Questions · All waterways
How a lock queue works: arrival, precedence and cuts
First come, first locked, with three set exceptions. The typical commercial tow waited 33 minutes.
A lock queue works on arrival order. Federal rules say the vessel that reaches a lock first normally locks through first. Arrival is marked by posts or markers set above and below the lock, or by radio.
The exceptions
Three kinds of vessel jump the line. U.S. government vessels go first. Licensed passenger vessels on a published schedule or in the for-hire trade go ahead of cargo tows. Commercial cargo tows go ahead of recreational craft. Recreational boats are expedited by sharing the chamber with a tow when both agree. The lockmaster may change the order to make the best use of the lock, and a vessel that does not enter promptly when signalled loses its turn.
What the wait looks like
We measure the wait from a tow's arrival to the start of its lockage. Across 24,817 commercial lockages at 173 locks, the median wait was 33 minutes. 39% of tows started within 15 minutes. One in ten waited more than 6.7 hours, and 5% waited more than 12. Recreational and light craft had a median wait of about one minute.
Cuts: when a tow is longer than the chamber
A tow that does not fit the chamber goes through in pieces, called cuts. The first cut locks through and is tied off, then the chamber cycles back for the rest. 19% of commercial lockages in our archive, 4,821 tows, were split this way. Once a commercial tow starts, the chamber is busy for a median of 49 minutes, and one in ten takes more than two hours. Every one of those minutes is a minute the next tow in line waits.
Reading the live queue
Every lock page shows the Corps' count of tows waiting and its 4-hour average delay, refreshed every 15 minutes. Start with the Olmsted Locks and Dam page, or see why Kentucky Lock's waits run longest.
Sources: precedence and recreational lockage from 33 CFR 207.300(d)–(f), eCFR, retrieved 5 October 2026; lockages from the U.S. Army Corps of Engineers Lock Performance Monitoring System, archived by Lock Wait. Wait is measured from arrival to start of lockage; chamber time from start to end of lockage. How every number is defined.