Modeling dock doors

By defining a fixed number of dock doors (or loading docks), you can limit the number of vehicles that can load/unload shipments at the same time. In addition, you can define a minimum “reset time” between the end of a service operation for one vehicle and the beginning of the service operation for the next vehicle. This reset time is in addition to existing fixed and variable vehicle service times for loading and unloading. Docks doors can be defined for Sites and Customers.

Use the following columns on the Sites and Customers tables to define the dock doors:

• Number of Dock Doors – Specify the number of dock doors available at the location.
• Dock Door Reset Time – Specify the time required for the dock door after one vehicle leaves the door and the next one arrives at the same door. This time is in addition to the fixed and variable unloading and loading time at the stop. If you do not select a unit of measure, the default Time unit of measure from Model Settings is used.

You can use these fields to stagger the departure of vehicles, as often happens at a warehouse. If you do not define dock doors, there is no constraint on dock doors and multiple vehicles can be routed to the same location at the same time.

The solver includes a schedule shifting module to handle the dock doors constraint and ensure feasibility of the solution. Once a solution is found, route start times are delayed or advanced as necessary to respect the dock doors availability. If a route becomes infeasible (for example, if time windows are now violated), the route is destroyed and the shipments are added to the Unrouted Shipments table with the Reason “Unrouted due to dock door constraints”.

For example, assume that a warehouse has 10 dock doors. There is a Dock Door Reset Time of 30 minutes. Truck A is serviced at a dock door from 7:45AM to 8:30AM. It then leaves the DC at 8:30AM. The dock door can begin servicing the next truck at 9:00AM.

The Dock Door Assignment output table includes details about the dock doors assigned to the stops of each route.

Dock door notes

• For dock doors to be used, you must have non-zero loading and unloading times. You can define fixed/variable loading/unloading times (service times) on the Sites, Customers, and Transportation Assets tables. Where you define the service times depends on the behavior you require. For example, if a site services different types of Transportation Assets, use the service time columns on the asset to adjust the time at the dock.
• Dock doors act as hard constraints. You can use scenarios to adjust both the Number Of Dock Doors and Dock Door Reset Time to analyze use of these constraints.
• Dock doors are currently available for the following problem types:
  • standard optimization
  • interleaved optimization