Vine Drive and Shields Street Intersection Improvements
The goals for this project are to: improve safety for vehicles, bicycles and pedestrians, correct the sub-standard horizontal geometry of the intersection, and improve air quality through reduced vehicle wait time.
In 2011, the City received a federal grant administered through the Colorado Department of Transportation (CDOT) to design and construct intersection improvements at Vine Drive and Shields Street.City Engineering recently completed an Arterial Intersection Priority Study which ranked the Vine and Shields intersection in the top ten for needed enhancements. Major reasons this intersection is at the top include: poor horizontal geometry, deficient and /or non-existent bicycle and pedestrian facilities, higher than average vehicle accident rates and elevated levels of vehicle delay (congestion). The improvements will follow a multi-modal approach to create a safer intersection for all users.
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Conceptual layout for enhanced signalized intersection.
Conceptual layout for single-lane roundabout
The project began with an alternatives analysis, per City of Fort Collins Ordinance 2001-120, which mandates the evaluation of a signalized option and a roundabout option at arterial intersections. The City completed this analysis in the spring of 2012 and took the staff recommendation to City Council in the summer of 2012. The analysis compares the two alternatives in terms of: safety, right-of-way requirements, cost, constructability, multi-modal enhancements, and operations.
The signalized intersection would add an eastbound right-turn lane, a northbound left-turn lane and southbound left- and right-turn lanes. Long, sweeping horizontal curves would be added on both approaches for Vine Drive to straighten the travel lanes through the intersection.
The single-lane roundabout would be built around an oval central island, rotated to the northwest and southeast directions to correct the Vine Drive alignment deficiency. The entrances and exits to and from the roundabout would be single lanes in all directions.
Both improvement types show an equal crash reduction (vehicle to vehicle crashes) of 33% as compared to the existing conditions. In general, roundabouts tend to have less severe accidents as opposed to signalized intersections. This can be attributed to lower approach speeds for the roundabout where drivers tend to sideswipe or rear-end one another in a crash situation. The signalized intersection has a higher probability of head on collisions and T-bone crashes where drivers are making left turns in front of oncoming traffic.
Right-of-way & Project Footprint
The signalized intersection will require approximately 8,000 square feet of right-of-way while the roundabout will require 8,130 square feet of right-of-way. The improvements for both options will be carried 650 feet north of Vine Drive to the Arthur Ditch. The signalized intersection footprint will extend 400 feet east, west and south of the intersection; whereas the roundabout footprint will extend 250 feet east, west and south of the intersection. Therefore, the overall footprint of the roundabout is approximately 20% less than the overall signalized intersection footprint. Temporary construction easements will be necessary for both options, but were not included at the conceptual level.
The signalized intersection design and construction cost estimate is $1.64M. The roundabout design and construction cost estimate is $1.43M. The roundabout has a 12% lower estimated cost than the signalized intersection because of the smaller footprint needed to transition back into existing lane configurations.
This is a measure of the level of impacts to the travelling public during construction. Both options would be buildable under existing traffic and both may require temporary signals. The signalized intersection improvements would mostly occur outside of the existing lanes. The roundabout intersection would be built one half at a time.
Currently, there are no pedestrian facilities on the northwest and northeast corners. Bike lanes do not existing on the north and east legs of the intersection. Both improvements options will address the deficient and / or non-existent bicycle and pedestrian facilities by providing accessible crosswalks, corner ramps and on-street bike lanes. The roundabout option gives cyclists the option of riding on-street through the circulating roadway or by taking crosswalks as a means of passing through the intersection. A “conflict point” is a location where the paths of two motor vehicles, bicycles or pedestrians connect. The signalized intersection has 32 vehicle to vehicle conflicts and 24 vehicle to pedestrian conflicts. The single-lane roundabout has 8 vehicle to vehicle conflicts and 8 vehicle to pedestrian conflicts. Numerous studies completed around the United States have shown that reduced conflict points at an intersection result in a proportional reduction in injury accidents.
The peak hours (7-8 AM and 5-6 PM) were analyzed using a traffic software package to simulate each alternative. The results of the analysis were compared to existing conditions under the categories of vehicle delay, total number of stops, vehicle fuel consumption and vehicle emissions. The signalized intersection showed the following percent reductions: vehicle delay 40%, total stops 20%, fuel consumption 20% and emissions 19% as an average of the 2 peak hours. The roundabout intersection showed the following percent reductions: vehicle delay 75%, total stops 70%, fuel consumption 37% and emissions 39% as an average of the 2 peak hours. Both alternatives reduce delay and emissions when compared to the existing conditions; however, the roundabout option exhibits a significantly greater decrease across the four major categories of the peak hour modeled conditions. Additionally, the roundabout will out perform the signalized intersection in the off peak hours when traffic volumes are lower and the user will not have to wait for a traffic signal to cycle through it’s programmed green times.
The City’s engineering staff is recommending a single-lane roundabout as the preferred option. Final approval regarding the type of intersection design will come from City Council in the summer of 2012. The City will design and construct a concrete intersection at Vine Drive and Shields Street and incorporate the following items into the project: accessible crosswalks for all legs of the intersection, bicycle lanes and sidewalks (connections for both modes of transportation to the Poudre River Trail, north of the intersection, in conjunction with Larimer County’s Shields Street improvements), storm sewer and other utility improvements, and landscape enhancements plus urban design elements.
- Federal grant administered through CDOT (majority of the funding at 60%)
- Building on Basics (BOB) Intersection Funds (20%)
- Regional Road Fee (shared with Larimer County) (20%)
- Spring 2012: presented alternatives analysis to the Transportation Board and public outreach with businesses, residents and Poudre School District
- Summer 2012: open house, project went to City Council for approval and appropriation of funds
- Fall 2012: Request for Proposal (RFP) for design
- 2013: Preliminary Design
- 2014: Final Design
- 2015: Construction
The City of Fort Collins and Larimer County held a combined open house on June 16, 2011 to announce the project kick-off for the City’s Vine and Shields intersection improvements and the County’s North Shields Street improvements. Additional open houses will be held throughout design and construction to keep the community informed.
Tim Kemp, Civil Engineer II