Vessel Sequencing In The Presence Of A Queue

1. Vessel Sequencing In The Presence Of A Queue Center For Transportation Studies University Of Missouri, St. LouisJune 15, 2005

2. Traffic Management Alternatives • Existing conditions: first come, first served with exceptions • Schedule appointments at locks • Using currently available information • Using additonal information (e.g. vessel tracking) • Re-sequence vessels in local lock queues • Re-sequence vessels in extended lock queues • Using currently available information • Using additonal information (e.g. vessel tracking) • Re-sequence vessels in multiple lock queues • Using currently available information • Using additonal information (e.g. vessel tracking) • System-wide traffic management using vessel tracking

3. Lockage Queues Causes • Dangerous conditions • Fog • High water • Fast currents • Accidents • Breakdown/malfunction of a lock • High demand

4. Queue Situation Responses • Given a set of vessels in queue at a given lock, in what order should the lockmaster clear the queue? • Currently a first come, first served protocol is used and occasionally modified by an N up/M down ordering. • What is the objective? Clear the queue ASAP according to some measure: • Time required to clear the queue or a weighted measure of total vessel delay times. • Possibly subject to a constraint on limiting the amount of time any particular vessel must wait in excess of a first come, first served processing time.

5. Factors Affecting Lockage Times • Upstream/downstream direction. • Single cut/double cut, jackknife, etc. • Experience and size of crew. • Use of motorized winches for recombining a double cut after lockage, helper boats. • Turnback/exchange set up times. • River Conditions (e.g. water levels, current, etc).

6. Reordering Of Vessels in a Queue (Case 1) • If all vessel combinations are of equal importance (tows with 1 barge are the “same” as tows with 15 barges), then we define the “weightings” of all vessels to be equal. • To minimize total waiting time of queued vessels we reorder the vessels on each side of the lock by the estimated shortest processing time (factors include upstream/downstream status, single cut/double cut, experience of crew, motorized winches, etc.) • Generally, this would mean single cuts are processed before double cuts, because they take less time to complete lockage.

7. Determining The Processing Order Through The Lock • Once the vessels are ranked using the weighting protocol, we determine the best lockage sequence considering the time required for a turnback or an exchange, and the upstream or downstream status of the previous vessel sent through the lock. After the reordering is completed, we then use an enumeration scheme to determine the up and down sequencing by considering the time required for a turnback or an exchange, and the upstream or downstream status of the previous vessel sent through the lock. • (Optional) one might also require than no vessel be delayed more than “D” hours over and above a first come, first served sequencing through the lock.

8. Reordering Of vessels In Presence Of A Queue (Case 2) • If all vessels are NOT of the same importance (tows with 1 barge are the “different” from tows with 15 barges), then we define the “weightings” to be different in general. • In such a case, we reorder vessels on each side of the lock by increasing values of (estimated lockage time/weight)

9. Reordering Of vessels In Presence Of A Queue (Case 2) (Continued) • Generally such an ordering would mean that double cuts with smaller estimated lockage times would be processed before double cuts with larger estimated lockage times and before single cuts (of a lower weighting).

10. Example • Assume weights are equal to the number of barges and the 3 vessels are on the same side of the lock • 15 barges with 105 minute lockage time • 15 barges with 90 minute lockage time • 3 barges with 45 minute lockage time • Then barges would be ordered by increasing value of lockage time/weight: • 90/15=6 min./Barge • 105/15=7min./Barge • 45/3=15 min/barge

11. Determine Processing Order Under A Weighting Protocol • Once the vessels are ranked using the weighting protocol, we determine the best lockage sequence considering the time required for a turnback or an exchange, and the upstream or downstream status of the previous vessel sent through the lock. • We are minimizing the weighted queue time over all possible orderings. • (Optional) one might also require that no vessel be delayed more than “D” hours over and above a first come, first served sequencing through the lock.

12. Consideration Of Tie-ups As A Queue Forms • Specify the nearest tie-up location on each side of a lock as a “buffer staging” area for the next vessel through the lock from that side. • If a vessel is initially tied-up in that location at the commencement of a queue situation, then it may be necessary to send that vessel through first, even though the weighting protocol shows a different processing order.

13. “Extended Queues” • Vessels enroute to a lock where a queue exists may be included in the complete enumeration as long as their estimated time of arrival at a lock is earlier than the estimated time of the first possible lockage of a vessel of similar characteristics. (The proposed vessel tracking system may be helpful in such a determination.)

14. Sequencing Vessels Systemically Through Multiple Locks • Such sequencing would appear to be problematic due to different upstream/downstream queuing situations at contiguous locks. • Another consideration is the “appearance” of additional vessels commencing travel in a given pool. • However, one can use the queue status (of adjacent locks) to determine initial order of vessels through the current lock.