Delivering a work earlier can reduce permanence costs, free up resources and help you meet a committed date. To decide how much to speed up, you need to relate the time recovered to the cost of achieving it. KOSAN incorporates the functionality of Schedule crashing to evaluate that decision from the construction schedule and the resources of your budget.
This guide explains what schedule crashing is, how to calculate it, and how to interpret its results with examples. The figures are didactic exercises prepared for this article: they do not represent market prices, works executed or savings guaranteed by KOSAN.
What is schedule crashing in cost engineering?
The schedule crashing is a program compression technique that seeks to advance completion through additional resources in activities that determine the deadline. It may involve more labor crews, equipment, or available work time. The planned scope is preserved and the incremental cost of accelerating is evaluated. PMI: Pressed for time.
In terms of costs, the central question is how much the direct cost increases and what expenses or benefits the new delivery date changes. This balance between acceleration cost and deadline-dependent costs is studied in the time-cost analysis. PMI: Linear programming, an approach to critical path management.
Why it matters and what it is for
The schedule crashing allows you to prepare an acceleration proposal with explicit quantities and resources. It is useful when negotiating an early delivery, recovering part of a delay or comparing alternatives before committing more personnel and machinery.
For the cost engineer, the result can become a concrete decision: how much additional budget to request, what activities to intervene in, and what estimated savings the proposal supports. It also allows us to distinguish between the fastest date and the most economically convenient date; both can be different.
For example, if an alternative requires additional $13,000 but avoids $20,000 of expenses that are effectively time-dependent, the estimated balance is favorable at $7,000. If you demand $19,000 to avoid $24,000, there is still a savings of $5,000, but it is less convenient than the first. We will develop both scenarios later.
The critical path determines where to accelerate
An activity can finish earlier without modifying the delivery of the project. To compress the deadline, critical activities must be reviewed and the network recalculated after each change. When parallel critical paths appear, it may be necessary to accelerate several activities together. PMI: Crash with confidence.
In practice, it also reviews obligatory dates, supplier deliveries and work area-end restrictions. Adding staff to an activity awaiting authorization or supply can increase spending without advancing the next job. The network and data must reflect actual running conditions.
How to do a schedule crashing analysis
The basic procedure combines program logic with cost acceleration options: define activities and precedence, identify critical path, estimate incremental costs, choose a feasible reduction, and recalculate the deadline. PMI: Crash with confidence.
To convert it into a work proposal, prepare the following:
- A reliable starting program. Confirm quantities, durations, calendar and relationships between activities.
- Concrete options ahead. Defines which labor crew, team or additional shift could work and when they would be available.
- A complete incremental cost. It includes the supports required by the alternative: incorporation of personnel, supervision, lighting or mobilization, when appropriate.
- A comparison with the actual deadline. Check how much the project delivery is advanced, as well as how much each activity is reduced.
- A proposal to execute and control. Registers assumptions, responsible parties and authorized resources; Then compare the observed durations and costs with the estimates.
Consistency between activities, resources, calendar and tracking is part of good programming practices. PMI: Practice Standard for Scheduling, Second Edition.
Cost per day of activity duration reduction
For an exercise with a linear relationship between duration and cost, the time-cost slope is used:
Incremental cost per day = (accelerated cost − normal cost) ÷ (normal duration − accelerated duration).
It is an approximation between two known alternatives; It does not assume that any level of acceleration is technically possible. Time-cost models can also distinguish sections with different slopes. PMI: Linear programming, an approach to critical path management.
If an activity costs $40,000 on 8 days and $44,000 on 6 days, the increase is $4,000 to reduce 2 days: $2,000 per reduced day of that activity. Before taking it as the cost per day in advance of the project, check the effect on all the routes that determine its completion.
Example 1: shorten a sequence of activities
Let's consider three consecutive activities: A → B → C. All amounts are in Mexican pesos and VAT is omitted. We will use a continuous calendar just to simplify the exercise, so one day reduced in the sequence is equivalent to one day less deadline. In a real project, the date change must be calculated with your work calendar.
We assume linear costs within the limits of the table, available resources, and no additional constraints. The activities and their amounts are hypothetical.
| Activity | Normal duration | Minimum duration | Normal cost | Minimum cost | Increase per day reduced |
|---|---|---|---|---|---|
| A. Excavation and preparation | 10 days | 7 days | $50,000 | $59,000 | $3,000 |
| B. Foundation assembly | 8 days | 6 days | $40,000 | $44,000 | $2,000 |
| C. Forming and casting preparation | 6 days | 5 days | $30,000 | $36,000 | $6,000 |
The normal period is 10 + 8 + 6 = 24 days and the initial direct cost is $120,000. The complete sequence is critical because activities are executed one after another.
Objective: go from 24 to 21 days
In this network, B offers the lowest cost per day. Reduced from 8 to 6 days for an additional $4,000. A is then reduced from 10 to 9 days for an additional $3,000.
The new deadline is 9 + 6 + 6 = 21 days. 3 days advance and direct cost increases $7,000, until $127,000.
Now suppose that the work has $4,000 per day of avoidable overhead by finishing earlier. The estimated savings for those 3 days is 3 × $4,000 = $12,000. The net cost of overtaking is $7,000 − $12,000 = −$5,000: Under these assumptions, the total cost decreases $5,000.
