Memorandum

City of Lawrence

Public Works

 

TO:

Charles Soules, P.E., Director of Public Works

 

FROM:

David P. Cronin, P.E., City Engineer

 

CC:

Mark Thiel, Assistant Public Works Director

 

Date:

August 5, 2013

 

RE:

Project PW1135 - 6th & Iowa Geometric Improvements

Update on Project Status and Schedule

 

 

Project Description

The primary scope of the 6th & Iowa project has been to include a dedicated left turn lane for west bound traffic. The proposed left turn lane will reduce the average intersection delay, reduce accidents and improve traffic flow in a significant way.

 

The dedicated left turn lane can be established by widening the roadway to the north and reducing the width of the existing lanes from 12 feet to 11 feet. Sidewalk on the north side will be reconstructed and the existing guard rails on both north and south side of 6th street will be replaced with a combination of concrete safety barrier and new guard rails. Additional improvements include an eastbound right turn lane, new sidewalk on the south side of 6th Street to Rockledge and new traffic signal equipment.  Pavement in the intersection will be milled and overlaid as the base is generally in good condition.

 

The attached general layout sheet shows a plan view of the proposed improvements and traffic lane configuration.

 

Project Status

The intersection widening project was originally scheduled to begin construction in spring 2013 however some design challenges have postponed the start of the project.  The original design extended the existing headwalls of the box bridges vertically a couple feet to hold the additional fill required to widen the roadway.  A preliminary structural review of this design and the concern of modifying the existing boxes yielded KDOT's recommendation to seek an alternate design.  The second design option included steepening the slopes with permanent erosion control and possibly using soil ties/anchors on the slope/wing walls for boxes.  After geotechnical investigation of this option it was determined that the slopes could not be increased greater than the current condition and maintain an acceptable factor of safety.  Finally, the plans were revised to include the only feasible option for widening 6th Street, the extension of both box structures ten feet to the north.  The box extensions will allow 6th Street to be widened to the north and provide back slope tie-ins equal to existing.  Plans are now complete and under review by staff and KDOT.

 

Project Schedule

The extension of the box structures will necessitate the closure of McDonald Drive underneath 6th Street and increase the construction time of the project.  The expected closure of McDonald Drive would be 1-2 months and traffic would be detoured to Rockledge Road.  With the timing of such a closure, staff recommends delaying the start of the project until spring 2014. Both box structures are maintained by KDOT. Currently, the boxes need some repairs and KDOT is looking into performing a maintenance project to rehabilitate joints that have spalled out inside the boxes.  A possible maintenance project would be put together by KDOT this fall and construction would coincide with the road closure for the extension, so the boxes will only be closed one time. To make the repairs, KDOT may access the top of the structures by digging through 6th Street. It should be noted that although the boxes were built in the late 50's, they have a life expectancy of 75 years and are structurally in good condition.

 

Project Funding

The original design and construction costs were estimated at $900,000 to be funded with General Obligation (GO) bonds. The additional design and construction costs are now estimated to be $1,440,900.  This project is included in the KDOT turnback agreement for 6th Street (US40) from Iowa to K-10.  Per the agreement, KDOT will allocate $1,500,000 for improvements at 6th & Iowa.