Roundabout feasibility analysis


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This presentation shows the results of a class project analyzing transportation alternatives to ease congestion at a Ohio major intersection. My group was assigned the roundabout alternative, and our analysis included site analysis using GIS, stakeholder concerns, environmental issues, feasibility of a roundabout, and final recommendations.

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Roundabout feasibility analysis

  1. 1. State Routes 315 and 750:A Roundabout Approach to a Solution Ian Ausprey. Ariel Godwin. Amanda King. Stephen Mayer. Anna McCreery.
  2. 2. Advantages to Roundabouts •Improved Vehicle Safety • Both fewer crashes, and fewer injury crashes •Reduced wait time • Roundabouts have less traffic delay that comparable light-controlled intersections •Environmental impact • Reduced air pollution, oil and car debris runoff
  3. 3. Disadvantages to Roundabouts • Bicycle & Pedestrian Safety Problems • Increased accidents involving bicycles & pedestrians • Capital Cost • New roundabouts cost around $500,000 for construction • Additional costs for land acquisition, road curves to slow entering traffic, illumination, and signage.
  4. 4. Site Analysis: Minimum Site Requirements for Constructing a Roundabout • Central island > 100 ft diameter • < 4% grade across intersection • < 4% grade for all approaches • Clear line of site 50 ft. from approach intersections • Approach flaring 130 ft. from intersection
  5. 5. Site Analysis: Private Property Take • Alternatives 1-2: 11,500 sq. feet • Alternatives 3-4: 57,820 sq. feet
  6. 6. Site Analysis: Hillside Removal 2000000 Roundabout Footprint Approaches & Line of Sight 1800000 1600000 1400000 1200000 1000000 Cubic Feet 800000 600000 400000 200000 0 Alternative 1-2 Alternative 3-4
  7. 7. Stakeholder Analysis: City of Powell• Supportive of any solutions ODOT is willing to provide since the road is slipping into river• Will not be pleased if congestion is lessened because of its impact on downtown Powell.
  8. 8. Stakeholder Analysis: Delaware County• Prefer a method that best facilitates traffic from Columbus to Delaware County and enables future growth in the area.• Economic activity is important to the area.
  9. 9. Stakeholder Analysis: Scenic Rivers• Concerned construction’s potential impact on: • Wildlife • River health • Aesthetics• Preference would be absolutely no impacts on the Olentangy River
  10. 10. Stakeholder Analysis:Friends of the Lower Olentangy River Watershed • Distressed that construction would harm the “good part” of the river • The Olentangy is “Exceptional Warm Water Habitat” at the intersection • Preferred Alternatives 3-4 if necessary
  11. 11. Stakeholder Analysis: Homeowners’ Association • According to the homeowners’ association, property owners in the area are concerned about: • Property rights • Traffic issues • The green aesthetic of the area • Regrading for the roundabout would cut into residential lots and require driveways to be rebuilt
  12. 12. Environmental Consequences • Homeowners are concerned about the greenery and the extent to which roundabout construction would “scar the land” • Homeowners are divided: • Some would like to see congestion eased • Some like the congestion because it keeps traffic slow • All value the forested character of the area and would not support a solution that would change that character
  13. 13. Stakeholder Analysis:Regional Planning: MORPC• 200 roadway projects under review in the region• MORPC Engineers considered a roundabout too expensive• Excessive development has been a problem in the area• Conflict between ODOT and Powell over development too close to the river
  14. 14. Stakeholder Analysis: ODOT• Considering 5 alternatives, none of which is a roundabout• Contact person for project was unwilling to comment specifically regarding a roundabout
  15. 15. Environmental Consequences• Removal of riparian vegetation • Removal of organic material • Increased erosion potential around river • Implications for species survival/dominance• Disruption of mussel beds and other species• Ground water flow impacts• River water quality • Siltation of river • Acidification of river water during construction• Increased imperviousness • Stormwater runoff implications
  16. 16. Environmental Consequences• Very high quality section of the Olentangy River at this site• Meets Exceptional Warm Water Habitat (EWWH) criteria • “Unusual and exceptional” assemblages of organisms • High diversity of species, including endangered mussels• Pristine water quality
  17. 17. Consequence Mitigation Techniques• Potential environmental benefit of increased shade from bridge to offset less tree cover• Relocation of mussels and other valuable species• Designate additional riparian conservation sites within watershed• Use center of roundabout as rain garden to mitigate increase in impervious surface• Exceptional quality of river and surrounding habitat at this site makes the potential for comparable mitigation unlikely
  18. 18. Conclusions • Roundabouts generally meet many 315/750 intersection needs • Traffic management, increased safety, improved air quality • However, intersection lacks physical suitability for roundabout needs • Lack of space • Grade • Proximity of river • Prohibitive economic and environmental costs
  19. 19. Conclusions • Lessons learned for transportation planning • Problems with building close to river and other environmentally valuable sites • Importance of multi-modal transportation options • Connection between land use, growth, and transportation
  20. 20. Conclusions • Future Recommendations • Limit need for this and other vulnerable roads • Factor in projected commercial and residential growth/decline in transportation planning projects • Factor in energy, time, and other commuting costs for greater Delaware County area • Assemble stakeholders early in project planning process to achieve community buy-in