The document analyzes using a roundabout to solve traffic issues at the intersection of State Routes 315 and 750. While roundabouts generally provide safety and traffic benefits, this site poses challenges due to a lack of space, grade issues, and proximity to the Olentangy River. Construction would require extensive land acquisition and hillside removal, negatively impacting the environment and private property. Mitigation of impacts is unlikely given the exceptional quality of the river habitat. Alternative solutions are recommended that limit growth needs and involve stakeholders early in the planning process.

1. State Routes 315 and 750:
A Roundabout Approach to a Solution
Ian Ausprey. Ariel Godwin. Amanda King.
Stephen Mayer. Anna McCreery.

3. 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

4. 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.

5. 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

11. Site Analysis: Private Property Take
• Alternatives 1-2: 11,500 sq. feet
• Alternatives 3-4: 57,820 sq. feet

12. 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

13. 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.

14. 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.

15. Stakeholder Analysis: Scenic Rivers
• Concerned construction’s potential impact on:
• Wildlife
• River health
• Aesthetics
• Preference would be absolutely no impacts on
the Olentangy River

16. 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

17. 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

18. 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

19. 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

20. Stakeholder Analysis: ODOT
• Considering 5 alternatives, none of which is a
roundabout
• Contact person for project was unwilling to
comment specifically regarding a roundabout

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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