11. Review Wet 78th St./Laredo Drive Stop Sign Request I It
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:{. CITY OF
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1 \ , CHANHASSEN
I '' 2'4 690 COULTER DRIVE • P.O. BOX 147 • CHANHASSEN, MINNESOTA 55317
(612) 937-1900 by i ~,r:;.=rrItor
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1 MEMORANDUM
TO: Don Ashworth, City Manager __. . ' - r—'°
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FROM Gary Warren , City Engineer �._�•
IDATE: March 8 , 1989
SUBJ: Review West 78th Street/Laredo Drive Stop Sign Request
File No. PW070A-1
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In December, 1988 , staff was directed to complete an analysis to
I determine the possible justification for an all-way stop con-
dition at the West 78th Street/Laredo Drive intersection .
Attached is a report prepared by Howard Preston of BRW which has
II reviewed the "warrant" criteria in accordance with the Minnesota
Manual of Uniform Traffic Control Devices . Mr . Preston ' s report
is quite detailed and reviews everything from traffic volumes and
queuing impacts to the accident history for the intersection.
IAs noted in his report, the intersection at this time does not
meet any of the warrant criteria for implementing an all-way stop
1 condition . The recommendation is that the intersection remain
as-is and that the engineering department annually review the
traffic volumes and accident history at this intersection so that
proper modifications can be made when the warrant criteria are
I met.
As noted in the report, electrical conduit has been installed at
I this intersection in order to easily accommodate the ultimate
traffic condition when traffic lights are eventually warranted.
This would be a $60 ,000 to $80 ,000 investment in today' s dollars .
1 I therefore concur with BRW' s recommendation that the intersec-
tion not be re-signed until such time as the traffic warrant cri-
teria can be met.
1 Attachment
Ii . Memorandum dated March 9 , 1989 from BRW.
cc: Howard Preston, BRW
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PLANNING I
u k' 1 URGAN
ENGINEERING
DESIGN
Li 138W. INC THRESHER SQUARE 700 THIRD STREET SOUTH MINNEAPOLIS.MINNESOTA 55415 PHONE SIT 31(-0700 Fax 617 3701378
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DATE: March 9, 1989 MEMORANDUM
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•;TO: Gary Warren, PE CITY OF SEN
Chanhassen City Engineer 'aft r� l
,1 J'ISOISUVILS.. 1
0 FROM: Howard D. Preston, PE _2
Senior Traffic Engineer / / MAR 0 9 1989
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;; SUBJECT: West 78th Street at Laredo Drive ;'� � II
� � ERI DEPT
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it We have completed the traffic engineering analysis of the intersection of West : II?j 78th Street and Laredo Drive. The analysis consisted of the following steps:
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•! o Collecting traffic volume data and information regarding average vehicle II delay during peak traffic periods, and obtaining intersection accident
records from your Public Safety Department.
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'• o Analyzing the data and then comparing it to the guidelines regarding all-
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ay stop conditions in the Minnesota Manual on Uniform Traffic Control
Devices (MMUTCD) .
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+ o Documenting conclusions and recommendations regarding the quality of traf-
' i fic operations at the intersection.
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it The investigation of the intersection was primarily intended to determine if II
•Hj the installation of an all-way stop condition is needed. It should be noted
H that the MMUTCD states that because stop signs cause a substantial incon- II venience to motorists, they should be used only where warranted. The basic
0 warrants for the all-way stop condition consist of the following:
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li o Traffic Volumes - A minimum total volume entering the intersection of 500
li II vehicles per hour with at least 200 vehicles per hour from the minor
t I street, for at least eight hours of an average day, and with an average
delay to minor street traffic of at least 30 seconds per vehicle during ,
Ii the peak hour.
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it o Traffic Accidents - A minimum of five reported accidents of a type suscep-
` i tible to correction by an all-way stop condition (right and left turn col-
5 lisions and right angle collisions)in a twelve-month period. II
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{ o Combination of Conditions - A combination of high speed, restricted sight
T; distance, and a serious accident record which would indicate the need for
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additional intersection control .
MINNEAPOLIS DENVER PHOENIX TUCSON ST. PETERSBURG
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1 Mr. Gary Warren, PE
March 9, 1989
Page 2
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Traffic volume data was collected at the intersection on January 17, 1989, be-
ll tween the hours of 6AM and 7PM. The data was then analyzed in accordance with
the guidelines in the MMUTCD, and it was determined that the minimum volume
warrant (500 vehicles per hour total and 200 vehicles per hour on the minor
street) was met for only four hours.
