Members of the Washington Bridge Enhancement Committee gave engineers a clear direction this week on architectural design and visual aesthetics to consider in moving forward with the bridge design.
Two structure options were presented Wednesday, both girder systems with no overhead truss, as had been decided at an earlier meeting. Each option could be re-striped for three lanes.
“If we do need to relieve congestion before we would build the future fourth lane, if it was needed, it would be expandable to three lanes with shoulders,” said Judy Wagner, MoDOT area engineer.
After discussion, the committee voted 4 to 3 to move forward with a variable depth girder superstructure, which means the side girders, as seen from a distance, would range from 18 feet deep at the piers to 10 feet at the midpoint between piers.
The option is about $2.2 million more expensive than a parallel option, which is what the bridge in Hermann has. Because the girder is structural, MoDOT will pay for either the variable depth or parallel girder.
The parallel option was about $46.5 million and the variable depth was estimated at $48.5 million.
Fred Gottemoeller, an architect with Bridgescapes, said the variable depth girder uses materials more efficiently, but must be specially fabricated which adds to the cost.
The bridge is slated to have two 12-foot lanes, two 10-foot shoulders and a 10-foot-wide bike path.
A traffic count shows about 11,000 vehicles cross the span each day. In 20 years, that number is expected to increase to 17,000 vehicles per day.
General traffic guideline from the Manual of Uniform Traffic Control Devices indicate that a bridge must have 36,000 vehicles cross per day (18,000 each direction) to require four lanes.
With a 1 percent increase in traffic each year over the next 20 years, it would take 100 years before a fourth lane was needed.
At 2 percent growth per year, which is higher than average, it would still take 50 years, said Kevin Kriete, HDR architect.
Growth for the past six years has averaged 1.25 percent each year, he said.
Because of the traffic count, Kriete said, it would be better to build the bridge with the possibility of a third lane with no changes, and the possibility to add a fourth lane when and if it’s needed.
Committee members at first were concerned that the design wouldn’t allow for expansion to four lanes.
Engineers assured committee members that all options will be expandable in the future and several options for expansion would be available.
Committee members said growth has continued west and many factors contribute to traffic, including that the economy has been down over the past several years.
Bill Halmich, bridge committee member, said it would be a mistake to build a bridge that’s supposed to last 75 to 100 years with data spanning 20 years.
“This bridge will be expandable,” Wagner said. “We’ll add another two girder lines to the east, which is where the existing structure is today.”
Wagner said it’s possible that the fourth lane won’t be needed for another 75 years. Meanwhile, the substructure could be sitting there, rotting, and would have cost $5 million — because at that time, a new substructure or new bridge would be needed.
Using initial estimates, the substructure also would be visible and not as aesthetically pleasing for the next 50 to 75 years.
Cory Imhoff, HDR engineer, said the original plan to expand with one girder line is not feasible, but other options would allow for expansion.
“All we’re saying is that when you put in the superstructure (in the future) you will have to widen the substructure as well,” he said. “It’s just a matter of how it’s got to be done and what makes sense. Our substructure and superstructure will be able to integrate with it.”
The committee also discussed pier enhancements, overhead pier enhancements and the possibility of a pocket park to fill the void where the old bridge abutment is now.
The number of overlooks and possible locations also were discussed.
The committee originally had discussed two overlooks, which would be located on the piers on both sides of the main river channel.
There is a possibility for two overlooks, but, because of the placement of the piers, which is where the overlooks would be, one overlook wouldn’t be visible from the riverfront.
The committee will discuss only having one overlook, as well as having two, but with both on piers that are more centered on the river and more visible from the riverfront, which would be more “architecturally appealing.”
The committee has expressed interest in overhead signage and will look at rendering and options at the next meeting.
Committee members also agreed that a pocket park could be incorporated into the design, but would be considered as a future add-on and not in the initial construction.