Objective: find the preferred project duration
Let's compare different alternatives with the same data:
| Term | Direct increase | Resulting Direct cost | Overhead to $4,000 per day | Total cost considered |
|---|---|---|---|---|
| 24 days, normal program | $0 | $120,000 | $96,000 | $216,000 |
| 21 days, reduction of B and part of A | $7,000 | $127,000 | $84,000 | $211,000 |
| 19 days, maximum reduction of A and B | $13,000 | $133,000 | $76,000 | $209,000 |
| 18 days, maximum reduction of A, B and C | $19,000 | $139,000 | $72,000 | $211,000 |
With these conditions, 19 days is the lowest cost term among all combinations of integer durations allowed in the fiscal year. A is reduced to 7 days, B to 6 and C remains at 6. The savings compared to the normal program is $216,000 − $209,000 = $7,000.
To reach 18 days you must also reduce C. That last day costs $6,000 and only avoids $4,000 from overhead: it increases the total cost $2,000 compared to the alternative of 19 days. Still, it could be chosen if there is a mandatory date or sufficient additional benefit. That benefit would have to be documented and added to the comparison.
Example 2: two critical paths change the decision
Now let's assume two parallel routes that start from the same start and converge at delivery: route P of 20 days and route Q of 18 days. They do not share activities. In this exercise, each route has a reducible activity: P's costs $1,500 per reduced day and Q's, $2,500.
By reducing P by two days, both routes remain at 18. Delivery goes from 20 to 18 days and the direct increase is 2 × $1,500 = $3,000.
To finish in 17 days you must reduce an additional day on each route. The increase of that new step is $1,500 + $2,500 = $4,000. If you only reduce P to 17, Q still requires 18 days and delivery remains on day 18.
Let us now assume avoidable overhead of $3,000 per day. The first reduction of 2 days avoids $6,000 and costs $3,000: improves the balance by $3,000. Moving from 18 to 17 days avoids $3,000, but costs $4,000: it worsens that balance by $1,000.
The example shows why the cost of the combination needed to advance delivery. If multiple routes share a driving activity, accelerating that activity could jointly reduce them; Separate interventions are not always necessary. PMI: Crash with confidence.
Which overhead costs and benefits should you consider?
A reduction in lead time can lower total cost when the additional expense of speeding up is offset by lower time-dependent costs. The result depends on the rate and the execution alternatives considered. PMI: Managing risks in projects with decision technologies.
Review each game. The duration of some supervision or a rent that is billed per day can be reduced by ending early. An already committed monthly rental, a pay-per-event facility, or a fixed cost can stay the same. Capture only the spending you would really avoid and retains the support of the estimate.
The same applies to delivery bonuses, customer retention costs or avoided penalties: check their conditions and avoid counting the same benefit twice. Keep the comparison with the same scope and cost criteria for all alternatives.
How KOSAN supports schedule crashing analysis
KOSAN connects the acceleration analysis with the construction schedule and with the unit price analyses resources of the budget. That relationship allows you to study early delivery with a cost base linked to your project.
The functionality allows you to establish a delivery date or a deadline in calendar days and evaluate delivery options. more labor crews, overtime and second shift, depending on the available settings. It presents the activities that are shortened, the proposed way of executing them and the estimated extra cost per activity.
The result brings together four pieces of information to compare alternatives: Direct cost overrun, Savings by term, Net cost of advancing and New direct cost dear. You can also adjust the overhead savings per day and other early delivery benefits.
To use with a consistent base:
- Review your budget and the unit price analysess, and link the program activities to the line items they execute.
- Confirms the schedule, durations and relationships of the project program.
- Open Schedule crashing from the program and establish the date or period you want to evaluate.
- Check in Fine adjustments the acceleration options, consumption factors and productivity rates, supports and overhead applicable to your work.
- Compare the proposed activities and the economic balance; confirms in the field that there are resources and fronts available.
- If you decide to apply the alternative, incorporate compression into the program. The tool allows you to return to the original durations and dates you modified, preserving subsequent changes made by hand.
The analysis shows a new estimated direct cost; Applying compression to the program does not automatically rewrite the budget. Use the result to review and authorize the resources and costs that you will actually incorporate into the execution.
In KOSAN, the balance by term uses calendar days. To transfer an exercise like the previous ones, first verify the difference between the delivery dates obtained with the calendar of your work; Do not replace that difference with the sum of days reduced in activities.
Schedule crashing and fast-tracking: two ways to compress a schedule
The schedule crashing evaluates additional resources to reduce durations. The fast tracking overlaps jobs that were planned in sequence. The second option requires reviewing technical relationships and the risk of rework. PMI: Pressed for time.
For example, adding a labor crew to a face with available space can be part of the schedule crashing. Starting an activity before finishing its predecessor modifies the sequence and requires another evaluation. Do not confuse this modification with the cost of increasing resources on the same work area.
Choose a completion date with schedule and cost in view
A well-planned schedule crashing analysis ends with a verifiable proposal: new date, intervened activities, necessary resources, additional cost and expenses that would be avoided. Subsequent monitoring allows checking whether the planned consumption and productivity ratess are met and correcting the execution.
With KOSAN you can evaluate how much it costs to advance delivery and compare that cost to the savings per term within the same budget and schedule environment. Before committing to a date, use its Schedule crashing functionality to build and review your alternative.