HomeMy WebLinkAboutRENNAT SUBDIVISION - PDP190011 - SUBMITTAL DOCUMENTS - ROUND 2 - 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