FAQs

1. Is Maclay Bridge in sound structural condition?

Yes, the Maclay Bridge Alliance (MBA) had Maclay Bridge inspected by a nationally renowned historic bridge engineer, Dr. Jai Kim, Prof. Emeritus at Bucknell University, and Robert Kim, PE. Their report is that Maclay Bridge is in good condition and certainly worthy of rehabilitation.

2. What advantages can be gained by rehabilitation of Maclay Bridge?

Dr. Kim provided MBA with five options for rehabilitation that could be designed and constructed around the existing bridge to retain its historic character. All options include strengthening the bridge with super-imposed arches. These concept plans range from the addition of a cantilevered walkway to expansion to a two-lane configuration. The preferred option would replace the two concrete trusses and the Warren Pony Truss on the east end of the bridge with a single reinforced Parker Truss span. Two intermediate piers on the east end would be removed thereby benefiting the health of the river while improving the appearance of the historic bridge. A cantilever pathway would be added to provide for pedestrian and bicycle users. The single-lane configuration would be preserved to provide the inherited rural traffic control which nearby residents value so greatly. Advantages are: a) cost; b) safety; and c) impacts on natural and human environments.

3. How would rehabilitation of Maclay Bridge improve vehicle accident statistics?

It will not improve due to the rehabilitation any more than construction of South Avenue Bridge will eliminate drivers under the influence. The motor vehicle accident rate at and near Maclay Bridge is high as compared to statewide rates, but cure must consider the contributing factors as well as the design aspects. County and state engineers attribute the cause to sharp curves and narrow roads. Consider that there have been no fatalities in a rural area where speeding is prevalent. That means everyone slows down for the single-lane bridge and the narrow roads to a less than lethal threshold for speed. Furthermore at least 40% of these accidents cite alcohol as a contributing factor, but cited factors have not included drugs.

The preferred solution by the county and MDT would widen the replacement bridge to two lanes, widen the approaches, and straighten the route from River Pines on to South Avenue. That means those drivers under the influence will no longer have to reduce speed as much as they travel through the area of higher residential density. Greater speed increases accident severity and the likelihood of a fatality, even if the accident rate is reduced. The answer to this dilemma is more law enforcement, not more expensive bridges and roads.

4. Is Maclay Bridge the site of frequent drownings?

Maclay Bridge has been the site of several drownings over the years. The most recent occurred near the bridge in August 2011. The bridge itself was only a reference location for that tragedy, it did not contribute to the accident. Prior to 2011, the Missoulian had recorded no drownings at the bridge for at least ten years. That was confirmed by Missoula Rural Fire Department call and response logs. All rivers in the Missoula area have drownings from time to time, but there is nothing to indicate Maclay Bridge has more than other nearby river reaches.

5. Has the proposed replacement, South Avenue Bridge complied with the National Environmental Policy Act and the Montana Environmental Policy Act (NEPA and MEPA)?

No! Missoula County and Montana Department of Transportation have pursued a Categorical Exclusion (CE) to these acts. To properly apply a CE to NEPA or MEPA requirements, there can be no significant impacts from the project that are not sufficiently mitigated.

An example of proper application of a CE would be the rehabilitation of an existing bridge that would not require new approach alignments. In our view, a CE could be properly applied to the rehabilitation of Maclay Bridge, but South Avenue Bridge requires a full Environmental Impact Statement to provide for identification and mitigation of its impacts.

6. Will the weight limit on a rehabed Maclay Bridge be increased for emergency vehicles and school buses?

Yes. The present weight limit of 11 tons could be increased to 36 tons. This increase is sufficient for the largest emergency vehicle in the rural fire department inventory, fully loaded.

7. If rehabilitated, what will be the useful life of Maclay Bridge?

The useful life will be extended by 40 years, the same as the design life for South Avenue Bridge.

8. Maclay Bridge has been deemed functionally obsolete. Will rehab change this status?

The term "functionally obsolete" is a designation based on scores for elements that make up the "sufficiency rating" for the bridge. The primary element contributing to this designation for Maclay Bridge is the single-lane when considered for the Average Daily Traffic count. The ADT peaked in 2010 at roughly 2600 vehicles per day, but it has since dropped to under 2000. Nevertheless the bridge does meet the criteria for the functionally obsolete designation and no contemplated rehabilitation is likely to change that.

A more important measure of functionality however is "wait time." The average time required to wait for opposing traffic when crossing the bridge. Wait time has typically been less than 30 seconds, even at peak usage days in 2010. Compare that to wait time at any controlled intersection on Reserve Street.

9. Maclay Bridge is "fracture critical." Does that alarming designation predict failure?

The term "fracture critical" is a term chosen by engineers to identify a bridge that lacks redundancy in its structural construction. Many new bridges constructed today are fracture critical and several of the optional plans for South Avenue bridge were fracture critical.

Our concept plan for rehabilitation of Maclay Bridge includes a strengthening arch imposed on the existing truss to add strength and redundancy to the bridge, thus eliminating the fracture critical designation.

10. Are there any examples near Missoula of bridges that exhibit the super-imposed arch structure to strengthen the bridge and add redundancy?

Yes! The Lucille Bridge over the Salmon River at Riggins, Idaho is a single-lane bridge much like Maclay Bridge. It has been rehabilitated to safely handle logging trucks. Other examples are railroad bridges on the Burlington-Northern Line near St. Regis. These bridges were all designed by Mr. Frank Muth, PE an engineer located right here in Missoula.

11. Please compare traffic calming for Maclay Bridge and for the proposed South Avenue Bridge.

As previously discussed, Maclay Bridge is a single-lane bridge that can only accommodate traffic in one direction. That configuration requires that approaching traffic from either side must approach with caution and be prepared to stop for opposing traffic already on the bridge. At times of high use, there may be as many as four or five vehicles opposing on the bridge or ready to follow on. Practical use allows vehicles to approach and follow leading cars that are less than halfway across. If more than halfway, and with opposing traffic waiting on the other side, courtesy requires that we stop to allow the opposing traffic to come forward. This technique works surprisingly well and only rarely do drivers abandon courtesy to jump in front of opposing traffic. Wait time is usually under 30 seconds.

The only traffic calming east of the bridge on North Avenue are stop signs at Humble and at Clements. West of the bridge, on River Pines, the road is quite narrow and lined by imposing trees and poles at the pavement's edge. These obstructions show remarkably little scaring from vehicles and their proximity to the traveled road obviously slows traffic. Though the speed limit is 35 MPH along River Pines, most traffic seems to travel under that speed, at least till they get to the slightly wider Big Flat or Blue Mountain Roads. MDT accident maps indicate the west end of the bridge and the first few hundred feet of River Pines exhibit the most accidents. Though overhead lighting and reflective traffic arrows were installed several years ago, neither the county nor MDT have compiled a report as to the effectiveness of these simple measures.

South Avenue Bridge as planned would be a two-lane structure with straightened alignments between the intersection of River Pines, Big Flat, and Blue Mountain Roads, and South Avenue. Engineers have recognized that the wider, straighter roads will lead to increased speed and have contemplated roundabouts, lane narrowing, and various other means of slowing traffic. A person can get a sense for how well this works by looking carefully at the new roundabout at South and 35th. It appears that traffic bounces over the curbs and across the base or over lawns with considerable frequency. Whether this is done as a result of DUI, inattention to driving, or simply someone that disrespects public property, the results are a preview of what could be expected at the South Avenue Bridge. 

 

©Maclay Bridge Alliance 2017
MBA • c/o Bob Schweitzer • 11905 Green Acres Road • Missoula, MT • 59804 • (406) 728-5302
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