IR 75 at Miamisburg-Springboro Pike/Austin Pike Interchange and the SR 741 at Miamisburg-Springboro Pike/Austin Pike Displaced Left Turn (DLT)
FHWA Definition: The Displaced Left Turn (DLT), formerly referred to as a Continuous Flow Intersection (CFI) is an alternative intersection design. The distinguishing feature of a DLT intersection is the relocation of the left-turn movement. The DLT intersection shifts left-turning vehicles to the left side of opposing traffic prior to the intersection, which consequently eliminates the left-turn phase for the approach at the main intersection. As such, DLT intersections offer several advantages compared to conventional signalized intersections for certain traffic conditions. Compared to a conventional intersection design, a DLT intersection design offers operational and safety benefits. Other benefits may include reductions in auto emissions and in travel time for selected movements in the DLT intersection.
DLT intersections offer improved operational performance compared to conventional intersections, particularly for relatively large left-turn and through volumes. The operational analysis conducted as part of this research and by others indicates that the operational benefits of the DLT intersection increase as traffic volume increases. Simultaneous movement of the left-turn and through traffic also improves progression of traffic platoons and increases vehicular throughput. Other operational improvements include reduced vehicle delay, reduced queue lengths, fewer stops, and increased capacity.
The subject project was constructed between May 2009 and October 2010.
Q: How much did the interchange at IR75, the DLT intersection, along with all the surface street improvements cost?
a: The total project construction cost = $40.6M.
Q: How much did the DLT cost in comparison to putting in a regular intersection?
a: According to the TID's estimate for MVRPC CMAQ application, the additional cost to build the DLT was $1,250,000 including additional R/W of $692,500.
Q: Who was the contractor on the project and when was it completed?
a: Prime Contractor was John R. Jurgensen, Co.
Q: Why did engineers put in a DLT and who made that decision?
a: Superior ability to handle left turns versus a conventional intersection, the decision to build a DLT was made between ODOT and local jurisdictions involved in the project. This was a collaborative decision-making process which also factored in the "conceptual" access management plan for the area.
Q: What is the issue at that intersection that causes the traffic to back up?
a: The northbound left turns and eastbound right turns are the movements that experience congestion and thus backups during AM and PM peak hours only. The overall traffic demand at the SR 741 and Austin Pike/Miamisburg-Springboro Road intersection, as well as additional intersections along both SR 741 and Miamisburg-Springboro Road/Austin Pike (including the IR 75 interchange ramps) have caused specific movements to back up at different times of the day.
Q: What movements are experiencing slowdowns?
a: The specific movements are the northbound to westbound left turns and the eastbound to southbound right turns during AM and PM peak hours only.
Q: What are some reasons for the increased traffic at that location?
a: Growth around the interchange and different land use than originally planned. The continuation of construction work at the interchange of IR 75 and SR 73 to the south.
Q: Did the original traffic counts underestimate traffic?
a: The original traffic projections underestimated two movements (northbound left and eastbound rights) at the intersection of Austin Boulevard and SR 741. Additional access points on Austin Boulevard have also affected traffic flow in the area.
Q: When was the original traffic study done for this project?
a: The Montgomery County Engineer hired DLZ/Wilbur-Smith in 1999. The original traffic study was completed in 2003.
Q: How far in advance are traffic studies typically completed prior to a major project?
a: It varies for a complex project or projects that affect the interstate, 10 years prior is not unusual. Other factors such as the ability to find financing also affect the timeline between an original study and the construction of a project.
Q: How much did the initial traffic study cost?
a: The original study which included the Major Investment Study, Interchange Justification Study, Environmental Overview, etc. was approximately $1,700,000. It should be understood the subject project was the preferred alternative resulting from this much larger study that examined existing conditions (traffic safety and operations, land use, etc.) in a study area in southern and western Montgomery County. This included the entire area for a new interchange location on IR 74 and other local roads improvements, such as Byer Road and Wood Road on the west. The DLT was not part of the overall study. That was determined during the design phase as with all traffic signal projects.
Q: Who was responsible for the original traffic study (who hired it done/what company conducted it)?
a: For the original study, Montgomery County held the contract which was executed by DLZ consultants. The decision to build the DLT was made during the subsequent Environmental Review (NEPA Process), the Montgomery County Transportation Improvement District (TID), held the environmental contract which was executed by LJB Consultants.
Q: How did engineers come to the decision to conduct an operational traffic study of the DLT?
a: Since opening day of the DLT, two movements were heavy; the northbound left turn and eastbound right turn. In order to analyze the movements and the operations of the DLT the recent traffic engineering study was completed. The traffic study also looked at the feasibility to improve the traffic flow. The decision was made because the traffic volumes were in some cases higher than anticipated and needed to be analyzed again for the entire network. This allowed ODOT to make changes immediately to the traffic signal timing along the entire corridor and to determine long term improvements.
Q: How much did the ME Companies DLT (CFI) traffic study cost?
Q: Who was responsible for the DLT (CFI) traffic study in early 2012 (who hired it done/what company conducted it)?
a: ODOT District 7 used its General Engineering Services design consultant, ME Companies to conduct the operational traffic study that was recently finalized.
Q: What issues if any did the operational traffic study find?
a: The study confirmed/quantified the poor level of service of the northbound left turn lane and eastbound right turn lane. The study reviewed building a single eastbound right turn slip lane and remove the signalized eastbound right movement, and to add a second northbound left turn lane (dual northbound left lanes). However, it did recommend the "No Build" at this time because the study unfolded additional concerns with building the dual northbound turn lanes. The primary concern is how will adding the dual northbound left turn lanes affect the IR 75 interchange; specifically, the IR 75 northbound ramp intersection.
Q: What are ODOT's plans to alleviate traffic issues at this location?
a: Currently, ODOT is planning to move forward with the design and construction of eastbound right turn slip lane to help reduce congestion for the PM commuter traffic back to the Springboro area.
Q: Who will pay for the adjustments or improvements at that location and how much will they cost?
a: The design will be an ODOT expense. Construction funding sources are still being identified by the district.
Q: Are there other DLT style intersections in the state of Ohio and if so, have they had similar issues?
a: There are no others in operation. However, ODOT District 8 has a DLT planned for an intersection in Hamilton County.
Q: What agencies are involved in the planning and decisions for this area (the DLT, IR 75 interchange, Byers Road, Austin)
a: Depending on the affected road and the type of funding involved many agencies could be involved in the decision making process including: FHWA, FAA ODOT, MVRPC, Montgomery County, Montgomery County Engineer, Montgomery County TID, Miami Township, City of Miamisburg, City of Springboro, and City of Dayton.
Q: What can drivers expect in the next two years at that intersection?
a: ODOT is committed to keeping traffic flowing, so we are constantly working on the traffic signal timing. We will pursue the construction of the eastbound right turn slip lane which will improve the operation of the overall intersection.
Q: Are there any issues at the IR 75 interchange itself?
a: No capacity issues. Slight traffic signal timing issues have been reported for the AM peak hour.
Q: What are the positive advantages of the new interchange and DLT intersection?
a: The main advantages observed at the DLT intersection was improved safety, increased capacity and reduced delay and travel time.
The new diamond interchange operates at an optimal level of service and has actually relieved congestion at several adjacent interchanges (IR 75 at SR 73, IR 75 at SR 725 and IR 675 at SR 725). A secondary benefit of the interchange is that it has spurred new economic development.