Retired Temple U. Prof. Howard Weiss is the developer of the POM and Excel OM software that we provide free with our text.
On March 26, 2024 the container ship Dali crashed into the Francis Scott Key Bridge that spans Baltimore harbor. Ships had crashed into major bridges previously but in this case the damage was far worse than usual. The bridge collapsed into the harbor, 6 died, and, of course, travel across the harbor was affected.
The Dali was not even that large, with a capacity of 10,000 containers. (The largest container ships have a capacity of 24,000 containers). The obvious operational problem is that the bridge, which carried over 30,000 vehicles daily could not be used and the vehicles had to take either alternative routes. Reconstruction of the bridge began in January, 2025 but the detours will be needed until Fall, 2028.
The NTSB reported that Maryland did not conduct a test that would have identified structural risks for the bridge. After this incident, the NTSB indicated that 68 bridges that have commercial traffic in the U.S. needed to be inspected.
A recent study provided a list of the 20 bridges with the highest probability of having major damage due to being hit by a ship. The results of the top and bottom five in that list are displayed below along with reliability calculations in the shaded area.
The table performs these computations for each of the 20 bridges for a 1- year period, a 10-year period and a 100-year period.
The single year reliability is simply = # of years minus 1 divided by # of years. For example, for the Huey P. Long Bridge, reliability is 16/17 = .9412. That is, there is roughly a 6% chance of an accident in any given year. From your Heizer/Render/Munson textbook (Ch. 17), the 10 year reliability is given by
Rs=R 1 ×R 2 ×R 3 ×…× R 10
And since the reliability each year is the same this is identical to R 1 ^10. Thus, there is roughly a 50% chance that in 10 years the Huey P. Long bridge will have an incident. The safest of the 20 bridges, the John Blatnik has a less than 1% chance of a major accident over 10 years. Similar computations are given for a 100 year period.
Classroom Discussion Questions
1. What actions can be taken to reduce the chance of a major accident?
2. If the number of years between collisions can be increased by 10% (rounded up) how does that affect the 10 year reliability for the Long and Blatnik bridges?
