* Agenda�b b t-
WORK SESSION AGENDA
June 26, 1995 7:00 p.m. t�
0
1. Business From Mayor and Council
2. Business from Manager
3. Resolution -Stillwater River/Shady Lane -Master Plan Amendment
4. Resolution -third Annexation
5. Resolution -Boller Annexation
6. Resolution-Myren Annexation
7. Resolution -Fairway Blvd. Phases VI, VII and VIII o
�i8. Flathead Industries -Conditional Use Permit f"-7
9. Request for Proposals V
Participation in the Commercial Rehabilitation Loan Program
July 5, 1995
10. Discuss Northwest Montana Mental Health pending law suit
11. Labor Contracts-Police/Fire/Salary Ordinance
(�" Discussion concerning Sewer Rate Analysis-Morrison/Maierle
J3Budget Presentation/Budget Calendar
Appointments ►ok oaA
f
Airport Advisory Board C
Board of Adjustments &:w
Letters of Interest accepted until
July 7, 1995 5:00 p.m.
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Continued
Extension of Services Plan
Construction Standards
Next Regular Council Meeting July 10, 1995 7:00 p.m.
Next Work Session July 17, 1995 7:00 p.m.
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1127 Alderson Ave.
Suite 204
Billings, MT 59102
(406) 248-5083
Kalispell, MT 59903 June 16, 1995
Re: 1992 Safety Improvement Study
Fifth Street & Third Avenue West
Dear Bob:
I am writing this letter to explain the reasons for parking restriction length variations at the above
noted intersection, as per your request. I have also attached support documents and information for
your use.
The first attachment is page 761 from the AASHTO Green Book, "A Policy On Geometric Design
of Highways and Streets", 1990. This page contains Figure IX-39, which covers minimum sight
distances for intersections, Case IIIA, which is specifically for the crossing maneuver from a stop
sign. This is the minimum intersection sight distance case. Cases IIB and C cover right and left turns,
which both require more sight distance. From Figure IX-39, minimum sight distance for a two lane
road at 25 mph would be approximately 250 feet. According to AASHTO, this distance is measured
from a point 20 feet behind the edge of pavement or curbline.
Since the use of AASHTO standards within established residential neighborhoods and on local streets
can sometimes be very restrictive, we have calculated sight distance on a site by site basis, depending
on geometry, speeds and other individual conditions. In the case of 5th and 3rd, we found that a
design speed of 25 mph was sufficient, rather than 30 mph (speed limit plus 5 mph). AASHTO
distances are also based on a mixture passenger cars, single unit vehicles and trucks in the traffic
stream. Acceleration characteristics for trucks are very different than for cars. Thus, we used
passenger vehicle acceleration rates for local streets. For conditions at the subject intersection, we
determined that approximately 5 seconds would be required to safely cross the thru street from the
side street. At 25 mph, a thru street vehicle would travel a distance of approximately 185 feet. Thus
the required sight distance would be 185 feet.
Positions of the stop vehicle, in our study, was also modified from AASHTO due to passenger car
dimensions and likely stopping locations. In this case, the drivers view from the stopped vehicle
would be 10' behind the curb line, or half of that require by AASHTO. The attached drawing was
done on MicroStation CADD and indicates the line of sight along with the geometric conditions of
this intersection. It can be seen that the difference in street widths on Fifth on each side of Third Ave
(9 feet) results in different lengths of parking restrictions. These calculations and measurements were
completed at every intersection in the study to insure that a minimum amount of parking had to be
removed. If strict adherence to AASHTO were followed, all parking on local streets would have to
be eliminated.
The reason for parking removal, to achieve safe sight distance, is not because of blind faith in design
standards. Moving vehicles follow the laws of physics by nature. If our streets or intersections do
not provide minimum dimensions to accommodate vehicle dynamics, we set up an inescapable trap
which is sprung every time two vehicles approximate the same location at the same time. The subject
intersection, as it exists, is a collision trap. Occurrence of accidents can be predicted based on the
probability of two vehicles approaching the intersection from right angles combined with the
probability that a vehicle is parked at a location which interferes with the line of sight. Since volumes
are relatively low, the probability of accidents is also low. However, the probability of avoiding a
collision, when these conditions occur, is essentially zero. Removal of parking will increase the
avoidance probability to something in excess of 90 percent.
Hopefully the above narratives and attached information have answered questions that were posed
to you. If I can be of any other service, please advise.
Sincerely,
Robert R. Marvin, P.E.
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