HomeMy WebLinkAboutA002 - Council Action Form dated December 12, 2006 ITEM # Aa
DATE 12-12-06
COUNCIL ACTION FORM
SUBJECT: SPEED LIMIT ON SOUTH DAKOTA AVENUE
BACKGROUND:
City Council referred to staff a citizen's concern regarding the speed of traffic on South
Dakota Avenue. The request came from an employee who currently works at the Mary
Greeley Medical Center Hospice, located at 400 South Dakota Avenue. The citizen cited
difficulty when exiting from the site onto South Dakota.
The current speed limits for South Dakota Avenue are specified in Section 26.39(1)(o) of
Municipal Code in which there is a 25 mile per hour zone from Lincoln Way, south, to a
point 898 feet south of the center line of Todd Drive, and a 40 mile per hour zone from that
point, south, to the overpass with U.S. Highway 30.
When conducting research into the current regulations and background on South Dakota,
staff noted two particular projects that have significantly modified the dynamic of the
roadway. The first was the reconstruction of the Lincoln Way and South Dakota
intersection. As part of this project the first 900 feet of South Dakota, south of Lincoln Way,
was widened to 5-lane and 4-lane wide sections.
The second project widened South Dakota south of Todd Drive to the interchange with U.S.
Highway 30. This consisted of a 3-lane cross section from the northern extents of the
project to approximately Steinbeck Street, and at that point, a 5-lane cross section was
constructed to the project's southern terminus.
In response to direction from City Council, staff conducted a traffic engineering study in
which data was collected at two areas along the South Dakota corridor. The first location
was for the section of roadway abutting the intersection of Clemens Boulevard (the hospice
entrance). The second was for the section abutting the intersections of Todd Drive and
Lincoln Swing. Four main types of data were used to assess the traffic operations of the
corridor as follows: 85th Percentile Speed, Pace 2, ADT3, and Estimated Delay for Peak
Hour AM/PM4 (LOS) (see Attachment B for definitions).
The first study location consisted of an 8-day, 24-hour count, which was conducted near the
intersection of Clemens Boulevard from August 23, 2006, to August 30, 2006. A summary
for part 1 of this study has been shown in Table 1 (see Attachment A, Figures 1-4, for
respective time-of-day analysis).
Table 1
Part I Summary Results (Clemens)
: 1 . to 1 1 .
Northbound Southbound Units
85th Percentile Speed (40 mph limit) 38 38 mph
Pace (% of Population) 31 - 40 (83.40%)30 - 39 (78.14%) mph
Average Daily Traffic 5800 6500 veh.
Est. Peak Hour Delay AM,PM (LOS) 7.5(A) , 13.9(B) 9.7(A) , 15.0(C) I sec.
The average estimated delay a motorist may have to wait for a gap of the appropriate size
that would allow entering the traffic stream on South Dakota from Clemens Boulevard, the
hospice driveway and Cochrane Parkway is between 7.5 and 15 seconds (as shown in
Table 1). This maximum delay of 15 seconds is on the edge between level of service B and
C. Standard Council policy establishes a minimum level of service D for individual traffic
movements. The current situation far exceeds this standard. Therefore, traffic is able to
safely enter onto South Dakota Avenue within established parameters.
The second study location also consisted of an 8-day, 24-hour count, which was conducted
near the intersections of Todd Drive and Lincoln Swing from September 27, 2006, to
October 4, 2006. A summary for part 2 of this study has been shown in Table 2 (see
Attachment A, Figures 5-8, for respective time-of-day analysis).
Table 2
Part 11 Summary Results • • • • Swing)
1 . to 1 1 .
Northbound Southbound Units
85th Percentile Speed (25 mph limit) 40 35 mph
Pace (% of Population) 31 - 40 (67.15%)27 - 36 (72.62%) mph
Average Daily Traffic 6800 7100 veh.
S)
Est. Peak Hour Delay AM,PM (LO 10.0(A) , 18.8(C) 7.8(A) , 13.9(B) I sec.
Staff also conducted an analysis of the available departure sight distances at each of the
intersections within the study area. This procedure followed engineering standards as
specified in chapter 9 of AASHTO's "Green Book", which is the national standard for
geometric highway design. South Dakota Avenue is classified as a minor arterial.
In considering the results of this traffic study, staff came to the following
determination. The 40 mile per hour zone is the appropriate speed limit for the
southern portion of South Dakota Avenue. The data collected supports the 40 mile
per hour designation based upon the propensity of motorists to travel this speed in
relation to the geometric design of South Dakota as a minor arterial. Whereas, the
data suggests that the 25 mile per hour zone along South Dakota (approximately the
first 1500 feet south of Lincoln Way) is not supported by either the
roadway/intersection design or by prevailing driver behavior.
Therefore, it is the recommendation of staff to retain the 40 mile per hour designation as it is
currently defined in Municipal Code, and amend the section pertaining to the 25 mile per
hour zone such that it is increased to a more appropriate speed limit of 35 miles per hour. It
should be noted that the retaining of two separate speed zones is reflective of the available
sight distances at the Todd Drive and Lincoln Swing intersections.
