Appendix D Traffic Impact Analysis - westplainseis.com

overall site plan would not be significantly altered and the proposed size and type of land uses (and
therefore trip generation) would remain the same.
The revised access scheme was analyzed for all site plan Alternatives 1-3 and Phasing of Alternative 1
consistent with the approach and assumptions in the TIA. Global trip distribution assumptions were not
altered. Trip assignment to HWY 2 was adjusted to account for the change in access scheme but the total
entering/exiting traffic to/from HWY 2 related to the subject site development remains consistent with
the TIA. Volume assumptions are included as an attachment.
For 2032 Cumulative conditions a fourth, southerly leg of the westerly roundabout intersection was
added and some traffic generated southbound left turn volumes were shifted to the southbound through
movement utilizing the southerly leg of the roundabout.
The analysis indicates that both roundabout access intersections will function at acceptable levels of
service for all analysis scenarios. The LOS results are summarized in Attachment B and analysis output
reports are included in Attachment C.
Additionally, the HWY 2/Craig intersection was reanalyzed under 2032 Cumulative Alt. 1 conditions;
the TIA indicated a LOS F for this location and analysis scenario. With the revised access scheme and
inclusion of the southerly 4 th leg at the westerly access to provide a connection and alternative route to
21 st Ave., the project related trips at HWY 2/Craig are reduced. Furthermore, modifications were made
to the assumed roundabout geometry at HWY 2/Craig to include dual left turn movements for the NB
and SB approaches. With these revisions, the analysis indicates an acceptable LOS of LOS with an
average delay of 54.4 secs. Analysis output reports and geometry figures are attached.
Roadway Connectivity
Reasonable local connectivity and connectivity to adjacent arterial roadways can be achieved with the
internal roadway network proposed and originally proposed access location as well as the recently
proposed Two Roundabout Access scheme. Access and connectivity for the site south of HWY 2 across
from the subject site can achieved through the addition of a 4 th leg of the middle roundabout access to the
Spokane Tribe site.
A southerly leg of the westerly roundabout intersection could ultimately extend south to connect to the
future of 21 st Ave. extension which will serve as an alternative east/west regional route and relieve traffic
congestion on the HWY 2 corridor.
The roundabout site access located at the westerly boundary of the Spokane Tribe could provide access
to a future North-South road located along the westerly Spokane Tribe property line; this road would
provide access to the area and sites west of the Spokane Tribe site as well as connectivity to a future
extension of 6 th Ave.
Cumulative (2032) Condition Corridor Impacts
The West Plains-Spokane International Transportation study (WP-SIA, SRTC May, 2011) reviewed
corridor congestion impacts for a study area that includes the study area of the Spokane Tribe TIA as
well as areas outside of the Spokane Tribe TIA study area. The travel demand modeling completed for
this study contemplated and included development of the Spokane Tribe’s subject parcel therefore the
volumes associated with proposed project and thpg eir presence and impact on the regional roadway
network are reflected in the study. Various project alternatives were developed to address future corridor
capacity deficiencies.
The WP-SIA study included a menu of improvements many of which are well outside the study area of
the Spokane Tribe TIA and some alternatives were deemed undesirable upon full evaluation and
West Plains Development – Spokane Tribe Page | 2
Traffic Impact Analysis Addendum July 18, 2011