I-10 Twin Peaks Traffic Interchange, Environmental Assessment

Alternatives October 2005
Road). Prohibiting access in this area would minimize conflicts between low speed
vehicles turning into and out of driveways with traffic exiting and entering the interstate
at high speeds. The two-way circulation roadway around the west side of these properties
would allow properties near the Twin Peaks Road TI to access Twin Peaks Road directly
and I-10 and the frontage roads indirectly after frontage road access would be eliminated
(see access road in Figures 3-4A-C).
The alignment alternatives were presented to the businesses surrounding the proposed TI
on March 12 and 15, 2004 and to the general public on March 22, 2004. Almost no
support was expressed for the north alignment. Many participants stated a preference for
roadway alignments with fewer curves and a straighter alignment of Twin Peaks Road,
but no clear preference between the central and the south alignments was demonstrated.
The analysis of alternative alignments was documented in the Alternatives Selection
Report prepared for this project. Although readers are referred to the Alternatives
Selection Report for a more thorough discussion, the results of the analyses are
summarized here.
• The Center Alternative had the lowest construction costs.
• The Center Alternative required four fewer acres of additional right-of-way and
fewer total property takes.
• The Center Alternative exhibited the most desirable design characteristics.
• The Center Alternative exhibited the most favorable environmental
characteristics. These included:
� least visual affects;
� least displacement of habitat in the low flow and high flow channels of
the Santa Cruz River;
� least displacement of wetlands; and,
� avoided documented cultural resources.
As documented in the Alternatives Selection Report, the center alignment was selected to
be carried forward for detailed analysis in the EA and design phases of the project. This
alternative was selected because: it was the least cost alternative and minimized
additional right-of-way acquisition and total property takes; it exhibited the most
desirable design characteristics; it did not exhibit substantial disadvantages in comparison
to the north and south alignments; and, it was generally preferred by the affected property
owners and the public.
Subsequent to the selection of the center alignment as the preferred alignment, design
changes were required. The UPRR proposed to add a second track on the east side of the
existing track and to increase the elevation of the added track above that of the existing
track. In addition, revised traffic projections indicated that additional traffic lanes on the
bridge over the UPRR may be needed. As a result, the height of the bridge over the UPRR
was adjusted and the bridge width was increased to accommodate more traffic lanes at a
later time. These design changes made it impossible to “thread the needle” between the
UPRR tracks and the TEP towers. As a result, the relocation or the raising of one or more
of the transmission line towers would be required. However, relocation or raising one or
Interstate 10 Traffic Interchange at
Twin Peaks/Linda Vista
3-9
Project No.: NH-010-D (AIW)
TRACS No.: 10 PM 236 H5838 01D