The Difference Between Resource Leveling and Resource Smoothing

This knowledge point is the core of resource optimization techniques in project management, often used to solve problems of resource allocation conflicts.

I. Problem Description and Core Concepts

Before project execution, we estimate the resources (e.g., personnel, equipment) and duration required for each activity and generate a preliminary project schedule. However, this initial plan may have a problem: excessive fluctuation in resource demand. For example, requiring 10 engineers in one week but only 2 in the next. This "roller coaster" type of resource demand brings many issues:

• High Costs: May require temporary hiring or firing of personnel, generating additional costs.
• Management Difficulties: Alternating periods of resource idleness and overutilization affect team morale and work efficiency.
• Infeasibility: Resource demand may exceed the company's actual supply capacity.

To solve this problem, project managers use two important resource optimization techniques: Resource Leveling and Resource Smoothing. Their common goal is to make resource usage as uniform as possible, but their implementation methods and applicable scenarios differ significantly.

II. Solution Process: Gradual Understanding

We can understand through a simple analogy: imagine you are a head chef in a kitchen, needing to arrange chefs to complete various dishes (project activities) for a large meal. The number of chefs (resources) is fixed.

Step 1: Understanding the Constraint – The Project Critical Path

• Key Point: Any adjustment to the schedule must not ignore the "critical path." The critical path is the longest sequence of activities in the project, determining the shortest total project duration. Delaying any activity on the critical path directly delays the entire project.
• In our analogy: Some dishes must be made in sequence (e.g., soup must be simmered before seasoning). These are the dishes on the "critical path," and their timing determines how quickly guests can eat.

Step 2: Understanding the First Technique – Resource Leveling

1. Goal: To solve the problem of resource over-allocation, where resource demand exceeds availability. This is a problem that must be resolved.
2. Core Question: "In my plan, I need 5 chefs at the same time, but I only have 3. What should I do?"
3. Operation Process:
   • Identify Conflict: First, analyze the resource histogram to find the "peak" periods where resource demand exceeds availability.
   • Adjustment Strategy: Resolve the conflict by delaying the start of non-critical activities, typically using the activity's Total Float (Total Slack).
   • Key Impact: Resource Leveling usually leads to an extension of the final project duration. Because to wait for resources to become available, we have to postpone some activities to start later, which may affect the critical path.
4. Back to the Analogy: You find that the activities "stir-frying" and "grilling steak" are scheduled for the same time, requiring 4 chefs in total, but you only have 3. This is impossible. So, you check the schedule and find that "grilling steak" has some flexibility (it's not on the critical path). You can postpone it until after "stir-frying" is complete. This way, you only need 3 chefs to work sequentially, but the consequence is that the "grilling steak" will be served later, potentially delaying the entire meal's end time (project duration).

Step 3: Understanding the Second Technique – Resource Smoothing

1. Goal: To make resource demand as uniform as possible without changing the total project duration. It addresses the "volatility" of resource demand, not "over-allocation."
2. Core Question: "In my plan, resource usage is feasible, but I need 5 chefs in the first week and only 1 in the second week. This fluctuation is too large. Can it be made smoother?"
3. Operation Process:
   • Constraint: Resource Smoothing has a rigid constraint – it cannot change the project's critical path and total duration.
   • Adjustment Strategy: It can only use the activity's Free Float (Free Slack) for fine-tuning. Free Float is the amount of time an activity can be delayed without delaying the early start of any of its immediate successors.
   • Key Impact: Resource Smoothing does not change the total duration. It only slightly shifts activities forward or backward within the allowed time frame to "level the peaks and fill the valleys," making the resource histogram look smoother.
4. Back to the Analogy: The guests' meal time (total project duration) is fixed. You find the chefs' workload is heavy at the beginning and light later. So, you decide to move some preparatory work (e.g., vegetable cutting and preparation, an activity with free float) from later to slightly earlier, making the chefs' workload more balanced throughout the meal preparation period. But you would never alter the sequence or timing of those critical dishes (activities on the critical path).

Step 4: Summary, Comparison, and Decision

Now, we can clearly compare the two:

Summarizing the problem-solving approach:

1. First, check if your schedule has resource over-allocation (demand exceeds limits).
2. If it exists, you must use Resource Leveling to solve the problem by adjusting activities (potentially affecting the critical path) and accept the possible extension of the duration.
3. After resource demand becomes feasible, if you feel resource utilization fluctuates too much and want further optimization, then use Resource Smoothing to make the resource chart more aesthetic and efficient without touching the critical path.