A flashing yellow light was installed a number of years ago as the designated school route
crossing at Todd Drive. Part of the community's efforts during the consolidation of the City
of Ames elementary schools was to redefine the suggested routes to school. In response to
the final approved routes, the flashing yellow light and 20 mile per hour speed limit sign
apparatuses were removed. It was decided that students traveling to school should walk
along South Dakota and cross at either the Lincoln Way or Mortensen Road traffic signals.
At this time staff would also recommend removal of Section 26.39(1)(o) of the
Municipal Code pertaining to the 20 mile per hour zone, which applied only when
flashing yellow lights were installed and in operation.
ALTERNATIVES:
1. Direct the City Attorney to modify the ordinance to change the speed limits along South
Dakota Avenue, by establishing a 35 mile per hour zone for the first 1500 feet south
from the centerline of Lincoln Way, and a 40 mile per hour zone from that point, south,
to the overpass with U.S. Highway 30. This action will also initiate an ordinance change
to remove the reference to a special 20 mile per hour zone at Todd Drive.
2. Direct staff to lower the speed limits along South Dakota Avenue. However, this likely
would not result in greater available gaps. Setting speed limits lower than the speed at
which drivers feel they may safely operate would likely lead to vehicles bunching
together, which may reduce available gaps.
3. Direct staff to explore other alternatives.
4. Do not change the speed limits on South Dakota Avenue.
MANAGER'S RECOMMENDED ACTION:
The recommended changes to the speed limits on South Dakota Avenue are intended to
enhance traffic operations of the entire South Dakota corridor. These updated regulatory
designations would be reflective of the current roadway dynamic and may in turn help to
foster proper compliance with the posted speed limit. The speed data collected shows the
40 mile per hour speed limit is appropriate and the 25 mile per hour section should be
raised to 35 miles per hour. This data is also reflected in driver behavior through the
corridor.
Therefore, it is the recommendation of the City Manager that the City Council adopt
Alternative No. 1, thereby directing the City Attorney to modify the ordinance to change the
speed limits along South Dakota Avenue, by establishing a 35 mile per hour zone for the
first 1500 feet south from the centerline of Lincoln Way, and a 40 mile per hour zone from
that point, south, to the overpass with U.S. Highway 30. This action will also initiate an
ordinance change to remove the reference to a special 20 mile per hour zone at Todd Drive.
ATTACHMENT A: LIST OF FIGURES
Part I: Data taken near Clemens Boulevard Intersection (8/23/06 to 8/30/06)
Northbound Data Near Clemens Boulevard
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Figure 1
Southbound Data Near Clemens Boulevard
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Figure 2
(Continued from previous page)
Estimated Average Delay: Northbound Near Clemens Boulevard
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Figure 3
Estimated Average Delay: Southbound Near Clemens Boulevard
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Figure 4
Part II: Data taken near Todd Drive and Lincoln Swing intersections
Northbound Data Near Todd Drive/Lincoln Swing
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Figure 5
Southbound Data Near Todd Drive/Lincoln Swing
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Figure 6
(Continued from previous page)
Estimated Average Delay: Northbound Near Todd/Lincoln Swing
20
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Figure 7
Estimated Average Delay:Southbound Near Todd/Lincoln Swing
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ATTACHMENT B: DEFINITION OF KEY TERMS
1 . 85th Percentile Speed: Is defined as the speed at which 85% of vehicular traffic
is traveling, or slower.
2. Pace: Is the 10 miles per hour range that the largest number of vehicles is
traveling in.
3. Average Daily Traffic (ADT): Is the total daily average volume of traffic as
taken over the extent of the study.
4. Estimated Peak Hour Delay AM/PM: This value is the average estimated
delay, in seconds, a motorist may have to wait for a gap of the appropriate size
that would allow entering the traffic stream on the major roadway from a side
street approach.
5. Level of Service: Is a unit of measure that assesses the operational health of
an intersection or approach as specified in the 2000 Highway Capacity Manual
(HCM) base upon averaged control delay. A table from the HCM has been
provided below.
Table 1:HCM,4th Addition,Exhibit 17-2 17-2
Level of Service Criteria for TWSC and AWSC
intersections 100
LOS Control Delay Per Vehicle(sec)
A <10
B >10 and <_15
C >15 and _<25
D >25 and <_35
E >35 and <_50
F >50
TWSC=Two Way Stop Control
AWSC=All Way Stop Control
ATTACHMENT C: EXISTING AND PROPOSED SPEED LIMITS
Lincoln Way —
C
20 MPH Zone (Flashing Yellow);
(Proposed Removal) NOT TO SCALE
10
60
25 MPH Zone;
(Proposed 35 MPH Zone)
Clemens Boulevard o
a�
Mary Greeley
CD
Q Medical Center
Hospice
Y Driveway
M
0
t
0 R
40 MPH Zone
o/'enSen Road ° o0 0