5.2 Schedule Compression, Resource Leveling, and Earned Value Cost Control

Once a baseline Critical Path Method (CPM) schedule and project budget are established, the project manager must actively control time, labor deployment, and jobsite expenditures. On the Tennessee Business and Law examination, candidates are tested on how to compress a delayed schedule at minimum cost, how to resolve trade crew over-allocations, and how to calculate Earned Value Management (EVM) metrics to detect cost overruns and schedule slippage before they become unrecoverable.

Schedule Compression: Crashing vs. Fast-Tracking

When a construction project faces an accelerated owner occupancy deadline, needs to recover days lost to unexcused delays, or seeks to avoid daily liquidated damages, the project manager must compress the schedule. The two fundamental schedule compression techniques are Crashing and Fast-Tracking.

1. Crashing (Time-Cost Tradeoff Analysis)

Crashing is the intentional compression of activity durations by allocating additional direct resources—such as authorizing overtime hours, adding a second shift, increasing crew size, or mobilizing higher-production equipment—to shorten the Critical Path. Because overtime premiums, shift differentials, and extra equipment rentals cost money, crashing always increases direct construction cost.

To compress a schedule economically, the project manager calculates the Crash Cost Slope (Crash Cost per Day Saved) for each crashable activity:

$$\text{Crash Cost per Day Saved} = \frac{\text{Crash Cost} - \text{Normal Cost}}{\text{Normal Duration} - \text{Crash Duration}}$$

When solving a schedule-crashing problem on the exam, apply three mandatory rules:

1. Never Crash a Non-Critical Activity: Crashing an activity that is not on the Critical Path wastes money because non-critical activities already have positive Total Float. Shortening a non-critical activity simply increases its float while reducing the total project duration by zero days.
2. Prioritize the Lowest Crash Cost per Day on the Critical Path: Among all activities currently on the Critical Path that have remaining crash capacity, always select the activity with the lowest Crash Cost per Day Saved first.
3. Monitor Parallel Paths Becoming Critical: As you shorten the Critical Path day by day, its total duration eventually drops until it equals the duration of a secondary path. At that point, both parallel paths are critical. Any further reduction in total project duration requires crashing an activity on both critical paths simultaneously (or crashing a single shared activity that sits on both paths).

Worked Numeric Example: Selecting the Optimal Activity to Crash

Suppose a project's current duration is 45 days, and the owner offers a bonus if the contractor compresses the schedule by 2 days (to 43 days). Review the four activities below:

• Step 1 (Eliminate Non-Critical Distractors): Even though Activity B has the lowest cost per day ($600/day), Activity B is not on the Critical Path ($\text{TF} = 5\text{ days}$). Crashing Activity B would save zero project days.
• Step 2 (Rank Critical Activities by Slope): Among the Critical Path activities (A at $1,500/day, C at $900/day, and D at $2,200/day), Activity C has the lowest crash cost slope at $900 per day and can be crashed by up to 4 days.
• Step 3 (Calculate Added Cost): Crashing Activity C by 2 days reduces the overall project duration from 45 days to 43 days for an incremental direct cost of $2 \times \text{\textdollar}900 = \text{\textdollar}1,800$.

2. Fast-Tracking

Fast-Tracking compresses a schedule by overlapping phases or activities that would normally be performed in strict sequential order—without necessarily adding overtime or extra crew labor. Fast-tracking is accomplished in two ways:

• Project-Level Fast-Tracking (Phased Design and Construction): Beginning site grading, deep foundations, and structural steel fabrication before the architect and engineers have completed 100% of the interior and mechanical construction drawings (common in Design-Build and CM-at-Risk delivery).
• Network-Level Fast-Tracking (Logic Overlapping): Rewriting network dependencies on the Critical Path so that sequential Finish-to-Start (FS) tasks become overlapping Start-to-Start (SS) tasks with leads (for example, starting rough plumbing and electrical in Zone 1 as soon as metal framing in Zone 1 is erected, rather than waiting for framing to finish across the entire floor).

While fast-tracking avoids upfront overtime expense, its primary drawback is substantially increased risk of coordination conflicts, design errors, and costly field rework if later design decisions conflict with foundations or rough-ins already installed.

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Resource Management: Resource Leveling vs. Resource Smoothing

Even when a CPM network is logically sound, plotting daily crew or equipment requirements on a Resource Histogram often reveals severe spikes—such as three concurrent activities requiring 18 masons on Tuesday and Wednesday when the contractor only employs 10 masons, followed by only 4 masons needed the following week. Schedulers address resource imbalances using Resource Leveling or Resource Smoothing:

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Job Cost Coding, S-Curves, and Earned Value Management (EVM)

Job Cost Coding and the Job Cost Ledger

Financial accounting tells a contractor whether the company as a whole made a profit last quarter, but job cost accounting tells the project manager whether a specific concrete or framing crew is losing money this week while corrective action is still possible. When a bid is won, the estimator's line items are converted into a project Job Cost Ledger organized by standardized Cost Codes (commonly structured around CSI MasterFormat divisions plus category suffixes for Labor, Materials, Equipment, and Subcontracts). Every field timecard, material invoice, and equipment rental ticket is coded to its exact work package so the project manager can compare budgeted unit costs and man-hours against actual field performance.

