HomeMy WebLinkAbout04-13 Cottonwood MAIM
Ann* Montana Department of Transportation
PO Box 201001
Helena, MT 59620-1001
Memorandum
r Ilk I WrM DISTRICT To: Kraig McLeod, P. IAIQR
Safety Engineer
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From:" Danielle C. Bolan, P.E.
Traffic Operations Engineer
Date: March 22, 2013
Subject: Cottonwood Rd& Stucky Rd—Bozeman
Traffic Control Analysis - -- �—'
The intersection of Cottonwood Rd& Stucky Rd was identified in the 2011/2012 HSIP List, and
at the request of the Traffic Safety section, alternate traffic control options were studied.
Analysis shows that a roundabout will accommodate future traffic volumes,and will address the
failure-to-yield and right-angle crash trend. Until a roundabout can be funded and installed, an
all-way stop with flashers is recommended as an interim solution.
Existing Site Conditions
The study site is a four-legged intersection located in Gallatin County,just outside Bozeman's
southwestern urban boundary. The surrounding lane use is agricultural and rural residential.
Bozeman School District owns the property in the southeast quadrant and plans to build a high
school in the future.
Cottonwood Rd (S-345) is a major collector running north and south. The posted speed limit is
55mph, and traffic flows freely with no stop control. Stucky Rd is an off-system minor collector
running east and west. The posted speed limit is 40mph,and traffic is stop-controlled. Both
roads have two lanes and no shoulders. Large trees and bushes in the northeast and southwest
quadrants limit sight-distance for vehicles on Stucky Rd. The site is shown in Figure 1.
Traffic Volumes
Turning movement counts were collected by MDT on February 27,2013 from 7:00-9:00am,
11:OOam-1:OOpm, and 4:00-6:00pm. The morning peak hour occurred from 7:30-8:30am, the
noon peak from 12:00-1:OOpm and the evening peak from 5:00-6:OOpm.
Page 2 of 6
Noteworthy conditions include: a very high southbound left-turning volume in the morning,a
high eastbound volume exiting the intersection in the morning, and higher side-street volumes
than mainline volumes in the evening. Peak hour volumes are shown in Figures 2 and 3.
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Figure 1 —Cottonwood Rd & Stucky Rd — Bozeman
Cottonwood Rd & Stucky Rd Cottonwood Rd & Stucky Rd Cottonwood Rd & Stucky Rd
AM Peak 7:30-8:30am Noon Peak 12:00-1:00pm PM Peak 5:00-6:00pm
0 305 0 106 0F 165
3 3 3
c c
O O W N O T Q C m tD
� v v
Stucky ice. c} Stucky 1 } {> �$tucky
64 54 118
11 40 3 Q 28 9 120 N
°D 1021--f' 8 ,n 44 C� 0 92 J 35
5 6 6
Stucky '�� Stucky Stucky \ �'
1 Irr p u v � •°
Q V I W O Q Q N O N M
234 T 66 v N) T 92 u { �
Figure 2 — Existing Traffic Volumes: Cottonwood Rd & Stucky Rd (February 2013)
Page 3 of 6
-- -- AM Peak Hour- - -- Noon Peak Hour - —1 PM Peak Hour - �}
Entering & Exiting Volumes f Entering & Exiting Volumes I Entering & Exiting Volumes
v I
o o � , o 0 o
V� - V oil
V _ Stucky U Stucky Jr Stucky
48 !' 112 ;� Ot 89 135 273
118 403 53 j 108 107 j
' /� �/
Stucky �� Stucky i., r Stucky
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o °o °
°f c c c
o N N o N
V U U
Figure 3—Entering& Exiting Volumes: Cottonwood Rd &Stucky Rd (February 2013)
Crash History
This intersection was originally identified as a high crash location in 2001. In 2002, vegetation
was requested to be trimmed back through the District. The crash trend did not reemerge until
2008-2010. A field review conducted in May 2012 by Safety and District Staff recommended
that vegetation within MDT right-of-way again be removed, and that alternate stop control be
evaluated by Engineering Analysis.
