Improving an Outdated Corridor in Webster City
Initially constructed in 1930, US 20 is now known as East Second Street, a two-lane rural road, in Webster City. With the pavement in need of replacement, roadway geometry and clear zone out-of-date with current design standards, and a desire to construct an eight-foot sidewalk along the corridor, Webster City contracted Snyder & Associates in June of 2015 to lead improvement efforts.
Key considerations were focused on right-of-way (ROW) access and how to maintain traffic through the area during construction. To avoid any acquisitions and streamline the environmental process, the city wanted construction confined to the existing ROW. Multiple industries employing several hundred people just east of the project corridor, as well as four commercial businesses, a mobile home community, public dog park, cultural center, and 15 residential driveways within the corridor, required it to remain open to traffic.
Iowa’s First Project Use of Temporary Traffic Signals
To maintain traffic access during construction, Snyder & Associates reviewed alternatives for temporary lanes to maintain two-way traffic. All were deemed too expensive and/or would require additional grading outside the existing ROW. The use of temporary signals, pilot cars, and flaggers to maintain traffic was also considered, but would reduce the project into smaller segments, take longer to complete, and be more expensive.
Greg Karssen, PE, researched an innovative temporary, traffic signal. Placed at each driveway within the corridor, these portable signals can be synchronized with mainline temporary road signals to properly route driveway and side street traffic with east and westbound mainline traffic. When a driver exits a business or residence, the temporary driveway signal is activated and the direction of travel is selected. The green cycle of the temporary mainline signal is activated to merge driveway traffic into mainline traffic. Mainline temporary signals use radar detection to facilitate mainline traffic flow and are programmed to adjust the timing of the green cycle based on traffic volume.
The use of these signals allows one-lane, two-way traffic through the work zone without the need to construct a wide temporary pavement platform or use pilot cars or flaggers. Also, the distance between mainline signals is increased, which lengthens work segments allowing work to be completed more efficiently with fewer stages.
The East Second Street Improvement project was the first project in the state of Iowa suited for the implementation of individual, temporary traffic signals to direct the flow of traffic for property owners. The Iowa DOT had been interested in their use but didn’t have the right project suited for their use prior to East Second Street.
Additional Issues Resolved
Snyder & Associates also investigated issues concerning the existing water main within the project corridor, which had experienced 16 breaks in 13 years, and the existing sanitary sewer due to frequent blockages. It was discovered that corrosive soils within the project corridor were contributing to the water main breaks. Replacement and relocation of the water main to an area outside of the new paving and storm sewer were included with the project.
The sanitary sewer was found to have a several hundred foot stretch with little slope. Within this area, sewage flow was slowed and the water cooled, causing fats from two meat processing plants located upstream to coagulate and clog the line. As a result, thousands of dollars per year were spent to remove clogs. To improve flow and reduce maintenance costs, the sanitary sewer needs to be replaced and steepened.
All aspects of the project are slated for completion in fall of 2016.