HEX Rsp to Third Continuance-Part 4 101014
2802 Wetmore Avenue Suite 220 Everett WA, 98201
Tel: 425-339-8266 Fax: 425-258-2922 E-mail: info@gibsontraffic.com
MEMORANDUM
To: Alan Wallace, Williams Kastner
From: Brad Lincoln, PE
Subject: Rolling Sunrise – Traffic Impact Review
Date: October 10, 2014
Project: GTC #14-226
Gibson Traffic Consultants, Inc. (GTC) has been retained to review the traffic impacts of the Rolling
Sunrise development. The review includes reviewing the need for a traffic impact analysis and
analyzing the adequacy of the surrounding roadways to handle the traffic generated by the
development.
1. BACKGROUND
The Rolling Sunrise development is located in the City of Bainbridge Island between Hyla Avenue
NE and the intersection of Sunrise Drive NE at NE Duncan Lane. The development is currently
proposed to consist of 7 total units. The development is proposed to have 4 units access Sunrise Drive
NE and have 3 units access Hyla Avenue NE.
2. NEED FOR A TRAFFIC IMPACT ANALYSIS
Bainbridge Island Municipal Code (BIMC) 15.40 identifies the criteria for when a traffic impact
analysis is required for a development. A traffic impact analysis was not performed for the
development since it was determined that development did not meet the threshold for requiring a
traffic impact analysis. BIMC 15.40.060 states the only exemptions from requiring a traffic impact
analysis are:
“…proposed development or improvement that generates less than 50 average daily trips (ADT)
or five a.m. or five p.m. peak-hour trips per the latest edition of the ITE Trip Generation Manual.”
The trip generation calculations for the 7 single-family residential units, ITE Land Use Code 210, are
summarized in Table 1.
Rolling Sunrise Traffic Impact Review
Gibson Traffic Consultants, Inc. October 2014
info@gibsontraffic.com 2 GTC #14-226
Table 1: Trip Generation Summary
7 New
Single-Family
Residential Units
Average Daily Trips AM Peak-Hour Trips PM Peak-Hour Trips
Inbound Outbound Total Inbound Outbound Total Inbound Outbound Total
Generation Rate 9.52 trips per unit 0.75 trips per unit 1.00 trips per unit
Splits 50% 50% 100% 25% 75% 100% 63% 37% 100%
Trips 34 33 67 1 4 5 4 3 7
It should also be noted that if the ITE regression equation was utilized, based on the recommended
ITE practice, the development would generate 91 average daily trips with 10 PM peak-hour trips.
Table 1 shows that all of the parameters of BIMC 15.40.060 are met, even utilizing the lower trip
generation from the average rate, and therefore a traffic impact analysis for the Rolling Sunrise
development should have been completed. It is important to note that the fact that the development is
proposed to have access to two different roadways does not affect whether or not a traffic impact
analysis is required; the requirement is solely based on the trip generation of the entire development.
The traffic impact analysis could include all, or some, of the following items:
Sight distance at the site entrances
Comparison of surrounding roadways to applicable standards
Impacts to surrounding intersections
Pedestrian and bicycle facilities
Collision history along impacted roadways
Mitigation/improvements to roadways
It is important to note that the analysis, findings and conclusions of the traffic impact analysis,
Revised Code of Washington (RCW) 57.17 and the State Environmental Policy Act (SEPA) provide
a mechanism for the City of Bainbridge Island to require the developer to improve the surrounding
roadway system.
Rolling Sunrise Traffic Impact Review
Gibson Traffic Consultants, Inc. October 2014
info@gibsontraffic.com 3 GTC #14-226
3. ROADWAY ADEQUACY
GTC staff reviewed documentation, including the Hearing Examiner report dated July 18, 2014,
pertaining to the Rolling Sunrise development and conducted field measurements of the roadways
surrounding the Rolling Sunrise development. The Hearing Examiner report and the field
measurements clearly identify that the surrounding roadways are deficient when compared to City of
Bainbridge standards and national standards.
3.1. Hyla Avenue NE
Hyla Avenue NE is currently a dirt/gravel road with between approximately 10 feet and 12 feet of
travel way, based on GTC staff measurements. Along both sides there are trees and vegetation that
establish the limits of the clear travel way. There are approximately 13 existing single-family
residential units along the southern portion of Hyla Avenue NE. Hyla Avenue NE does not have
pedestrian facilities and there are several locations where trees overhanging the roadway limit the
height along the traveled way. This is particularly important when considering the Fire Marshal
requirement, documented in the Hearing Examiner report, that roadways serving the development
shall have 12 feet of drivable width and 13.5 feet of overhead clearance.
