HomeMy WebLinkAboutRENNAT SUBDIVISION - FDP200006 - SUBMITTAL DOCUMENTS - 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
February 12, 2020
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 intersection and 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. The vertical profile of Zephyr will still use a 40-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. An Exhibit showing the intersection sight distance has also been
included comparing the sight distance at 30 & 40 mph. The proposed geometry is sufficient for
30-mph speeds at the intersection of Misty Meadow Drive and Zephyr Road. A sight distance
easement will be provided for vehicles at the intersection of Rosen Drive and Red Willow Drive
to ensure adequate sight distance looking north on Zephyr Road. 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
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LID
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ZEPHYR RD
MISTY
MEADOW DR
SIGHT LINE (30MPH)
R350'
310' SIGHT DISTANCE (30MPH)
SIGHT LINE (30MPH)
ROSEN DR
SIGHT LINE (40MPH)
660' SIGHT DISTANCE (40MPH)
RED WILLOW DR
660' SIGHT DISTANCE (40MPH)
SIGHT LINE (40MPH)
310' SIGHT DISTANCE (30MPH)
INTERSECTION SIGHT DISTANCE EXHIBIT
ZEPHYR ROAD & MISTY MEADOW DRIVE
FORT COLLINS, CO
E NGINEER ING
N O R T H E RN
10.18.19
P:\1204-003\ADMIN\VARIANCE\SIGHT DISTANCE EXHIBIT_1.DWG
RENNAT SUBDIVISION
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ZEPHYR RD
MISTY MEADOW DR
SIGHT LINE (30MPH)
R350'
ROSEN DR
SIGHT LINE (40MPH)
RED WILLOW
DR
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INTERSECTION SIGHT DISTANCE EXHIBIT
ZEPHYR ROAD & ROSEN DRIVE
FORT COLLINS, CO
E NGINEER ING
N O R T H E RN
10.18.19
P:\1204-003\ADMIN\VARIANCE\SIGHT DISTANCE EXHIBIT_2.DWG
( IN FEET ) RENNAT SUBDIVISION
1 inch = ft.
100 0 100 Feet
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