A Comparison of takt time and LBMS planning methods

Takt time and LBMS are getting increased attention from practitioners of Lean Construction. The takt time approach focusses on designing work locations with similar quantities and plans on the same duration for each task without any buffers. To achieve level resource utilization takt time projects require substantial work backlog tasks or locations to absorb periods of low production demand. The LBMS approach plans on using consistent resources through all the locations. Buffers are added to absorb the risk of deviations and durations are allowed to vary based on quantity of work. This results in significantly longer schedules but decreases the need for workable backlog areas and the risk of demobilizations. To compare these two methods, three schedules planned with LBMS methodology were reformed into takt time schedules by forcing each task to have the same duration in each location. This was achieved by changing the crew size in each location to achieve a duration shorter than or equal to the takt time. The resulting schedules were compared in terms of total project duration, total project manhours and the risk of duration and manhours evaluated using Monte Carlo simulation. The results indicate that takt time achieves substantially shorter schedules but the manhours required in work backlog areas are much higher than in LBMS approach. In projects where quantities are similar between locations, takt time performs well if the resources are not demobilized when they run out of work. If the resources demobilize, the risk of return delays makes takt time a risky strategy.