09-05-08 City Comment Response LetterMEMORANDUM Date: September 4, 2008 Re: Chanhassen Medical Office Development Traffic Study File 20061094 To: City of Chanhassen Planning Department From: Bruce Boje Nicholas J. Erpelding,
P.E., PTOE In response to your July 15th, 2008 comments regarding Westwood’s July 3rd Traffic Study, we offer the following responses. Comment 1: Update traffic counts to current county
estimates. Get traffic model from Carver County. ADTs from MNDOT were used in the model. Response: Westwood contacted Mr. Roger Gustafson with Carver County to request the most recent
estimates on Tuesday, July 29th. After following Mr. Gustafson’s direction to contact SRF Consulting Group, a response was received from SRF as follows: Please find the attached scan
with forecast volumes from the Carver County Transportation Plan. As you will see, only one volume is given on Powers in your study area, and would apply to the entire segment between
Lyman and Pioneer. The volumes shown here represent the preferred scenario for the County plan, wh?ich is the "State + County Improvements". Other scenarios include forecasts ranging
from 18,000 to 21,000 vpd on Powers in this location. Please note that these forecasts do not take into consideration two significant land uses near this site: 1) the new high school
being built on the north side of Lyman just west of Audubon, and 2) a proposed shopping mall near the intersection of Lyman and Powers. I hope this information helps. Please let me know
if anything else comes up. Paul Paul Morris Transportation Engineer SRF Consulting Group, Inc. Along with the following sketch:
September 4, 2008 Page 2 Figure 1: SRF/Carver County Preliminary 2030 ADT forecasts As noted by SRF, the ADT forecasts completed are general in nature, with only one ADT forecast for
the entire Powers Boulevard segment from Lyman Boulevard on the north to Pioneer Trail on the south. (It should also be noted that these preliminary
September 4, 2008 Page 3 forecasts do not yet appear to have been formally published as part of the County’s Comprehensive Plan update.) The SRF forecast of 19,600 ADT for this segment
of Powers Boulevard in 2030 appears consistent with the Westwood’s projected year 2020 ADT range of 16,900 to 21,800 shown on Figure 8 of the report. ---Comment 2: Traffic report states
that a traffic signal is required. Carver County spacing guidelines are not met at this location. Discussions between MnDOT, Carver County, and the City are needed to see if a traffic
signal can be installed at this location. Response: The 2003 Kimley-Horn Chanhassen AUAR includes no discussion of the operations of this intersection. The report does indicate on Figure
11 that side street stop control is proposed for the intersection, which was analyzed as a “T” intersection (the 4th/east leg was not included). Westwood’s July 3rd traffic report notes
that based solely on level of service, a traffic signal would be required concurrent with Phase 2 development in order to prevent the exiting left turn movement from dropping to an unacceptable
LOS. Though the comment was made that a traffic signal would be “required,” it was made with the understanding that one would not be installed until it was fully warranted and justified.
In the metro area, it is common for a side street stop controlled intersection to operate with failing side street movements during peak times. Such intersections can and do remain side
street stop controlled indefinitely. The appropriate course of action is to monitor the intersection as traffic volumes grow to determine if and when changes in intersection control
should be made. To further assess when traffic volumes at the intersection might necessitate installation of a traffic signal, additional analysis was undertaken. The turning movement
volumes forecasted in the report were compared with the traffic volume warrants for the installation of a traffic signal identified in the current Minnesota Manual on Uniform Traffic
Control Devices (MnMUTCD).
September 4, 2008 Page 4 Table 1 Warrant Analysis Summary Warrant Hours Required: Hours Met: 2010 No-Build 2010 Build 2012 Build 2020 Build (Phase 1) (Phase 2) Phase 3a Phase 3b 1A 8
2 2 2 2 2 1B 8 7 7 7 7 7 1C 8 1 1 1 1 1 2 4 6 6 6 6 6 3 1 4 5 5 5 5 Assumptions: 1. Based on peak hour volumes in July 3, 2008 Traffic Analysis Report 2. Hourly variation assumed from
MnDOT ATR 458 (2007 volumes). 3. Right turn volumes excluded. 4. 0.70 factor applied (located on high speed roadway -40 MPH+). 5. 2+ approach lanes for both Powers Boulevard and Site
Collector Roadway. The results documented in Table 1 show that the amount of traffic contributing toward the fulfillment of signal warrants remains nearly constant as development of
the subject site proceeds from vacant through full build. This is explained by the fact that the primary generator of traffic contributing toward fulfillment of signal warrants is development
to the west of Powers Boulevard, not development on the subject site. (As is noted in the response response to comment 3, below, full development of the Chanhassen AUAR site to the west
of Powers Boulevard was assumed by 2010.) To further assess what contribution traffic from the subject site has toward fulfillment of signal warrants, the analysis was updated with the
assumption that the site to the west remains vacant. With this assumption, in contrast, the number of hours each warrant is met increases as development proceeds. At full build out,
the number of hours for which warrants are met is just below that of the 2010 No-Build scenario in Table 1. This confirms that traffic from the subject site is not the primary contributor
to the need for signalization.