The Cumulative Construction S-Curve

When a project's cumulative budgeted cost (or cumulative man-hours) is plotted on the vertical axis against elapsed calendar time on the horizontal axis, the resulting baseline graph forms a characteristic S-Curve:

1. Early Mobilization Phase (Flat Lower Tail): During site layout, permitting, submittals, and initial excavation, only a small crew is on site and daily cash outflow is low, creating a gentle initial slope.
2. Peak Production Phase (Steep Middle Inflection): Once structural erection, building enclosure, and simultaneous mechanical, electrical, plumbing, and interior framing trades are working across the site, daily labor and material expenditures reach their maximum rate, causing the cumulative curve to climb steeply.
3. Closeout Phase (Flattening Upper Tail): During finish trim, startup testing, punch-list corrections, and demobilization, crew sizes drop sharply and cumulative expenditures plateau toward 100% of the Budget at Completion ($\text{BAC}$).

Earned Value Management (EVM) Formulas and Diagnostics

Comparing planned cumulative spending against actual cash spent is a dangerous trap: if a contractor planned to spend $400,000 by Month 4 and actually spent $360,000, the project looks $40,000 "under budget"—unless only $250,000 worth of physical work was actually installed! Earned Value Management (EVM) solves this problem by integrating scope, schedule, and cost through three core values:

• Planned Value ($\text{PV}$), or Budgeted Cost of Work Scheduled ($\text{BCWS}$): The authorized baseline budget for the work scheduled to be completed by the status date: $\text{PV} = \text{Planned \% Complete} \times \text{BAC}$
• Earned Value ($\text{EV}$), or Budgeted Cost of Work Performed ($\text{BCWP}$): The authorized baseline budget for the physical work actually completed in the field by the status date: $\text{EV} = \text{Actual \% Complete} \times \text{BAC}$
• Actual Cost ($\text{AC}$), or Actual Cost of Work Performed ($\text{ACWP}$): The actual dollars incurred on the job cost ledger to perform the work completed by the status date.

From $\text{PV}$, $\text{EV}$, and $\text{AC}$, four performance indicators and a completion forecast are calculated:

$$\text{Cost Variance (CV)} = \text{EV} - \text{AC} \qquad \text{Cost Performance Index (CPI)} = \frac{\text{EV}}{\text{AC}}$$ $$\text{Schedule Variance (SV)} = \text{EV} - \text{PV} \qquad \text{Schedule Performance Index (SPI)} = \frac{\text{EV}}{\text{PV}}$$ $$\text{Estimate at Completion (EAC)} = \frac{\text{BAC}}{\text{CPI}}$$

Worked Numeric Example: Complete EVM Project Diagnostic

A Tennessee commercial contractor has a total baseline budget ($\text{BAC}$) of $1,000,000 for a 10-month structural concrete package. At the end of Month 5:

• The baseline schedule called for 50% of the work to be completed: $\text{PV} = 0.50 \times \text{\textdollar}1,000,000 = \text{\textdollar}500,000$.
• Field quantity takeoffs confirm that 40% of the total concrete work is physically installed: $\text{EV} = 0.40 \times \text{\textdollar}1,000,000 = \text{\textdollar}400,000$.
• The job cost ledger shows $450,000 in actual labor, material, and equipment costs incurred to date: $\text{AC} = \text{\textdollar}450,000$.

Calculating the EVM metrics:

1. Cost Variance ($\text{CV}$): $\text{EV} - \text{AC} = \text{\textdollar}400,000 - \text{\textdollar}450,000 = -\text{\textdollar}50,000$ (Over Budget by $50,000).
2. Schedule Variance ($\text{SV}$): $\text{EV} - \text{PV} = \text{\textdollar}400,000 - \text{\textdollar}500,000 = -\text{\textdollar}100,000$ (Behind Schedule by $100,000 of work).
3. Cost Performance Index ($\text{CPI}$): $\frac{\text{EV}}{\text{AC}} = \frac{\text{\textdollar}400,000}{\text{\textdollar}450,000} \approx 0.889$ (Over Budget—earning only $0.89 of budgeted value for every $1.00 spent).
4. Schedule Performance Index ($\text{SPI}$): $\frac{\text{EV}}{\text{PV}} = \frac{\text{\textdollar}400,000}{\text{\textdollar}500,000} = 0.800$ (Behind Schedule—progressing at 80% of the planned rate).
5. Estimate at Completion ($\text{EAC}$): $\frac{\text{BAC}}{\text{CPI}} = \frac{\text{\textdollar}1,000,000}{0.8889} = \text{\textdollar}1,125,000$ (projected $125,000 total cost overrun at completion if crew efficiency does not improve).
6. Estimate to Complete ($\text{ETC}$) and Variance at Completion ($\text{VAC}$): The remaining cash needed to finish the job is $\text{ETC} = \text{EAC} - \text{AC} = \text{\textdollar}1,125,000 - \text{\textdollar}450,000 = \text{\textdollar}675,000$, and the forecasted final budget deficit is $\text{VAC} = \text{BAC} - \text{EAC} = \text{\textdollar}1,000,000 - \text{\textdollar}1,125,000 = -\text{\textdollar}125,000$.

The crashing example assumes one controlling path and linear crash costs over the proposed reduction. Recalculate all paths after each reduction; a second path can become critical, requiring more than one activity to be shortened. EAC = BAC/CPI assumes future cost efficiency remains like the measured period. CPI requires positive AC and SPI positive PV; equality means exactly on budget or schedule. Earned value percentages must be budget weighted when mixed work packages have different values.