Ian Ausprey. Ariel Godwin. Amanda King. Stephen Mayer. Anna McCreery.

State Routes 315 and 750: A Roundabout Approach to a Solution

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

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.

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

Site Analysis: Private Property Take

• Alternatives 1-2: 11,500 sq. feet

• Alternatives 3-4: 57,820 sq. feet

0

200000

400000

600000

800000

1000000

1200000

1400000

1600000

1800000

2000000

Alternative 1-2 Alternative 3-4

Cubic Feet

Roundabout Footprint Approaches & Line of Sight

Site Analysis: Hillside Removal

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.

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.

Stakeholder Analysis: Scenic

Rivers• Concerned construction’s potential impact

on:• Wildlife• River health• Aesthetics

• Preference would be absolutely no impacts on the Olentangy River

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

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

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

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

Stakeholder Analysis: ODOT

• Considering 5 alternatives, none of which is a roundabout

• Contact person for project was unwilling to comment specifically regarding a roundabout

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

• 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

Environmental Consequences

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

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

• 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

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

Conclusions