I-75 Widening (MOT 75)

Approximately 140,000 vehicles squeeze through this subcorridor every day. During rush hour, traffic backups had caused major congestion, idling, and accidents. Merging across lanes to exit used to be nearly impossible, and bumper-to-bumper traffic jams pushed impatient drivers to side streets, causing unnecessary wear and tear on local roadways. Several left-hand entrance and exit ramps existed in this section, along with inadequate ramp spacing. In addition, drivers were often confused because there was only one continuous lane through downtown Dayton. To alleviate these problems, ODOT District 7 launched the $483 million I-75 Modernization Plan, a three-phase project to ensure smoother, safer traffic flow through the city while creating one primary ramp to access downtown Dayton.

With a total construction cost of $57.6 million, Phase 1b included the addition of one through-lane on I-75 and the complete replacement of the existing pavement of the 1.33-mile section of I-75 at the US 35 interchange, which provides three-lane continuity in both directions from just north of Edwin C. Moses Boulevard to just north of Fifth Street. This phase also included removing geometric deficiencies, replacing aging pavement, and updating entrance and exit ramps. The I-75 profile was lowered up to five feet. In addition, 13 new bridges were constructed along I-75 just south of the downtown area, seven bridges were rehabilitated, and three bridges were removed. The project also included relocation of an existing traffic signal at the intersection of Stewart Street and the southbound exit ramp from US 35, and the removal of two ramps at Albany Street.
Due to limited width on the ramp flyover bridges, it was not cost effective to maintain traffic on most of these ramp bridges while portions of the bridges were being reconstructed. Maintenance of traffic on the mainline bridges was particularly complex on the single bridge over three railroad tracks. The proposed improvements reconfigured this bridge into a combination of a precast arch structure and two bridges with embankments between.
American Structurepoint used an innovative approach to detouring ramp traffic for the first time in Ohio, utilizing a continuous flow turnaround (the Buckeye Turnaround), to detour ramp traffic while US 35 ramps are closed. The Buckeye Turnaround allowed US 35 ramp traffic to be diverted south on I-75, turn around under the Edwin C. Moses Bridge, and continue north on I-75 to their original destination. The turnaround was opened to traffic in September 2010. Approximately 4,000 vehicles per day (normal ramp traffic, 20 percent of the ramp) used the turnaround during construction, significantly reducing detour traffic on city streets.
The project also included the first Maintenance-of-Traffic Alternative Analysis prepared for a major ODOT project that is now included in ODOT’s Traffic Engineering Manual. This MOTAA analyzed three alternatives for I-75 traffic: crossover, part-width, and contra-flow. QUEWZ software was used to analyze potential backups and determine the impact of closures on traffic in order to develop a mitigation plan with alternate routes and appropriate detours. A hybrid of the contra-flow and crossover alternatives, which maintained two lanes of traffic in each direction on the mainline, was implemented. A third lane was added when a turnaround was in use. Seven bridges along I-75 were temporarily widened. Special provisions were also made to accommodate special events, particularly at the nearby University of Dayton.
Bridge work on Phase 1B included construction of 13 new bridges, rehabilitation of 7 bridges, and removal of 3 bridges. The new superstructures on the project included pre-stressed concrete beams, curved and dog-legged plate girders, and steel-rolled I-beams. Substructure work included new semi-integral and standard abutments on MSE wall-supported fill to eliminate many of the existing bridge end spans. In all, more than 2,000 feet of existing bridge length was eliminated with this project, for a substantial decrease in future bridge maintenance and a cleaner, more aesthetic-looking corridor.

At Cincinnati Street, the mainline bridge structures received new decks and were widened on different skews than the existing bridges to accommodate the geometrics and site distance on Cincinnati Street. There were single-span bridge replacements of 3-span structures over Stewart Street and Albany Street. The existing structures over US 35 have abutments and foundations integral with the flyover ramp structures' pier columns. The superstructures were replaced and the existing counterfort abutments widened to accommodate the new superstructure. The existing 9-span structure with hinged steel girders and beams spanning Washington Street and 3 railroad tracks was separated into 5 new structures with the use of over 1,000 linear feet of MSE wall. A 236-foot-long precast concrete arch with a 50-foot span was constructed on 25-foot-tall pedestal walls over the CSXT spur track.

For the structures over Edwin C. Moses Boulevard and Fifth Street, 3 existing bridge spans ranging from 65 to 100 feet were eliminated. "T"-type piers were utilized to cantilever the northbound widened structure over the intersection of Edwin C. Moses Boulevard and Fifth Street. To accommodate these roadways, the skews of the proposed structures varied from about 25 degrees to over 40 degrees in the opposite direction, and the spans varied from 25 to 125 feet.

Three of the I-75 and US 35 flyover ramp structures were modified, eliminating and replacing portions of the structures and constructing abutments on MSE embankment. MOT-35-1516N, in particular, is a 9-span, 1,198.5-foot-long structure spanning Norfolk Southern and CSXT tracks. The alignment of its "dog-legged" girder was revised to accommodate the widening of I-75. Two spans of the structure were replaced and 1 was eliminated. One end of the existing structure was previously supported at a hinge on another bridge. This hinge was eliminated, and the modified structure terminates at a MSE wall abutment.

One of the greatest challenges encountered by the project team was construction of the proposed bridges while maintaining traffic. There are only inches between the existing and proposed northbound and southbound structures, and several of the structures required part-width construction to accommodate traffic. Over 1,000 linear feet of temporary MSE wall, along with tied-back soldier pile and lagging, and sheet pile shoring was utilized to accommodate the tight construction. Aesthetic treatments on the proposed bridges and walls were coordinated with the City of Dayton and included the use of color, form liners, and aesthetic lighting.