durations, and arrows represent precedence dependencies (Finish-to-Start relationships).

The Forward Pass (Calculating Early Dates)

The forward pass determines the earliest possible calendar dates that activities can begin and conclude, moving left-to-right through the network:

1. Initial Activity: $\text{ES} = 0$ (or Day 1).
2. Early Finish Calculation: $\text{EF} = \text{ES} + \text{Duration}$
3. Successor Activities: When an activity depends on multiple predecessors, its Early Start is governed by the latest completing predecessor: $\text{ES}_{\text{successor}} = \max(\text{EF}_{\text{all predecessors}})$

The Backward Pass (Calculating Late Dates)

The backward pass determines the latest possible dates that activities can commence and finish without delaying the overall project completion deadline, moving right-to-left:

1. Terminal Activity: $\text{LF} = \text{EF}_{\text{terminal}}$ (the project completion duration).
2. Late Start Calculation: $\text{LS} = \text{LF} - \text{Duration}$
3. Predecessor Activities: When an activity precedes multiple successors, its Late Finish is governed by the earliest starting successor: $\text{LF}_{\text{predecessor}} = \min(\text{LS}_{\text{all successors}})$

Float (Slack) Calculations

Float represents scheduling flexibility. The LARE tests three specific forms of float:

Defining the Critical Path

• The Critical Path is the continuous sequence of dependent tasks through the network that possesses zero Total Float ($\text{TF} = 0$).
• It represents the longest duration path through the project network.
• Any delay to any activity on the critical path causes an identical, day-for-day delay to the overall project completion date.
• A network may possess multiple concurrent critical paths. Furthermore, if a non-critical activity with 5 days of total float is delayed by 8 days, the critical path will shift, making that activity critical!

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2. Scheduling Frameworks & Visual Tools

Work Breakdown Structure (WBS)

Before establishing a schedule, project managers develop a Work Breakdown Structure (WBS)—a hierarchical, deliverable-oriented decomposition of the total project scope.

• Hierarchy: Project $\longrightarrow$ Phase (e.g., Design Development) $\longrightarrow$ Sub-Phase / Work Package (e.g., Hardscape Detailing) $\longrightarrow$ Individual Task / Activity (e.g., Detail CIP Concrete Steps).
• The WBS establishes a coding structure (e.g., 1.3.2) used for resource allocation, fee tracking, and project accounting. It defines what is delivered, not the chronological sequence.

Gantt Charts vs. Network Diagrams

• Gantt Charts (Bar Charts): Display activities along a horizontal calendar timescale. Excellent for visual communication with clients, tracking percent completion, and viewing resource overlaps. However, standard Gantt charts do not clearly illustrate complex dependency networks or automatically highlight how a non-critical slip impacts downstream logic.
• Milestone Schedules: High-level executive summaries displaying major zero-duration achievement checkpoints (e.g., "50% DD Submittal," "Wetland Permit Approved," "Notice to Proceed," "Substantial Completion").

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3. Project Phases & Design Fee Allocations

Landscape architectural design fees are distributed across standardized phases developed to align with traditional Design-Bid-Build project delivery (e.g., AIA B101):

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4. Earned Value Management (EVM)

Earned Value Management (EVM) is an objective project performance measurement system that integrates scope, schedule, and cost metrics into a unified mathematical model. EVM answers three critical questions: Are we on schedule? Are we on budget? What is our true productivity?

The Core Triad

1. Planned Value (PV): The budgeted cost of work scheduled to be completed by a specific date: $\text{PV} = \text{Planned } \% \text{ Complete} \times \text{BAC}$ (BAC = Budget at Completion)
2. Earned Value (EV): The budgeted value of work actually completed: $\text{EV} = \text{Actual } \% \text{ Complete} \times \text{BAC}$
3. Actual Cost (AC): The total expenditures, internal direct labor, and costs incurred in completing the work to date.

