2023 Engineering Excellence Awards, Honor Award Winner in the Special Projects Category awarded by the American Council of Engineering Companies (ACEC) of Iowa
Shortly after the High Trestle Trail Bridge over the Des Moines River was completed in 2011, the focus quickly shifted to continuing the trail south through the Ankeny community to link up with the Gay Lea Wilson and the Oralabor Gateway Trails on the south side of Oralabor Road. This vital linkage would also provide a direct trail route to Saylorville Lake and the expansive Neal Smith Trail. To make this final connection, the trail must traverse two busy roadways, Ankeny Boulevard and Oralabor Road. The Snyder & Associates team continued with their high-level trail planning and design work to develop plans for a pedestrian tunnel and bridge that would tie the trail network together. At the same time, the new amenities would incorporate design aesthetics that mimic the northerly trail sections and the High Trestle Trail Bridge between Madrid and Woodward.
Pedestrian Tunnel Under Ankeny Boulevard (US 69) Creates Safe Passage
From the Ankeny Market Pavilion near 1st Street, the High Trestle Trail cuts diagonally through town, following the old rail line the entire trail is situated on, passing near the Ankeny Police Station and Ankeny High School. At Ankeny Boulevard, our team explored options for carrying trail traffic over the busy roadway. The desired option was to build a cast-in-place RCB (box culvert) pedestrian tunnel under the street to create a safer and seamless path for bicyclists and pedestrians. Formliners were used to provide added detail and visual appeal to the tunnel's concrete walls, giving the appearance of large, cut stones at a fraction of the cost. Completed in two construction seasons, traffic signal upgrades, utility work, and minor grading were necessary to prepare the area for the tunnel construction. A gravity drainage stormwater system was designed for this location, negating the need for a pump station and resulting in substantial cost savings. Tunnel construction was completed with a multi-phased staging process to keep one lane of traffic moving in both directions at all times. The tunnel design included lighting, landscaping, and the ability to configure new or additional design elements in the future. Our team's plan also established the trail alignment to continue the trail from Magazine Road to Oralabor Road during the next construction phase.
Pedestrian Bridge over Oralabor Road "Book Ends" High Trestle Trail Bridge
The day after setting the bridge in place, contractors focused on paving the bridge approaches.
At the busy Oralabor Road location, the Gay Lea Wilson, Oralabor Gateway, and High Trestle Trails were brought together with an attractive pedestrian bridge over the roadway. Our team collaborated closely with city leaders to determine specific aesthetic details that would be included in the bridge. The Snyder & Associates team, in conjunction with the structural engineers from our subsidiary, Shuck-Britson, used an array of visualization tools and imagery to communicate detailed bridge designs and the relative costs needed to cover the construction. The design team pushed the boundaries of "typical" pedestrian bridge design to develop a unique structure worthy of its highly visible location. The preferred theme ultimately zeroed in on a design that would pay homage to the original bridge for which the trail is named, the 1912 High Trestle Bridge over the Des Moines River. This bridge was demolished and replaced in the 1970s to create Saylorville Reservoir. The former west abutment of that iconic bridge still stands and has been repurposed into an overlook of the new High Trestle Trail Bridge that replaced the railroad superstructure. The 1912 abutment has an interesting architecture that inspired the abutment frames on the bridge over Oralabor Road. Switchback sidewalks on either side of the roadway allow pedestrians and bicyclists to descend to the street level and access the Oralabor Gateway Trail. Or, after crossing the bridge, users can seamlessly continue south onto the Gay Lea Wilson Trail network.
Trail Connections Establish Central Iowa as an Outdoor Destination
With the completion of these two structures and the vital trail connections they create, central Iowa residents now have an incredible, interconnected array of trail options. It also has well-positioned the area as an outdoor enthusiast's vacation destination, drawing outside money for the local market. If the hundreds of residents who attended a recent grand-opening celebration for the new bridge are any indication, these new trail links will be popular attractions for many years.