During the five year period from January 1, 2008 through December 31, 2012, a total of 13
intersection-related crashes were reported. Of these 13 crashes: 8 were right-angle crashes, 2
were side-swipes, 2 were roll-overs, and 1 hit a fixed object. Five crashes resulted in injuries, and
8 were property damage only. All crashes occurred during clear or cloudy weather. Eleven were
during daylight hours, and 2 were after dark. Seven were on dry roads, 5 on snow/ice,and 1 on
wet roads.
The 8 right-angle crashes and 1 roll-over were due to traffic on Stucky Rd failing to yield the
right-of-way to traffic on Cottonwood Rd. Five vehicles stopped at the stop sign but pulled out
while unsafe, 3 vehicles ran the stop sign, and 1 is unclear whether the vehicle stopped or not.
The 5 crashes involving vehicles that obeyed the stop sign are considered addressable though
installation of an all-way stop or a roundabout. The crashes involving vehicles running the stop
sign are addressable through installation of a roundabout.
Most eastbound crashes involved northbound vehicles,and all westbound crashes involved
southbound vehicles. The limited sight triangle is likely contributing to these crashes,because
these are the sight-lines blocked by vegetation. Installation of a roundabout or an all-way stop
would address intersection sight-distance problems.
Page 4 of 6
Capacity Analysis and Operations
Capacity analysis of the intersection was performed using HCS2010 and Sidra software. The
morning and evening peak volumes were used to calculate the Level of Service(LOS) and delay
at the intersection under various conditions: two-way stop, four-way stop, and a roundabout.
Future 20-year conditions were also analyzed using a 1.5% growth rate for both roads.
Under existing(2-way stop)conditions, traffic on Stucky Rd is experiencing LOS F and E during
the morning peak, with delays up to 90 seconds. During the evening peak, all approaches are
operating at a LOS C or better. Existing LOS results for 2-way stop control are shown in Table 1.
Under all-way stop control, current traffic volumes would experience LOS C or better during the
morning peak and LOS B or better during the evening peak. However, high left-turning volumes
cause the southbound approach to fail under 20-year projected volumes. LOS results for all-way
stop control are shown in Tables 2 and 3.
A roundabout would allow current traffic volumes to operate at a LOS C or better during the
morning peak, and a LOS B or better during the evening peak. (The highest delay of 20sec in the
morning is just on the threshold for LOS B/C.) The 20-year projected volumes show all
movements could continue operating at a LOS C or better. Capacity results for a roundabout are
shown in Tables 4 and 5.
The southbound approach currently meets MDT's criteria for installation of a dedicated left-turn
lane. This is evident in the 20-year all-way stop analysis, which shows the southbound approach
failing under existing lane configurations. The need for a left-turn lane would be eliminated with
the installation of a roundabout.
Table 1
2013 Existing LOS: 2-Way Stop
Cottonwood Cottonwood Stucky Stucky
NB SB EB WB
AM Peak Hour Lt-Th-Rt Lt-Th-Rt U-Th-Rt U-Th-Rt
Volume/Capacity 0.01 0.27 0.86 0.60
Delay(sec) 7.4 8.7 90.7 36.5
Level-of-Service A A F E
PM Peak Hour U-Th-Rt U-Th-Rt Lt-Th-Rt U-Th-Rt
Volume/Capacity 0.01 0.04 0.21 0.54
Delay(sec) 7.4 7.5 13.6 15.4
Level-of-Service A A B C
Page 5 of 6
Table t & 3
2013 LOS: All-Way Stop