September 4, 2008 Page 5 Table 2 Warrant Analysis Summary – No development west of Powers Boulevard Warrant Hours Required: Hours Met: 2010 Build 2012 Build 2020 Build (Phase 1) (Phase
2) Phase 3a Phase 3b 1A 8 0 0 2 0 1B 8 0 4 7 4 1C 8 0 0 0 0 2 4 0 2 6 3 3 1 0 1 4 2 Assumptions: 1. Based on peak hour volumes in July 3, 2008 Traffic Analysis Report 2. Hourly variation
assumed from MnDOT ATR 458 (2007 volumes). 3. Right turn volumes excluded. 4. 0.70 factor applied (located on high speed roadway -40 MPH+). 5. 2+ approach lanes for both Powers Boulevard
and Site Collector Roadway. 6. Assumes no adjacent development west of Powers Blvd. It is further noted that in the metro area, an intersection must typically meet more than one warrant
in order justify installation of a traffic signal. This is due to in part to delay increasing for the mainline and the increased potential for mainline rear end collisions. Based on
the analysis completed, traffic volumes at the intersection will be close but may not fully justify installation of a traffic signal through full build out of the site in 2020. Noting
that a signal was forecast to be necessary in terms of level of service concurrent with Phase 2 in 2012, the intersection would be expected to operate at poor LOS during peak times with
good LOS the remainder (and majority) of the day. Access Spacing The intersection of Powers Boulevard and Site Collector Roadway does not meet the prescribed full access spacing of ¼
mile along Powers Boulevard, as identified on the figure on page 4.39 in the most current version of the Carver County Comprehensive Plan. With approximately 820 feet of spacing provided,
center-to-center, it falls 500 feet, or 38% short. It is Westwood’s understanding that the location of this intersection was selected during design of the TH 212 project to best fit
with the natural topography and wetland constraints. While it is true that full ¼ mile spacing is not met at the chosen location, it represents a workable compromise location. Without
having completed a formal analysis of the corridor, but based on experience with similar situations, it is
September 4, 2008 Page 6 anticipated that signal timing and phasing plans can be developed to accommodate the selected intersection location without compromising the operational integrity
of the Powers Boulevard corridor. Other noteworthy considerations include the fact that the Site Collector Roadway intersection is the only intersection proposed in the roadway segment
between the TH 212 south ramps and Pioneer Trail just under ½ mile to the south feet to the south. Because this segment is less than ½ mile in length, no access location will be able
to provide the necessary full ¼ mile spacing required on both resulting segments. Finally, a 4-lane roadway section with turn lanes such proposed for this stretch of Powers Boulevard
is typically capable of carrying over 40,000 ADT. 2030 volume forecasts are in the 20,000 ADT range, meaning a substantial capacity cushion is likely to exist. ---Comment 3: Development
will occur on the opposite side of this proposed access road. Has this been taken into account in in the traffic report? If so, what are your assumptions? Response: As noted on page
1 of the Westwood Traffic Report, “The Chanhassen 2005 Alternative Urban Area-Wide Review (AUAR) prepared in 2003 for the City of Chanhassen by the consultant team of Hoisington Koegler
Group Inc., Kimley Horn and Associates, Peterson Environmental Consulting, 106 Group and HDR was used in the determination of background traffic volumes and traffic assignment process.”
Full build of the Chanhassen AUAR area was assumed by 2010, as assumed in the Chanhassen AUAR. The turning movement volume illustrations, Figures 5-8, reflect this assumption. ---Comment
4: What happens to the intersection on the Highway 101 side in the year 2020 when this area is fully developed? Response: The traffic study completed is intended to provide support for
Phases 1 and 2 of the proposed development only. This includes the two medical office buildings located immediately adjacent to Powers Boulevard south of the TH 212 ramps. Consideration
of development of a Phase 3 was done only to gauge anticipated future traffic conditions at intersections impacted by Phase 1 and 2 development, not to provide a full analysis of the
impacts of Phase 3 development.
September 4, 2008 Page 7 Due to the small magnitude of development proposed for Phases 1 and 2, a full analysis of the impacts of the extension of the site collector roadway to CSAH
101 was not undertaken. The report does note (in Figure 4) that only 5% of the site generated traffic from the subject medical office site is forecast to use the extension to connect
to CSAH 101. This 5% would amount to fewer than 300 trips per day, well below the often-used 1,000 ADT minimum threshold for detailed study. It is anticipated that detailed study of
the Site Collector roadway extension to CSAH 101 will be completed at the time formal development plans for Phase 3 are put forth.