HomeMy WebLinkAbout039 Curve Radius Design Standard Modificiation Request_updated•
• Engineers and Land Surveyors
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1
February 9, 2023
Mikaela Schultz
City of Bozeman Transportation and Engineering
20 E. Olive
Bozeman, MT 59771
RE: Canyon Gate Curve Radius Design Standard Modification -Update
Mikaela:
We discussed the proposed roadway curvature with Taylor Lonsdale and he recommended and
tentatively supported a modification to the Design Standards to allow a 100’ centerline curve radius.
Please find the following updated documentation in support of said modification. This update is
based on receiving more accurate Bozeman Ladder Truck Dimensions from the City.
A 100’ curve radius was proposed in lieu of a 150’ radius to encourage lower speeds and provide
traffic calming. The 100’ radius also fits more appropriately within an urban street framework since it
reduces the length of the curve and allows buildings to better front the street. The proposed 100’
radius is an appropriate balance between traffic conveyance, speed reduction, and emergency
vehicle access.
To verify that this curve will not jeopardize emergency access, turning movements were analyzed
with Autodesk Vehicle Tracking. The updated modeling criteria and swept path results are shown in
the revised Figure 1, attached. The design vehicle is the largest Bozeman Ladder Truck as provided
by the fire department on 2-9-23. The model was conducted for the inside travel lane, but results
would be the same for all 100’ radius curves and travel directions. The maximum width of the swept
path (including vehicle overhangs) is 15.61’ when traveling around a curve with a 100’ centerline
radius. The proposed street section is 35’ wide, with (2) 10’ travel lanes and (2) 7’ parallel parking
lanes. The turning analysis shows that the proposed street section, with a 100’ radius curve,
comfortably accommodates the largest fire truck (and mirror clearance) within the 20’ driving surface.
Please let us know if you have any additional questions.
Sincerely,
Stahly Engineering & Associates
Cordell D. Pool, PE
Associate Principal
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FIGURE 1
PROFESSIONAL ENGINEERS & SURVEYORS
TURNING MOVEMENTANALYSIS
CANYON GATE
STAHLY ENGINEERING & ASSOCIATES
CANYON GATE INVESTORS, LLCBOZEMAN, MONTANA
00 30'60'