Loading...
HomeMy WebLinkAboutRENNAT SUBDIVISION - FDP200006 - DOCUMENT MARKUPS - ROUND 1 - VARIANCE REQUESTFORT COLLINS: 301 North Howes Street, Suite 100, 80521 | 970.221.4158 GREELEY: 820 8th Street, 80631 | 970.395.9880 | WEB: www.northernengineering.com October 18, 2019 City of Fort Collins P.O. Box 580 Fort Collins, CO 80522 RE: Variance Request for the Minimum Centerline Radius Table 7-3 – Larimer County Urban Area Street Standards Project # 1204-003 Variance description: This is a request for a variance from the standard contained in Table 7-3 of the Larimer County Urban Area Street Standards (LCUASS) which pertains to the minimum centerline radius of streets. The criteria states that minor collector streets should have a minimum 600-ft radius. The Rennat Subdivision proposes to reduce the minimum centerline radius of Zephyr Road, between Burly Tree Drive and Rosen Drive, to 350-ft based on LUCASS and on the AASHTO Geometric Design of Highways and Streets (AASHTO-GD) criteria. The purpose for the 350’ centerline radius is to connect the proposed Zephyr Road to Red Willow Drive. Red Willow Drive is an existing north-south road that provides access to Linden Park Subdivision. Justification: The minimum road centerline radius is based on the stopping sight distance for vehicles as well as the threshold of driver comfort and to provide a margin of safety against vehicle skidding. It is our professional opinion that the proposed roadway geometry will meet the intent of this requirement. The 600-ft radius for a minor collector required by LCUASS is based on a 40-mph design speed with a 30-mph posted speed. The Rennat Subdivision is proposing to reduce the posted speed along Zephyr to a 25-mph posted speed and use a 30-mph design speed. Per LCUASS Table 7-6 a 200-ft stopping sight distance is required for a design speed of 30-mph. The attached exhibit shows the stopping sight distance overlaid on the proposed road alignment. Reducing the centerline radius does not add any obstructions to the driver or affect the stopping sight distance of the vehicle. At 30-mph the proposed centerline radius also has little effect on vehicle control. Per AASHTO “Green book” Table 3-7 (Minimum radius using limiting values of e and f) the minimum radius using a design speed of 30-mph is 250-ft. Conclusion The variance requested in this letter will not have an adverse impact on the Cities capital and maintenance costs, nor will it reduce the design life of the respective improvements. The requested waiver will not be detrimental to the public health, safety, or welfare. We believe this variance is a minimum change that will afford relief and is the least modification possible. If you should have any questions as you review this Variance Request, please feel free to contact us. Sincerely, NORTHERN ENGINEERING SERVICES, INC. Mason Ruebel Project Engineer ZEPHYR RD MISTY MEADOW DR 200' STOPPING SIGHT DISTANCE 12' TRAVEL LANE 12' TRAVEL LANE 5' BIKE LANE 8' PARKING SIGHT LINE R350' MINIMUM CENTERLINE RADIUS EXHIBIT STOPPING SIGHT DISTANCE FORT COLLINS, CO E NGINEER ING N O R T H E RN 10.18.19 P:\1204-003\ADMIN\VARIANCE\CENTERLINE RADIUS EXHIBIT.DWG ( IN FEET ) RENNAT SUBDIVISION 1 inch = ft. 50 0 50 Feet 50