The most cited benefit of location-based management systems has been a reliable schedule compression of 10-20%.  However, in my opinion, even more important is the capability of location-based management to decrease the risk of the project.  Location-based management decreases the risk of the project in many ways:

-- explicit assumptions

-- continuous production

-- formula-driven forecasting; no "wishful thinking"

-- verification of the estimate through the schedule

 

Explicit Assumptions

CPM schedules record durations and dependencies. Only the person who planned the schedule is able to understand where logic and durations came from and what assumptions are included in the durations. LBMS makes everything explicit. Durations are functions of quantity, productivity, and the number of resources.  Anyone who challenges a duration needs to challenge one of these components.  In CPM, durations cannot be challenged because any duration is right!  You can choose any duration if you staff for it.  However, if the assumptions are not explicit, it is very difficult to actually manage to that duration.

 

Continuous Production

Planning continuous workflow is a realistic model of production.  Subcontractors need to work continuously to maximize their productivity.  If continuous work is not planned in project schedule, subcontractors may legitimately refuse to come to the site because "there is not enough work ahead of them."  If a subcontractor runs out of work and has to demobilize, they will generally not come back immediately when some work is available.  Superintendents realize that return delays are typically between one and two weeks.  If the activity is on a path with float less than 2 weeks, the return delay will, in fact, make the path critical!  This is the main reason why traditional CPM methods do not work and why critical path tends to fluctuate from path to path.  CPM schedules have no way of enforcing continuous workflow and thus are unrealistic models of production.  (For more information on the different between location-based flowline schedules and CPM, please view the archived BIM 401 webinar on model-based scheduling.)

 

In contrast, location-based scheduling forces the planner to make a decision whether a task will be performed continuously or discontinuously.  Continuous work does not increase project duration if production rates of predecessors and successors are aligned.  Additionally, subcontractors typically can perform work much faster and with more quality if they know that they will not be interrupted.  These factors decrease the risk of return delays and thus the risk level of the project.

 

Formula-Driven Forecasting

Forecasting with location-based schedules uses the actual production rate achieved to-date and projects that to upcoming locations and similar types of work performed by the same subcontractor.  The key difference to traditional CPM techniques is that the forecast duration of upcoming locations of similar work is adjusted.  CPM only adjusts the remaining duration of started locations but keeps the upcoming task durations constant.  The typical way of planning control actions to restore the schedule is to decrease the durations of upcoming activities on the critical path.  This is wishful thinking.  Original durations did not have any assumptions related to manpower, quantity, or productivity.  Therefore, changing the durations of upcoming activities will not require a change in any such assumption.  Effectively, CPM planners are cheating both themselves and the Owner.  Because durations are typically decreased in the end of the schedule, this approach leads to huge hurry, overtime work, and cost escalation in the last two months of the project when it is impossible to continue cheating.

 

Location-based schedules recognize that a small delay will morph into a large delay if something is not done now.  Location-based management systems promote early warnings and early reaction.  LBMS requires a change in underlying assumptions - something real must be done to adjust manpower or productivity.  In a large project, it is extremely risky to wait until the last two months to catch up.

 

Verification of the Estimate through Scheduling

In LBMS, the project estimate is used directly in scheduling.  The schedule is an estimate tied to time.  Typically this reveals severe errors in the estimate.  LBMS calculates durations by using the model-based quantity, the estimated productivity rate, and the optimized crew size.  Quantities are objective because they come from the model.  Productivity rates come from the estimate.  Crew size is a choice to synchronize and optimize production rates of preceding and succeeding tasks.  Superintendents typically know how large a crew a particular task needs.  If the required crew size is too large or too small, either the quantity is wrong, or the estimate is wrong, or the superintendent is wrong.  These discrepancies initiate fact-finding which typically reveals that someone on the project team is not on the same page.  The early resolution of these conflicts and the reconciliation of assumptions decrease the risk level of the project.

 

If you'd like to learn more about how the estimator and scheduler work together, we offer a step-by-step guide to our 5D virtual construction workflow with video tutorials. These videos are just 2-5 minutes in length, but illustrate how to use a particular piece of functionality. You can access the video library index and view just what you need, or download the complete set of training videos. We have training videos for Estimators, Schedulers, Supers, and anyone who does CM Reporting.