Share

Share link

https://www.msconsultants.com/new-interchange-roundabout-and-bridge-replacement-boost-safety-ease-congestion/

New Interchange, Roundabout and Bridge Replacement Boost Safety, Ease Congestion

ms consultants, inc.

February 1, 2021

Southern Mahoning County has experienced significant residential and commercial growth, placing high-traffic demands on inadequate local roadways. This has led to an increase in traffic congestion and crashes at the I-680 interchange with Western Reserve Road/SR 164. Concurrently, the portion of I-680 between Western Reserve Road  and the Ohio Turnpike was significantly underused, essentially functioning as a long ramp to and from the turnpike toll plaza. This led Eastgate Regional Council of Governments (Eastgate) to explore adding a new interchange at the SR 164 overpass two miles farther south, thereby encouraging more local traffic to use I-680 and relieving congestion at Western Reserve Road.

 

Study Phase: Alleviate Traffic Congestion, Improve Safety

 

Eastgate, in cooperation with the Ohio Department of Transportation (ODOT), hired ms consultants, inc. (ms), to study and evaluate traffic congestion and safety problems within the southern I-680 corridor. The study involved:

  • Assessing construction of a new interchange at I-680/SR 164 to alleviate traffic demands on Western Reserve Road by encouraging more vehicles to stay on I-680
  • Considering parallel routes within the corridor to better use I-680 south of Western Reserve Road
  • Identifying alternatives to improve commuter safety

 

Subsequent to ms’s study phase, ODOT continued the Interchange Justification study, including further study of high crash rates at I-164/SR 626. Results of the study revealed that the crash rates could be mitigated by installing a roundabout, widening the SR 164 bridge over the Ohio Turnpike and improving the SR 626 intersection. ODOT retained Johnson, Mirmiran & Thompson (JMT) to design these project elements.

 

Design Phase

 

Based on the results of ms’s study, the team designed and prepared construction plans for a new I-680/SR 164 interchange, including full-access ramps. Additionally, ms provided:

  • Management, oversight and coordination with the Ohio Turnpike and Infrastructure Commission (OTIC) and JMT
  • Roadway and traffic plans
  • Drainage design and interchange grading
  • Best Management Practice design
  • Culvert design
  • Surveying and right-of-way plans

 

JMT prepared the adjacent roundabout plans at the I-164/SR 626 intersection and created the plans to replace the turnpike bridge with a wider structure. 

 

Complexities of the New Interchange Design


One challenge of the new interchange design was to accommodate a 70-mph horizontal mainline de-sign speed for the terminal of the new northbound I-680 off-ramp if the OTIC toll plaza, south of the new ramp, was removed. The existing horizontal geometry through the plaza did not accommodate this design speed. In addition, the off-ramp terminal also needed to accommodate the existing conditions. The solution was to develop an independent future northbound I-680 alignment, beginning at the end of the OTIC northbound exit ramp, passing through the toll plaza area and tying to the existing north-bound lanes. The northbound lane through the plaza will need reconstruction to match this alignment when the plaza is removed.

 

Another complexity involved the southbound off-ramp. The ramp was a requirement in order to avoid an existing pond, tie into I-680 at a left-turn-ing, fully superelevated curve-to-spiral transition and parallel the SR 164 terminal of the southbound on-ramp. The ramp could not exceed the allowed maximum curve differential and maximum cross-slope grade-break with mainline I-680. This resulted in the first exit curve being to the left,
the same direction as mainline I-680.


A second ramp exit curve to the right was needed to diverge from I-680 and to parallel the southbound on-ramp alignment at the ramps’ intersection with SR 164. The tangent superelevation transition length required between the reverse exit curves resulted in moving the southbound exit terminal to the north, directing the ramp alignment into the adjacent pond. Through continual refinements of the exit ramp geometrics, which changed based on the tie-in location along the mainline spiral alignment, the team found a ramp terminal location that permitted the required design geometry. It avoided the pond and properly directed the exit ramp to parallel the southbound on-ramp at the SR 164 terminal.

 

Roundabout Design


JMT provided design services for a modern round-about, accommodating the additional lanes required for the new interchange. The SR 164 corridor was a rural, two-lane highway with intersections located on each side of the bridge over the turnpike with degraded traffic sight distance and safety. By implementing a roundabout, safety was increased through:

  • Lowered traffic speeds through the corridor via raised splitter islands, chicanes and curbing along the outside travel lanes
  • Adequate sight lines on the approaches and within the circulatory portion of the roundabout
  • Conflict points reduced from 32 (traditional intersection) to eight

 

Each element of the roundabout design had a purpose. The red median islands alerted drivers that they were entering a roundabout, slowing them down, and the landscaping prevented distractions of adjacent movements while also filtering surface waters for treatment.

 

SR 164 Bridge Design


JMT also designed the widening of the existing SR 164 bridge over the Ohio Turnpike, replacing the existing bridge with a wider structure, accommodating additional travel lanes and creating the adequate shoulder-width required by current design standards. This provided:

  • Much needed sight distance for the SR 626 south intersection
  • Adequate clearances for truck maneuvers across the bridge and through the roundabout
  • Vertical clearance improvement for vehicular traffic beneath the bridge on the turnpike

 

Importance to the Traveling Public


As a result of the addition of the interchange, lanes, roundabout and bridge, traffic congestion has decreased. Traffic can exit at the new interchange, taking substantial volume off the local routes and out of the busy Western Reserve Road corridor.

 

Most important, the improvements also increased the traveling public’s safety and provided an innovative route. Since opening in November 2019, the upgrades have also presented the potential to transform the SR 164 corridor into an economic generator.

 

Originally written by Brian Hughes, PE, ms consultants, inc., Steve Gealy, PE, ms consultants, inc., and Joshua Conley, PE, Johnson, Mirmiran & Thompson, ASHE Cuyahoga Valley Section for ASHE Scanner Winter 2021