How Many Dock Positions Do I Need?
One of the most important facility requirements for any logistics operation is the amount of dock high positions an industrial building provides. Often overlooked, dock high positions can have a significant impact on whether an operation is able to meet its key performance indicator objectives and contribute to the overall success of a company.
Determining the minimum number of dock positions needed for a facility involves an understanding of the internal and external factors which affect the amount of dock high positions required. The internal factors can include the amount of trucks serviced by the docks over a period of time (average and peak), the time to load and unload each trailer per dock, staging and cross-docking requirements, work hours over a period of time, employee breaks, drop trailer requirements, trash / bailing requirements, shifts, and shipping preferences.
External factors can include time of truck arrivals and departures, the reliability of carriers, whether carriers will back haul drop trailers, types of trailers used by carriers, and truck driver capabilities. A comprehensive understanding of these and any other internal and external factors will result in more precise understandings of an operation's dock high requirements.
In general, the minimum number of dock high positions are calculated based upon a formula involving their use, the amount of time they can be used, and a safety factor. Below are three examples of manual calculations using some of the internal and external factors above.
Number of Truck Positions Needed = ((Number of Trucks per Year x Hours it takes to Load / Unload a Truck) / Work Hours per Year) x Safety Factor [1]
Inputs
7,000 trucks per year
2.5 hours for loading / unloading
2080 work hours per year
Safety factor of 25%
Calculation
(7,000 trucks per year x 2.5 hours for loading / unloading) / 2080 work hours per year) = 8.4 x 1.25 safety factor = 10.5 docks or 11 dock high positions needed at a minimum
Number of Truck Positions Needed = Number of Trucks per Hour x Turnaround Time per Hour [2]
Inputs
20 trucks per day
8 hour work day
150 minute turnaround time
Calculation
(20 trucks per day / 8 hour work day) = 2.5 trucks per hour x (150 minute turnaround time / 60 minutes per hour = 2.5 turnaround time) = 6.25 dock positions needed or 7 positions needed
If all trucks arrive in AM, then work day would be shortened to 4 hours and the dock requirements would be 12.5 or 13 positions needed
((Peak trucks per day) x (Average dock time per truck) x (Safety factor of 1.5 to 2)) / Number of hours in work day [3]
Inputs
20 trucks per day
2.5 hours per truck
8 hour work day
Calculation
((20 trucks per day) x (2.5 hours per truck) x (1.5 safety factor)) / 8 hour work day = 9.375 docks required or 10 docks needed
These three calculations show that depending on the formula used, roughly the same inputs will yield slightly to drastically different minimum dock requirements. Where formulas 1 and 3 resulted in 11 and 10 positions required, formula 2 resulted in only 7. Not surprisingly, formula 2 did not employ a safety factor. Safety factors are used to account for unforeseen variability such as disruptions in deliveries or labor.
Companies may also employ manual simulations of dock requirements. These simulations include the detailed logging of docks used by the various types of vehicles that deliver or ship to a facility. These simulations can show how to improve dock assignments or delivery schedules for better dock utilization and determining of minimum docks required.[4]
The use of technology in determining the minimum number of dock positions required may make the use of the manual calculations above obsolete. Warehouse management systems or WMS may include dock requirements based upon much more detailed inputs and trends. However, the manual calculations formulas above help to show the importance of understanding the external and internal factors involved with determining the minimum number of dock positions for a given operation.
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[1] Mulcahy, David E. Warehouse Distribution and Operations Handbook. New York: McGraw-Hill, 1994. 4.18-.20. Print.
[2] 4Front Engineered Solutions, Inc. "Dock Planning Standards." (n.d.): 10. Web. 31 July 2016.
[3] Gross & Associates. "Calculating Dock Door Requirements." (n.d.): n. pag. Web. 31 July 2016.
[4] Mulcahy, David E. Warehouse Distribution and Operations Handbook. New York: McGraw-Hill, 1994. 4.18-.20. Print.
