HomeMy WebLinkAbout29B COB Memorandum MORRISON
JA MAIERLE,INC. memo
TO: Bob Murray, P.E.
City of Bozeman
FROM: Bill White
DATE: February 26, 2015
JOB NO.: 5352.003
RE: The Lakes at Valley West, Supplemental TIS Analysis and Threshold Study
CC: Greg Stratton
❑Urgent ®For Review ®Please Comment ®Please Reply
p y ❑For Your Use
This memorandum summarizes a supplemental analyses provided in support of the Lakes at
Valley West Traffic Impact Study (TIS), submitted to the City of Bozeman in February 2015.
This analysis was developed to confirm the timing of improvements for the Cottonwood
Road/Durston Road intersection. Also, this study recommends a phased approach for
improving capacity at the Laurel Parkway/Durston Road intersection over those recommended
in the original TIS given understanding of current regional plans within the Valley West
neighborhood. Please review and contact our office with questions and/or comments.
1. PURPOSE OF MEMORANDUM
The Lakes at Valley West TIS was submitted to City of Bozeman Engineering officials earlier
this month (February 2015). The analysis identifies the transportation impacts of the proposed
development on adjacent and nearby City arterials and roadways; confirming regional
improvements that the Bozeman Engineering staff recommend to address forecasted traffic
growth for Durston Road and identifying "fair and proportionate" project mitigations/participation
towards these improvements.
Through coordination prior to TIS submittal, it was determined/established that City Engineering
officials desired to promote a three lane roadway section along Durston Road between
Cottonwood Road and Westgate Avenue (approximately 4,000 feet) as a regionally beneficial
improvement for the future Valley West neighborhood. By extension, City officials indicated the
development of roundabouts or traffic signals were preferred as the control measure for busy
intersections; most specifically for the Cottonwood Road/Durston Road intersection. Section 6.2
of the TIS describes:
`A number of improvements are planned by City of Bozeman Engineers. These
improvements were vetted by this study, and confirmed for both study intersections. The
following measures were proposed to address capacity/operational issues, with project
participation, to include:
< A traffic signal or roundabout is confirmed and recommended for the Durston
Road/Cottonwood Road intersection, which is projected to experience unacceptable
LOS by year 2016. din interim, all/four way stop can be developed to promote LOS
for two additional years. However, the signal improvement would ultimately be
required by year 2018, and would fully address operational issues at the intersection
(promoting LOS BIC traffic operations). The project would have an 11.6% growth
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impact and recommended proportionate responsibility towards intersection
improvements.
A two-way left-turn lane (center turn lane) is confirmed along Durston Road between
Cottonwood Road and Westgate Avenue. The analysis of the Laurel
Parkway/Durston Road intersection indicates this improvement would be needed by
year 2020 to address LOS issues. The TWLTL would promote a LOS DIE function
for this intersection, as well as improve traffic operations for other intersections and
driveways along Durston Road. The project would have an 17.1% growth impact and
recommended proportionate responsibility towards Durston Road widening
improvements.
c Alternatively, a roundabout or signal could be constructed for Laurel
Parkway/Durston Road if City Engineers determine the TWLTL is not the appropriate
solution for the intersection. This focused improvement would elevate operations
back into the LOS B range; however, this would not offer the benefit of the TWLTL
for the remainder for Durston Road. The project would have an 17.7% growth
impact and recommended proportionate responsibility towards intersection
improvements, if a signal were selected over the TWLTL."
Purpose: An analysis was performed to identify "thresholds" when improvements would be
required for the Cottonwood Road/Durston Road intersection to maintain a LOS C standard.
This memorandum has been developed principally to provide this information as supplemental
information to the TIS.
In addition, the potential for a roundabout or traffic signal was identified in the original TIS for the
Laurel Parkway/Durston Road intersection as a stand-alone improvement; despite industry
guidance to resist such improvements along arterials at local streets. This was made as a
capacity and safety improvement without anticipation regarding the availability of additional
east-west access roadways within the Valley West neighborhood; redistributing the heavy
southbound-left turn volumes causing LOS issues at this intersection. Thus, this memorandum
recommends an alternative improvement to a roundabout or signal, as a short-term measure
which could be later removed, until the capacity offered by these alternative routes is available.
