HomeMy WebLinkAbout2018-11-18 ACHD Traffic Impact Studys
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November 28, 2018
Brett Korporaal
Kittelson & Associates
101 S. Capitol Boulevard, STE 301
Boise, ID 83702
Subject: ICCU Plaza Traffic Impact Study
Sara M. Baker, President
Rebecca W. Arnold, Vice President
Jim D. Hansen, Commissioner
Kent Goldthorpe, Commissioner
Paul Woods, Commissioner
The Ada County Highway District (ACHD) staff has completed an initial review of the
submitted traffic impact study (TIS) for the proposed ICCU Plaza Development.
Comments/recommendations provided by District Traffic Services and Planning Review
staff are listed below:
1. Staff does not recommend the construction of a westbound right turn lane at the
intersection of Overland Road and Rackham Way at its current location. If Rackham way
is relocated to the east in the future a westbound right turn lane should be installed at
that time.
2. The overview of existing conditions on pages 29 and 30 recommend increasing the PM
Peak cycle length at the traffic signals at the intersections of Eagle Road & Overland
Road and Eagle Road & the 1-84 westbound ramps from 140 seconds to 160 seconds
for existing conditions. This is not included in the Executive Summary, but the summary
does include recommendations to increase the cycle length at Overland Road &
Silverstone Way from 140 seconds to 160 seconds for 2020 total traffic.
The recommendation to increase the cycle length at these traffic signals is not realistic.
These signals are part of a complex coordinated system including other signals to the
east and to the west on Overland Road and to the north and south on Eagle Road.
During the PM peak, all signals included in this system, which extends as far north as
McMillan Road and as far east as Cole Road, operate with the same cycle length or
multiples of the same cycle length (70 seconds, 140 seconds, or 210 seconds).
Increasing the cycle lengths at a few intersections to 160 seconds would remove them
from the existing coordination plans and would be disruptive to traffic flow along
Overland Road and Eagle Road.
A cycle length of 210 seconds at the intersection of Eagle Road & the 1-84 westbound
ramps was determined to be undesirable during the last re -timing efforts along Eagle
Road. The coordination plans on Eagle Road will be revisited in approximately 2020 and
all signals in question will certainly be retimed at least once prior to 2030. Based staff's
knowledge of the existing operations significant cycle length changes are not anticipated
in the near future.
Ada County Highway District • 3775 Adams Street • Garden City, ID • 83714 • PH 208-387-6100 • FX 345-7650 • www.achd.ada.id.us
Coordinated traffic signal operations are constrained by the needs of the network as a
whole rather than individual intersections. All analysis should reflect the existing cycle
length constraints.
3. The southbound leg of the intersection of Eagle Road and Overland Road is owned by
ITD. The intersection should also be analyzed without improvements to this leg per
ACHD Policy.
4. The westbound approach of the intersection of Eagle Road & Overland Road currently
has a single exclusive right -turn lane, a shared thru/right-turn lane, an exclusive through
lane, and an exclusive left -turn lane. For all scenarios including the existing lane
configuration, the shared thru/right-turn lane was analyzed as an exclusive through lane.
The analysis needs to be corrected for all scenarios. Staff recommends that this lane be
analyzed as an exclusive through lane for all future scenarios that include additional right
turn lanes.
5. Staff recommends extending the eastbound left turn at Overland Road & Silverstone
Way to increase storage while avoiding interference with the driveway to the west.
However, staff cannot find the specific trigger for this improvement in the TIS.
Please let me know if you have any questions.
Sincerely,
Mindy Wallace, AICP
Planner III
Development Services
CC: Spink Butler - Geoff Wardle
Ada County Highway District • 3775 Adams Street • Garden City, ID • 83714 • PH 208-387-6100 • FX 345-7650 •
www.achd.ada.id.us