1 Vehicle delay data was then collected on January 19, 1989 and average vehicle
delay was calculated in accordance with procedures recommended by the In-
stitute of Transportation Engineers. The data indicates an average delay for
traffic on Laredo Drive of 13 seconds per vehicle (8 seconds for right turning
vehicles and 18 seconds for left turning vehicles) during the peak hour of
conflicting traffic flow on West 78th Street. This average vehicle delay is
1 well below the threshold value of 30 seconds per vehicle suggested in the
MMUTCD. Additional field observations indicate maximum queue lengths of three
vehicles in the right turn lane and six vehicles in the left turn lane during
1 the peak hour.
Traffic accident data was obtained from Chanhassen' s Department of Public
1 Safety and analyzed. The data indicates that there were a total of eight ac-
cidents at the intersection during the period January, 1984 to July, 1988.
This is an average of less than two accidents per year and only two of the ac-
cidents were of a type that would be considered correctable by the installa-
tion of an all-way stop condition. This accident history is obviously below
the five correctable accidents in a twelve month period suggested in the
MMUTCD.
1 The intersection was then observed in the field. This review did not reveal
any sight distance restrictions or other hazardous conditions which might in-
dicate the need for all-way stop control . Based on the results of the
analysis, there appears to be no reason to consider all-way stop control at
this time. The volume of traffic through the intersection does not meet the
minimum threshold volume for the required eight hours per day and the vehicle
1 delay and accident data indicate that the present through/stop intersection
control is functioning satisfactorily.
1 RECOMMENDATIONS
o The traffic engineering analysis indicates that the existing traffic con-
trol at the intersection of West 78th Street and Laredo Drive is function-
ing satisfactorily and the intersection volume, delay, and accident data
do not meet the warrants for the installation of an all-way stop condition
1 as outlined in the MMUTCD. Therefore, it is recommended that the City
retain the existing through/stop intersection control .
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Mr. Gary Warren, PE
March 9, 1989
Page 3
o The accident data does not indicate a serious problem at this time,
however, the number of accidents during the first half of 1988 (the most
recent information currently available) was up considerably from previous
years. This condition combined with the likely increase in future traffic
volumes on West 78th Street due to development/redevelopment in the
downtown area indicates that the intersection should continue to be
monitored an an annual basis and if traffic conditions change, the all-way
stop could be reconsidered.
o If traffic conditions change considerably in the future it may be ap- 1
propriate to consider the installation of traffic signals at the intersec-
tion. Underground conduits, for wiring the traffic signal were installed
as part of the downtown reconstruction. However, traffic signals would be
a very expensive solution (approximately $60,000 to $80,000) and would
probably be considered appropriate only if a serious traffic problem could
be documented at the intersection.
o Several additional points regarding all-way stop control should be noted.
1) All-way stop control significantly increases total intersection delay
at locations where the volume on the entering legs is not ap-
proximately equal .
2) A significant body of research regarding all-way stop control indi- 1
cates that step signs have never been particularly effective in
reducing vehicle speeds.
3) The MMUTCD prohibits the use of stop signs solely for the purpose of
speed control .
4) The City could be held liable for accidents that occur at an unwar- 1
ranted stop sign.
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CITY OF CHANHASSEN
WEST 78TH STREET/LAREDO DRIVE
Table 1
Traffic Count A11-Wav Stop Warrant Summary
Meets Warrant
Time of Laredo Drive West 78th Street 500 Veh/Hr 200 Veh-Ped/Hr both
Day (N. Approach) (E. Approach) (W. Approach) (Total) (Minor Street)
6:00 AM - 7:00 AM 82 109 319
7:00 AM - 8:00 AM 163 235 439 x
8:00 AM - 9:00 AM 236 238 290 x x x
9:00 AM - 10:00 AM 157 214 180 x
10:00 AM - 11:00 AM 146 178 183 x
11:00 AM - NOON 168 245 231 x
NOON - 1:00 PM 202 301 250 x x x
1:00 PM - 2:00 PM 170 249 167 x
2:00 PM - 3:00 PM 144 254 169 x
3:00 PM - 4:00 PM 220 382 208 x x x
4:00 PM - 5000 PM 206 458 304 x x x
5:00 PM - 6:00 PM 123 531 231 x
6000 PM - 7:00 PM 122 373 284 x
Total Hours Exceeding Requirements 13 4 4
Number of Hours Necessary to Meet Warrant 8
Warrant Met/Not Met Rat Net
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CITY OF CHANHASSEN
WEST 78TH STREET/LAREDO DRIVE
Table 2
Intersection Accident Suaaary
Type of Accident Severity
Total
Year Right Side Head Rear Illegal Left Turn Right Rao Off Object Property Personal 4 of
Angle Swipe On End Turn lOppa=_ing)(Crassing) Turn Road Ped. In Read Other Gaazge Injury Eatal Accidents
1984 1 1 1
1985 U
1986 1 1 2 2
1987 0
1988 2 1 2 4 1 5
TOTAL 2 0 0 2 0 0 0 0 0 0 0 4 6 2 0 8
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ME NM MO - NM - MI OM I - ME - ME - - NE Ns am liso