2. ANALYSES AND RECOMMENDATIONS
The approach to traffic forecasting and capacity/operations analysis is fully documented in the
Lakes at Valley West TIS, which should be reviewed in context to this follow up study. The
purpose of this supplement was to review the phased development of the project proposal,
identifying the specific improvements needed to mitigate project impacts. The goals of
supplemental analyses were to:
1. Assure improvement recommendations fully mitigate project impacts, as measured
based on phases comparisons of future without versus future with project traffic
operations/capacity (levels-of-service and average control delays);
2. Assure a level-of-service C performance measure could be achieved with the
recommendation of such improvements, thus assuring public safety;
3. That recommended improvements could be established as "building blocks" towards the
regional improvement plans promoted by Bozeman Engineers (i.e. a first improvement
action that could be used towards ultimate completion of regional improvements).
As indicated by the TIS, the Lakes at Valley West would include up to 300 dwelling units
developed on 65 acres aligned south of Durston Road and '/4 mile west of Cottonwood Road.
The project would be constructed over approximately 10 years; averaging the construction of 24
single family and 36 multifamily homes every two years.
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For this supplemental analysis, traffic forecasts were developed every two-years to review
project impacts and determine improvement mitigation (year 2016, 2018, 2020, 2022, and 2024,
respectively). As with the TIS, two forecast methodologies were used to address a potential
range of future traffic conditions (alternative volume scenarios within the City, with
methodologies generally summarized as follows:
< Growth Rates. Future without project traffic forecasts were developed using a 3-
percent annual growth rate to the phased analysis year. Phased project trip
assignments, as generated by an incremental 60 single and multi-family homes every
two years, were combined with future without project forecasts to generate future with-
project traffic forecasts for the peak AM and PM peak analysis timeframes.
Pipeline Projects. A 1 percent annual growth rate plus the trip assignments generated
by approved, but yet to be developed, "pipeline" development projects, were used to
develop future without project forecasts. An incremental 20% of pipeline project trip
assignments were applied every two years with this phased approach for the 2016,
2018, 2020, 2022, and 2024 horizon years. Phased project trip assignments, as
generated by an incremental 60 single and multi-family homes every two years, were
combined with future without project forecasts to generate future with-project traffic
forecasts for the AM and PM peak analysis timeframes.
Four existing intersections and one new intersection were reviewed with the TIS for the Valley
West neighborhood. Two forecast deficiencies were identified for the Cottonwood
Road/Durston Road and Laurel Parkway/Durston Road intersections, for which mitigation was
identified in the original report. This addendum addresses traffic forecasts, traffic
operations/capacity (LOS), and proposes specific mitigation improvements for these
intersections specifically given the LOS exceptions.
A table of resulting LOS for the "growth" and "pipeline" forecast analysis conditions is attached
to this technical memorandum. This table identifies future without and with project LOS and
delays for the purpose of identifying the phased impacts of project development (as measured
in LOS and delay). The improvements needed to mitigate project impacts and maintain LOS C
standards was then provided for the 2016, 2018, 2020, 2022, and 2024 horizon years, with the
resulting LOS and delay gains also provided for the AM and PM peak hours of the typical
weekday.
The following discussion provides summary improvement results for each intersection, followed
by a threshold analysis that identifies improvement needs by development phase and horizon
year, as referenced to the attached LOS and delay table. Summary LOS worksheets and traffic
forecasts can be provided upon request.
Cottonwood Road/Durston Road. The Cottonwood Road/Durston Road intersection
currently functions at LOS E, which is a preexisting condition below the LOS C
operations/capacity thresholds identified in Sec. 38.24.060 of City of Bozeman "Unified
Development Code". Thus, improvements are needed immediately to assure capacity and
safety for the intersection.
This is an intersection between two arterials and, as such, a roundabout or traffic signal is
appropriate long term improvement options for the intersection. However, time is needed for the
City and development community to generate the capital needed to construct one of these
improvements, with a present budget estimate of$750,000 maintained by City Engineers for the
project. As such, the TIS and this supplemental analysis confirms that a four-way stop with the
progressive development of turn lanes can be used to promote the desire LOS needed to
assure capacity and safety until funding is secured by year 2019.
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LaureV Parkway/Durston Road. A two-way left-turn lane (TWLTL) was confirmed to help
facilitate turning movements at current and future intersections along Durston Road. However,
there are left-turning conflicts that can evolve within a TWLTL over time (with the growth of
traffic) at four-leg intersections, such as the SBL and WBL at Laurel Parkway/Durston Road.
For this reason, the TIA reviewed the potential for a roundabout or signal at the Laurel
Parkway/Durston Road intersection as a stand-alone improvement to address a LOS issue
noted as the result of high southbound left-turn movements.
