Vessel Sequencing In The
Presence Of A Queue
Center For Transportation Studies
University Of Missouri, St. Louis
June 15, 2005
Traffic Management
Alternatives
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Existing conditions: first come, first served with exceptions
Schedule appointments at locks
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Using currently available information
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Using additonal information (e.g. vessel tracking)
Re-sequence vessels in local lock queues
Re-sequence vessels in extended lock queues
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Using currently available information
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Using additonal information (e.g. vessel tracking)
Re-sequence vessels in multiple lock queues
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Using currently available information
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Using additonal information (e.g. vessel tracking)
System-wide traffic management using vessel tracking
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Lockage Queues Causes
 Dangerous conditions
- Fog
- High water
- Fast currents
 Accidents
 Breakdown/malfunction of a lock
 High demand
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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.
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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).
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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.
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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.
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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)
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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).
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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
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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.
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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.
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“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.)
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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.
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