Cottonwood Cottonwood Stucky Stucky
NB SB EB WB
AM Peak Hour Lt-Th-Rt Lt-Th-Rt Lt-Th-Rt U-Th-Rt
Delay(sec) 11.1 18.1 11.0 10.8
Level-of-Service B C B B
PM Peak Hour Lt-Th-Rt Lt-Th-Rt Lt-Th-Rt Lt-Th-Rt
Delay(sec) 9.1 9.7 9.0 11.6
Level-of-Service A A A B
2033 Future LOS: All-Way Stop
Cottonwood Cottonwood Stucky Stucky
NB SB EB WB
AM Peak Hour Lt-Th-Rt Lt-Th-Rt Lt-Th-Rt Lt-Th-Rt
Delay(sec) 18.0 73.6 15.5 15.4
Level-of-Service C F C C
PM Peak Hour Lt-Th-Rt Lt-Th-Rt Lt-Th-Rt Lt-Th-Rt
Delay(sec) 10.7 11.6 10.4 19.5
Level-of-Service B B B C
Tables 4 & S
2013 LOS: Roundabout
Cottonwood Cottonwood Stucky Stucky
NB SB EB WB
AM Peak Hour Lt Th Rt Lt Th Rt Lt Th Rt Lt Th Rt
Volume/Capacity 0.34 0.34 0.34 0.36 0.36 0.36 0.20 0.20 0.20 0.16 0.16 0.16
Delay(sec) 20.0 13.8 13.7 15.6 9.4 9.3 18.8 8.2 11.4 15.8 5.2 8.4
Level-of-Service C B B B A A B A B B A A
PM Peak Hour Lt Th Rt Lt Th Rt Lt Th Rt Lt Th Rt
Volume/Capacity 0.11 0.11 0.11 0.14 0.14 0.14 0.11 0.11 0.11 0.33 0.33 0.33
Delay(sec) 16.2 10.0 9.9 16.6 10.4 10.3 16.0 5.4 8.6 15.5 4.9 8.1
Level-of-Service B A A B B B B A A B A A
2033 Future LOS: Roundabout
Cottonwood Cottonwood Stucky Stucky
NB SB EB WB
AM Peak Hour Lt Th Rt Lt Th Rt Lt Th Rt Lt Th Rt
Volume/Capacity 0.48 0.48 0.48 0.45 0.45 0.45 0.28 0.28 0.28 0.20 0.20 0.20
Delay(sec) 23.3 17.0 16.9 15.9 9.7 9.6 20.1 9.5 12.7 16.1 5.5 8.7
Level-of-Service C B B B A A C A B B A A
PM Peak Hour Lt Th Rt Lt Th Rt Lt Th Rt Lt Th Rt
Volume/Capacity 0.13 0.13 0.13 0.18 0.18 0.18 0.15 0.15 0.15 0.42 0.42 0.42
Delay(sec) 16.6 10.3 10.2 17.1 10.8 10.7 16.4 5.8 9.0 15.8 5.2 8.4
Level-of-Service B B B B B B B A A B A A
Page 6 of 6
Conclusions
Analysis shows that during the morning peak, traffic on Stucky Rd is currently experiencing
poor to failing levels-of-service. In the evening, higher side street volumes are seen on Stucky
Rd than on mainline Cottonwood Rd.
Nine of 13 crashes were caused by traffic on Stucky Rd failing to.yield the right-of-way to traffic
on Cottonwood Rd. Three vehicles did not obey the stop sign. Five vehicles obeyed the stop
sign, but still pulled in front of oncoming traffic, indicating a sight-distance problem.
All-way stop control would operate reasonably under existing conditions, but a high left-turning
volume would cause the southbound approach to fail under 20-year projected volumes. Current
volumes meet the criteria for a dedicated left-turn lane, which would introduce more conflict
points to the intersection. An all-way stop could address sight-distance problems, and the 5
crashes involving vehicles that obeyed the stop sign; it would not address the 3 crashes involving
vehicles running the stop sign.
A single-lane roundabout is projected to accommodate all future volumes, while still maintaining
acceptable levels of service. A roundabout would reduce the number of conflict points, mitigate
sight-distance issues, and address all 9 of the failure-to-yield crashes.
Recommendation
A single lane roundabout is recommended at this intersection. Until a roundabout can be funded
and installed,all-way stop with overhead flashers is an appropriate interim measure. New stop-
bars should be painted on all legs.
If you have any questions,please call Tasha King at 444-9452.
DCB:TLK:MEMO COTTONWOOD STUCKY.docx
Copies: Roy Peterson, P.E. —Traffic& Safety
Jeff Ebert—Butte District
Ivan Ulberg, P.E.—Traffic& Safety
Dustin Rouse,P.E.—Butte District
Lee Alt—Butte District
Patricia Burke, P.E. —Traffic& Safety
Tasha King, P.E.—Traffic& Safety
Traffic& Safety File