The recommendation was made without anticipation of roadways extensions, such as Oak
Street, Annie Street, and possibly Sherwood Way to Cottonwood Road (and beyond) as the
timing of full maturation of the Valley West neighborhood was unknown. However, it is
understood the extension of these roadways may be more imminent as the pace of residential
development is increasing in Bozeman, and therefore these roadways would be complete as
frontage improvements of the development community sooner than initially anticipated by the
TIS. The availability of these roadways would redistribute traffic from the critical southbound
left-turn movement at Laurel Parkway/Durston Road, which is the cause of the LOS issue at the
intersection; promoting travel through the local street network. Traffic would to turn right on
arterials such as Cottonwood Road and then protected left turns can be performed on Durston
Road via signalized intersections such as the one proposed at Cottonwood Road/Durston Road.
In addition, Laurel Parkway will be extended to Babcock Street and eventually Hoffine Lane and
this will help redistribute south, further reducing traffic demands on the Laurel Parkway/Durston
Road intersection.
The promotion of a roundabout or signal at local street, or even a future collector, is less
desirable as they can impact the efficiency/capacity of an arterial and is not typically
recommended in documents such as the Access Management Manual (TRB, 2003), the Urban
Street Geometric Design Handbook (ITE, 2008), and even A Policy on Geometric Design of
Highways and Streets (ASSHTO, 2011). The recommendation was appropriate within the
context of the unknown timing of east-west connectivity. However, given the more immediate
availability of east-west roadways, the recommendation of a signal/roundabout is less preferred.
Thus, this supplemental analysis alternatively recommends a four-way stop at Laurel
Parkway/Durston Road as a temporary improvement used until east-west connectivity and the
redistribution of these southbound lefts can occur in the future. As discussed in the threshold
discussions below, this improvement would promote LOS C operations at the intersection
through year 2024. The four way stop can be removed as alternative travel routes reduce traffic
volumes and capacity demands of the intersection.
The remaining discussion provides a threshold timeline review of improvements on a bi-annual
basis, used in helping to plan improvements for the study area.
Year 2016 - 60 Units
The analysis indicates moderate LOS deficiencies for the Laurel Parkway/Durston Road and
Cottonwood Road/Durston Road intersections. The following improvements would be needed
to promote traffic operations to LOS C at these intersections in year 2016:
Cottonwood/Durston Road. A four-way stop with an eastbound right-turn lane.
4 Laurel Parkway/Durston Road. A four-way stop.
Year 2016 - 120 Units
The analysis indicates LOS deficiencies for the Laurel Parkway/Durston Road and Cottonwood
Road/Durston Road intersections. The following improvements would be needed to promote
traffic operations to LOS C at these intersections in year 2018:
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Cottonwood/Durston Road. A four-way stop with an eastbound right-turn lane and
westbound left-turn lane.
♦ Laurel Parkway/Durston Road. A four-way stop.
Year 2020 - 180 Units
The analysis indicates LOS deficiencies for the Laurel Parkway/Durston Road and Cottonwood
Road/Durston Road intersections. The following improvements would be needed to promote
traffic operations to LOS C at these intersections in year 2020:
< Cottonwood/Durston Road. A two-phase traffic signal with an eastbound right-turn
lane and westbound left-turn lane, removing four-way stop. "Pucks" or video detection
can be used for actuation purposes to avoid cutting existing pavement for advanced
detection (via loops).
Laurel Parkway/Durston Road. A four-way stop.
Year 2022 - 240 Units
The analysis indicates LOS deficiencies for the Laurel Parkway/Durston Road and Cottonwood
Road/Durston Road intersections. The following improvements would be needed to promote
traffic operations to LOS C at these intersections in year 2022:
< Cottonwood/Durston Road. A two-phase traffic signal with an eastbound right-turn
lane and westbound left-turn lane. "Pucks" or video detection can be used for actuation
purposes to avoid cutting existing pavement for advanced detection (via loops).
♦ Laurel Parkway/Durston Road. A four-way stop.
Year 2024 - 300 Units
The analysis indicates LOS deficiencies for the Laurel Parkway/Durston Road and Cottonwood
Road/Durston Road intersections. The following improvements would be needed to promote
traffic operations to LOS C at these intersections in year 2024:
< Cottonwood/Durston Road. A two-phase traffic signal with an eastbound right-turn
lane and westbound left-turn lane. "Pucks" or video detection can be used for actuation
purposes to avoid cutting existing pavement for advanced detection (via loops).
< Laurel Parkway/Durston Road. A four-way stop.
Again, we encourage you to contact us with questions and/or comments regarding this
supplemental analyses performed in support of the Lakes of Valley West TIS submitted earlier
this month to the City of Bozeman.
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