3.2. Sunrise Drive NE/NE Duncan Lane
Sunrise Drive NE is paved for the majority of the length and has between approximately 8 feet and
12 feet of traveled way. There are only 11 existing single-family residential units that have access to
Sunrise Drive NE. NE Duncan Lane provides access to only 4 single-family residential units. The
traveled way on both roadways is limited by vegetation and power poles. There are also potential
sight distance issues due to vertical curves along Sunrise Drive NE.
3.3. Roadway Adequacy Findings
The field measurements by GTC staff show that Hyla Avenue NE, Sunrise Drive NE and NE Duncan
Lane are all deficient when compared to City of Bainbridge Island standards and national standards.
The minimum City of Bainbridge Island roadway standards for roadways serving 20 lots or less,
which would be applicable to Hyla Avenue NE and Sunrise Drive NE, require at least a 12-foot
pavement width. Additionally, if a 12-foot pavement width were to serve 2-way traffic, turnouts with
18-feet of pavement width every 300 feet would be required.
The national roadway standards, which would be considered acceptable for vehicular traffic,
pedestrians and safety, are based on the American Association of State Highway and Transportatoin
Officials (AASHTO) A Policy on Geometric Design of Highways and Streets. These AASHTO
standards were utilized when establishing the City of Bainbridge Island roadway standards. The
AASHTO minimum local rural road section based on Table 5-5, which would be most applicable to
Hyla Avenue NE and Sunrise Drive NE, is 18 feet (based on a roadway with a design speed of 15
mph and less than 400 average daily trips). The 18 feet includes 2-foot shoulders on each side of the
roadway. It is important to note that the minimum urban roadway standards include at least 20 feet of
traveled way with separate pedestrian facilities.
Rolling Sunrise Traffic Impact Review
Gibson Traffic Consultants, Inc. October 2014
info@gibsontraffic.com 4 GTC #14-226
The last official posted speed limit approaching Hyla Avenue NE and Sunrise Drive NE is 25 mph.
However, the narrowness of the roadways is likely to reduce the travel speed to below 20 mph. The
minimum stopping sight distance for 25 mph is 150 feet and for 20 mph it is 115 feet. Since the
roadways are both 1-lane roadway, the stopping sight distance should be at least doubled to ensure
two approaching vehicles can stop. (Note: Given the governing equation for stopping sight distance
has one of the velocity parameters squared, doubling these numbers is a simplistic estimation). It is
important to note that these stopping sight distances are not based on a dirt/gravel road and may need
to be increased for Hyla Avenue NE.
The existing Hyla Avenue NE road alignment, specifically the 90-degree horizontal curve at the
proposed access, and encroaching foliage does not appear to provide the sight distance needed for
opposing vehicles to safely stop. Although Sunrise Drive NE does not have a horizontal curve, there
are several vertical curves that could limit the available sight distance. The addition of the Rolling
Sunrise development will increase the likelihood of opposing vehicles meeting on these narrow
roadways. This is especially a concern in areas where there is insufficient sight distance.
4. CONCLUSIONS
The roadways that would provide access to the Rolling Sunrise development, primarily Hyla Avenue
NE and Sunrise Drive NE, do not meet the minimum standards of the City of Bainbridge Island or
AASHTO, including road width, pedestrian facilities and approaching sight distance. Additionally,
they do not meet the requirements for the Fire Marshal for safe access. All of these factors show that
these roadways pose a potential safety hazard for accessing the Rolling Sunrise development,
especially the horizontal curve on Hyla Avenue NE at the development’s proposed access. The access
is likely to have adequate sight distance for vehicle leaving the development. However, there is not
sufficient sight distance through the horizontal curve, the vehicles leaving the Rolling Sunise
development would create a new conflict location and increase the likelihood opposing vehicles
meeting along Hyla Avenue NE.
The Rolling Sunrise development should be required, under RCW 58.17.110 and SEPA, to analyze
the impacts of the development, including roadway deficiencies and safety concerns, in a traffic
impact analysis prior to preliminary plat approval. The traffic impact analysis should identify the
necessary improvements to the surrounding roadways, including safety improvements. The available
right-of-way along Hyla Avenue NE and Sunrise Drive NE is approximately 35 feet, based on
measurements from City of Bainbridge Island Assessor’s data. This available right-of-way is wide
enough to accommodate the City of Bainbridge Island standard roadway width, including the turnout
width, plus pedestrian and drainage facilities.
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