Variance Formulas

• Schedule Variance (SV): $\text{SV} = \text{EV} - \text{PV}$
  • $\text{SV} > 0$: Ahead of schedule.
  • $\text{SV} < 0$: Behind schedule (work completed is less than planned).
  • $\text{SV} = 0$: Exactly on schedule.
• Cost Variance (CV): $\text{CV} = \text{EV} - \text{AC}$
  • $\text{CV} > 0$: Under budget (work accomplished cost less than budgeted).
  • $\text{CV} < 0$: Over budget (work accomplished cost more than budgeted).
  • $\text{CV} = 0$: Exactly on budget.

Performance Indices

• Schedule Performance Index (SPI): Measures schedule efficiency: $\text{SPI} = \frac{\text{EV}}{\text{PV}}$
  • $\text{SPI} > 1.0$: Work is progressing faster than scheduled.
  • $\text{SPI} < 1.0$: Work is progressing slower than scheduled.
• Cost Performance Index (CPI): Measures financial and labor efficiency: $\text{CPI} = \frac{\text{EV}}{\text{AC}}$
  • $\text{CPI} > 1.0$: Cost efficient; earning more value per dollar spent.
  • $\text{CPI} < 1.0$: Cost inefficient; spending more money than budgeted value created.

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5. Cost Estimating Across Project Phases

Cost estimating is not a single event; it is an iterative discipline whose level of detail and accuracy increases as design information matures.

Design Contingency vs. Construction Contingency

Candidates must strictly differentiate between these two budget reserves:

1. Design Contingency: An allowance established and controlled by the design team during the design phases (typically 15% to 20% in SD, reducing to 10% to 15% in DD, 5% in CD, and 0% at bid award). It accounts for evolving design details, unknown structural attachments, and unresolved code interpretations. As design details become finalized, the design contingency is steadily absorbed and eliminated.
2. Construction Contingency: A dedicated contingency fund (typically 5% to 10% of the bid amount) owned and controlled solely by the Owner during construction. It is reserved to cover unforeseen physical site conditions, concealed underground obstacles, contractor claims, and owner-requested scope modifications. The landscape architect cannot commit these funds without the owner's formal written Change Order.

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6. Real-World Case Scenario: The Collapsing Float

Scenario: During the construction of a 15-acre regional park, the installation of the main stormwater bioretention cell is scheduled as a non-critical activity with an Early Start on Day 40, Early Finish on Day 55, and Late Finish on Day 75 (Total Float = 20 days). The planting of the emergent wetland vegetation within the basin has an Early Start of Day 56. On Day 42, the earthwork contractor strikes an unmapped buried utility line, shutting down basin excavation for 18 calendar days while the utility company relocates the line. The contractor claims this delay entitles them to an immediate 18-day extension of the overall project completion date.

Analysis & Resolution: The landscape architect reviews the CPM baseline network. The bioretention cell possessed 20 days of Total Float. An 18-day delay consumes 18 days of float, leaving 2 days of remaining Total Float ($20 - 18 = 2$ days). Because the activity still possesses 2 days of float, the overall project completion date is not delayed. Therefore, the contractor's claim for a time extension to the project completion date is invalid. However, the 18-day delay consumed all Free Float ($FF = 56 - 55 = 1$ day), delaying the early start of the downstream planting subcontractor. The landscape architect must coordinate the successor tasks to ensure the new critical path does not slip past the remaining 2 days of float.

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7. Exam Traps & Pitfalls

1. Total Float vs. Free Float Confusion: Total Float delay affects the project completion date; Free Float delay affects only the immediate successor task. An activity can have zero Free Float while still having significant Total Float!
2. Design vs. Construction Contingency Misapplication: If an owner demands that an unexpected rock excavation claim during construction be paid from the "design contingency," the candidate must identify that the design contingency was already closed out at bidding, and the cost must be paid from the owner's construction contingency.
3. SPI / CPI Interpretation Errors: An SPI of 0.85 does not mean the project is 85% complete; it means the project is progressing at only 85% of its planned velocity (behind schedule). A CPI of 1.15 means the project is earning $1.15 of value for every $1.00 spent (under budget).
4. CD Phase Fee Proportion: Candidates frequently underestimate the Construction Documents phase fee allocation. CD is the largest phase (35-40%), far surpassing Schematic Design (15-20%) or Design Development (20-25%).