Spack Memo 1-3-08
s ~ja.QJs
THE TRAFFIC STUDY COMPANY
Memorandum
To: Joe Shamla, City of Chanhassen
From: Mike Spack, P.E.
Date: 1/3/2008
Re: Traffic Review of Crossroads of Chanhassen
Per your request, I have reviewed the site plan and traffic study prepared by
Westwood Professional Services for the Crossroads of Chanhassen proposal. The
site is located on the northwest quadrant of the CSAH 18 (Lyman Blvd)/TH 101
intersection. The preliminary site plan and traffic report are both dated 12/14/07. My
findings are:
. The traffic report is professionally done using standard traffic engineering
methodology.
. Trip Generation: The data and calculations shown in Tables 2 through 6 of
the traffic study are correct. The number of vehicle fueling positions at the gas
station should be clarified. The traffic study assumes 10 vehicle fueling
positions (defined in the ITE Trip Generation Manual, ih Edition as the
maximum number of vehicles that could be simultaneously fueled). The
preliminary site plan appears to have 26 vehicle fueling positions. I briefly
spoke with Ryan Edstrom of Westwood and he indicated there will be 26
positions. If 26 vehicle fueling positions are proposed, the gas station would
generate approximately 4,000 gross vehicle trips per day instead of 1,530 trips
per day as indicated in Table 3 of the study. Westwood should provide you
updated trip generation tables for your public meetings if the 10 vehicle fueling
positions used in the calculations is incorrect.
. Trip Distribution: The trip distribution pattern in the study was based on the
traffic study prepared for the nearby Southwest Metro Transit Facility. This is
a reasonable approach; however no traffic was distributed on or off of the new
TH 212/TH 101 southern ramp intersection. The access to Crossroads of
Chanhassen on the northeast corner of the site forms the fourth leg of this
ramp intersection. The proposed development is oriented to take advantage
of its location at the interchange. I would expect a notable percentage of the
traffic using the site would be coming from or going to TH 212.
. External Intersections: The traffic study projected the site's turning movement
volumes at the CSAH 18/Site Road, TH 101/CSAH 18, and TH 101/TH 212
southern ramp intersections. This is an adequate scope for the traffic study
given the area road network was recently reconstructed. The TH 101
intersections were constructed with adequate turn lanes and traffic signals.
They are expected to operate acceptably with the addition of the site
Crossroads of Chanhassen
Traffic Review
20f3
Joe Sham/a, City of Chanhassen
generated traffic (even if the gas station traffic needs to be increased 2.6
times in the traffic study). The CSAH 18/Site Road intersection is
approximately 1/8 of a mile west of the TH 101/CSAH 18 intersection. CSAH
18 is designated as a class 5A Minor Arterial in Carver County's draft
transportation plan. Full accesses are allowed every % mile and traffic signals
are allowed at % mile spacing under this designation. A sensitivity analysis
was done for the CSAH 18/Site Road intersection using Carver County's
projection of 8,600 vehicles per day using CSAH 18 in 2030. It was assumed
the through volumes during the p.m. peak hour would be 10% of the daily
volume with 60% going westbound and 40% eastbound. The turning
movement volumes developed in the traffic study were used at the
intersection with an increase for the gas station traffic being 2.6 times higher.
With this worst case scenario, the southbound to eastbound left turn
movement will operate at Level of Service E with a maximum queue of six
vehicles calculated through a simulation with SimTraffic software. This
analysis suggests the CSAH 18/Site Road intersection will operate acceptably
well into the future, however the developer should be notified the intersection
does not meet the county's access spacing. If traffic volumes grow
significantly on CSAH 18, a traffic signal will be an unlikely solution for solving
backups at the intersection. The county would likely convert the intersection
to a % or right-in/right-out by blocking some of the turning and/or through
movements.
. Cut-throuQh Traffic: The internal site road will be a public street. It is
expected to attract some cut-through traffic from motorists trying to avoid the
CSAH 18/TH 101 intersection. The maximum daily traffic volumes on the
internal site road are expected to be approximately 4,500 vehicles per day
(6,000 vehicles per day if there are 26 vehicle fueling positions at the gas
station). The capacity of the road is approximately 10,000 vehicles per day
with the through lanes and turn lanes proposed at its access points on CSAH
18 and TH 101. At most, I do not foresee more than 2,000 of the 8,600
vehicles per day on CSAH 18 near the site in 2030 using the internal site road
as a cut-through. In a worst case scenario, the daily volumes on the road
should remain below its capacity. Again, the developer should be notified that
if a problem does arise at the CSAH 18/Site Road intersection the solution
would be to limit the intersection to a % or right-in/right-out. They have
chosen a roadway design that provides an attractive diagonal route and
having the access restricted could be a long term consequence.
· Roundabouts are becoming a viable traffic control measure and some believe
they discourage traffic. Roundabouts are not recommended for the proposed
development. They would require significantly more right-of-way and they
would not discourage traffic because there would not be enough cross traffic
at the driveways.
. Internal Intersections: It appears the internal roadway is designed for a 30
mph speed limit (which is mandated by the State Legislature), although
Westwood should provide horizontal and vertical curve dimensions to prove
the roadway meets current design standards. Sight distance standards need
to be met for the access driveways off of the internal site road. No objects
should be placed in the horizontal sight triangles at the intersections and the
Crossroads of Chanhassen
Traffic Review
30f3
Joe Sham/a, City of Chanhassen
roadway profile needs to provide enough vertical sight distance at each
intersection. I have several traffic related concerns about the northerly
driveway intersection on the internal site road, which provides access to the
gas station. (1) All-way stop sign control should not be installed at the
intersection as proposed. It will not meet the warrants for an all way stop sign
control per the Minnesota Manual on Uniform Traffic Control Devices. The
intersection would need 200 vehicles per hour, for eight hours, turning from
the gas station onto the internal site road to meet the warrants. (2) The
intersection appears to be at the bottom of a vertical crest, which could
provide sight line problems. (3) The natural delivery route for the gasoline
tankers would be from TH 212, which would force them to make almost a u-
turn maneuver either coming in or going out of the driveway. The driveway is
noticeably wider than the other proposed driveways, likely to accommodate
these turns. The wider driveway results in there being less positive control for
passenger vehicles, which could cause operational problems. (4) Vehicles
turning to the east out of the gas station parking lot go into a road that is two
lanes wide and then have to make a quick decision upon seeing the traffic
signal at TH 101. This situation could pose a safety problem with weaving
vehicles. (5) I developed several sets of turning movement forecasts for the
driveway intersection and simulated them in SimTraffic. It appears the
maximum queue would be five westbound vehicles. This would not spillback
to the intersection at TH 101, but there is potential for spillback if I grossly
underestimate the amount of cut-through traffic on the internal site road. For
these reasons, I recommend the northerly access be redesigned for the
gas station. There are many options to eliminate the traffic concerns,
including but not limited to: (1) take the "s" out of the internal site road with
two straight roads that meet at the northerly edge of the site with one curve or
(2) move the access south to the straight north/south portion of the road,
which would require "mirroring" the gas station layout to provide proper
access.
Please contact me at 952-378-5017 if you would like to discuss any of my findings.
Thank you for the opportunity to review the Crossroads of Chanhassen development
plan for the City.