Queue and Transit Times

Use this supporting function to specify and maintain queue and transit times. These times are used when calculating lead times for manufactured products. Positive values increase lead time and negative values reduce it. A negative queue or transit time indicates overlapping operations.

Queue and transit times are applied when material leaves a work center, not when it arrives at the next one. Transit time is defined at the work center from which the material departs and represents the delay after an operation finishes, before the next operation can start.

If a delay must occur before the next step, you must define it on the previous operation. Think of it as a forklift picking up material from a work center. Transit time is the period required for the material to leave one work center and be delivered to the next. This time is scheduled at the departure work center, not at the destination.

Outcome

Queue and transit times are specified for further processing, such as calculating product lead times.

Before you start

You must meet these requirements before you use this supporting function:

Work centers are entered in 'Work Center. Open' (PDS010).
All work centers have a value specified in 'Queue unit' field.

See Work Center.

Follow these steps

This supporting function includes these activities:

Maintain parameters for queue and transit times

Parameters for queue and transit times are maintained in 'Work with Queue and Transit Times' (PDS020). This program is accessed from 'Work Center. Open' (PDS010) using Related option 13 = 'Queue/Transportation Time'.

See Maintain Parameters for Queue and Transit Times.

Additionally, the names of the three constants used throughout the queue and transit timetable are defined on (PDS020/P). These constants act as logical placeholders representing fixed points in the production flow. The names defined here are what appear as START, END, and ALL in the transit time records.

This table shows the constants along with their respective values and purposes:


Field	Default value	Purpose
Constant 1	DFTSTR	Defines the name used for the START constant. Represents the point before the first operation.
Constant 2	DFTEND	Defines the name used for the END constant. Represents the point after the last operation.
Constant 3	DFTTME	Defines the name used for the ALL constant. The fallback for inter-operation transit.

These names are configurable, and you can change them to match your organization's naming conventions. However, all transit time records must use the same names consistently. If you rename a constant, any existing records that use the old name will no longer be recognized by the scheduler.

The P panel displays the current transit time value stored for each constant, with a blank 'To - Work Center' field representing the system-wide default for each category.

Specify queue and transit times
Queue and transit times are entered in (PDS020). This is called from the menu or from (PDS010) using Related option 13 = 'Queue/Transportation Time'.

See Enter Queue and Transit Times.

Queue and transit times alternatives

Transit time accounts for the period between when material leaves the From - Work Center and when work begins at the To - Work Center. The transit value is always regulated by the From - Work Center's queue unit, unless a constant is involved, in which case it is always in days.

If a material moves from one work center to another and the product structure consists of the these operations:

Op 10 to Group 1
Op 20 to Group 2
Op 30 to Group 3: This is the last operation.

Transit Time Selection

The system first checks whether a specific transit time is defined between the two work centers. If no specific transit time is found, it checks for a general rule. If neither is defined, no transit time is applied.

This table shows all possible transit time records and indicates when the scheduling engine applies each one:


From - Work Center	To - Work Center	When the scheduler uses this record	Queue value regulated by
Group 1	Group 2	Transit between Op 10 and Op 20. This is direct pair and highest priority.	Queue unit for Group 1
Group 2	Group 3	Transit between Op 20 and Op 30. This is direct pair and highest priority.	Queue unit for Group 2
Group 1	ALL	Fallback transit when material leaves Group 1 and no direct pair to the next work center exists.	Queue unit for Group 1
Group 1	END	Transit time after the last operation until the product is available.	Queue unit for Group 3
START	Group 1	Transit time before the first operation, which is Group 1. This is the time from material availability until work begins.	Always days
ALL	Group 1	The scheduler applies this record as a fallback transit when material leaves Group 1 and neither a direct pair nor a Group 1 to ALL record exists.	Always days
START	blank	The scheduler applies this record to define the general time before the first operation when no specific START-to-first work center record exists.	Always days
END	blank	The scheduler applies this record to define the general time after the last operation when no specific last work center-to-END record exists.	Always days
ALL	blank	The scheduler applies this record as the ultimate fallback when no specific pair, no direct-to-ALL, and no ALL-to-group record exists.	Always days

Lookup priority

This table shows the how the scheduler searches between two consecutive operations:


Priority	Lookup	Example
1st	Direct pair	Group 1 to Group 2
2nd	From work center to ALL	Group 1 to ALL
3rd	ALL to From work center	ALL to Group 1
4th	ALL to blank	ALL to blank
None found	Zero transit time assumed	n/a

This table shows the how the scheduler searches before the first operation:


Priority	Lookup
1st	START to Group 1
2nd	START to blank
None found	Zero transit time

This table shows the how the scheduler searches after the last operation:


Priority	Lookup
1st	Group 3 to END or END to Group 3
2nd	END to blank
None found	Zero transit time

This table shows common scheduling mistakes and their correct setup:


Mistake	Reason	Correct setup
ALL to Group 3: Adding transit before arriving at Group 3.	ALL resolves against the work center the material is leaving. This record defines transit when leaving Group 3, not before arriving there.	Use these records to correctly define transit and safety times in the schedule: Define Group 2 to Group 3: This is a direct pair ALL to Group 2: This serves as the default transit when leaving Group 2.
ALL to `<last work center>`: Expecting post-production safety time.	The ALL constant is for inter-operation transit, not post-production time.	Group 3 to END: Define this record to specify post-production time after the last operation.
START to Blank and END to Blank: Defining only these records without specific work center.	This entry makes it the lowest‑priority fallback. The scheduler checks specific records first, and these apply only if nothing else matches.	To provide the scheduler with specific records for the first and last operations, configure these entries: START to Group 1: Define this record for the first operation. Group 3 to END: Define this record for the last operation. Tip: Keep the blank versions as a safety net.