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TECHNICAL MEMORANDUM
Project: Edmonds Shopping Center - Redevelopment Project
Subject: Preliminary Trip Generation Analysis
Date: June 26, 2009
Author: Michelle M. Br -m, Senior Transportation Engineer
Marni C. Heff off; E., Principal Engineer
This memorandum presents the trip generation estimates for the Edmonds Shopping Center
redevelopment project.
1.. Proposed Project
The project proposes to redevelop the existing 5 1, 124 square foot (sf) retail mall located south of the
Edmonds Ferry Terminal. It would demolish the existing mall and construct both commercial (30,302
sf) and residential (up to 360 units) spaces. The project program is summarized in Table 1.
Table 1. Edmonds Shopping Center Proposed Redevelopment
Land Use
Planned Develo meat
Commercial
30,302 sf
Restaurant
10,100 sf
Retail
20,102 sf
Residentlal
286 to 360 units
Condominiums
106 to 144 units
Apartments
180 to 216 units
Parking
423 spaces
Residential
331 spaces
Commercial
92 spaces
Source: UBI Group, June 11, 2009.
2. Trip Generation Methodology
Trip generation for the proposed Edmonds Shopping Center Redevelopment Project was estimated
using rates published by the Institute of Transportation Engineers and a methodology that accounts
for the project's mix of uses and location near major transit facilities. The following briefly defines
the methodology used to determine the trip generation:
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Edmonds Shopping Center Redevelopment Project heffron
Preliminary Pip Generation Analysis . .
I . The total number of "person trips" generated by the proposed uses was determined using
trip generation rates and equations from the Institute of Transportation Engineers (ITE)
Trip Generation, plus information regarding the average number of persons per vehicle.
These person trips reflect all modes of travel to the site including transit, bike, and foot. It
also includes the trips that would be made between on-site uses (internal trips).
2. Internal trips between on-site uses were determined using the methodology in Chapter 7
of the Trip Generation Handbook (ITE, June 2004). Examples of internal trips would
include a resident who makes a morning or evening trip to the retail or restaurant. All of
the internal trips at this site would be expected to be made by foot, so they would not
create vehicle trips.
3. Some of the commute trips are expected to be made by non -automobile modes of travel
(transit, train, bicycle or walking). For this site vicinity, Puget Sound Regional Council
(PSRC) provided data showing non -automobile rates of 10% based on year 2000 Census
surveys. This rate was used; however, it is expected the non -automobile rate would be
higher for the proposed residences since they would have direct access to the Sound
Transit Commuter Rail Station, which was not yet built when the latest Census was
performed. The remaining 90% of the trips were assumed to be made by single -occupant
vehicles or carpools. Mode of travel assumptions are detailed in Section 4 below.
4. The commercial trips (retail and restaurant) were divided into three trip types—pass-by
trips, diverted -linked trips, and primary trips—using information from the Trip
Generation Handbook. Further information related to various trip types is described in
Section 4 below.
All of the assumptions listed above were used to determine the number of trips that would be
generated by buildout of the site. Key information from these calculations includes vehicle trips,
transit trips, and pedestrian/bicycle trips. This same retail mode splits and trip types were used to
calculate the existing trip generation for the site. Although internal trips are likely to occur within the
existing retail mall, no reductions were assumed since the retail space is assumed as one entity. The
difference between the existing and proposed trip generation results in the net increase in traffic due
to the proposed project.
Rates and equations found in Trip Generation (Institute of Transportation Engineers [ITE], 8th
Edition, 2008) were used. For the existing and proposed retail uses, "Shopping Center" (Land Use
Code 820) rates were used. "High -Turnover Restaurant" (Land Use Code 932) rates were used for the
proposed restaurant. "Apartment" (Land Use Code 220) rates were used for all the proposed multi-
family residential units, which have a slightly higher rate than "Condominium/Townhouse" (Land
Use Code 230) to account for a worst-case condition.
3. Summary of Trip Generation Results
Table 2 presents the net increase in vehicle trips associated with redevelopment of the site. Some of
the retail trips come from traffic already using roadways adjacent to the site, and some may divert
from roadways further away. Table 3 summarizes the estimated number of pass -by, diverted, and
primary trips for the project. The proposed redevelopment is expected to generate about 3,660 vehicle
trips per day and about 332 vehicle trips during the PM peak hour. Of the PM peak hour trips, 238
would be primary trips that are new to the site area. Further information related to the assumed trip
types are presented later in Section 4 below.
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Edmonds Shopping Center Redevelopment Project
Preliminary Trip Generation Analysis
Table 2. Proposed Vehicle Trips — by Land Use
•
trans ortation inc.
Source: Heffron Transportation, Inc. June 25, 2009.
Table 3. Proposed Vehicle Trips - by Trip Type
Trip Type
Daily Vehicle
Tris
Daily
Vehicle
AM Peak Hour Vehicle Tris
PM Peak Hour Vehicle Trips
In
Out
Total
In
Out
Total
Land Use
Size
Tris
Retail
20,202 sf
710
10
6
16
30
31
61
Restaurant
10,100 sf
1,030
49
45
94
54
37
91
Residential
360 units
1,920
25
125
150
120
60
180
Total
+214
3,660
84
176
260
204
128
332
Source: Heffron Transportation, Inc. June 25, 2009.
Table 3. Proposed Vehicle Trips - by Trip Type
Trip Type
Daily Vehicle
Tris
AM Peak Hour Vehicle Trips
PM Peak Hour Vehicle Trips
In Out Total
In Out Total
Primary Trips
Diverted -Linked Trips
Pass -by Trips
2,580
390
690
49
12
23
84
141
12
23
176
190
24
46
260
157
17
30
204
81
17
30
128
238
34
60
332
Total
3,660
Source: Heffron Transportation, Inc. June 25, 2009.
Table 4 shows the existing trip generation by trip type. The difference between the two developments is
the net increase in trips related to the proposed redevelopment. The redeveloped site would increase the
vehicle trips at the site driveways by 1,680 daily trips, 214 AM peak hour, and 160 PM peak hour trips.
Table 4. Vehicle Trips by Trip Type — Existing Retail Mall
Source: Heffron Transportation, Inc. June 25, 2009.
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June 26, 2009
Daily
Vehicle
AM Peak Hour Vehicle Trips
PM Peak Hour Vehicle Trips
In
Out
Total
In
Out
Total
Trip Type
Tris
Primary Trips
790
14
4
18
32
36
68
Diverted -linked Trips
510
6
6
12
23
23
46
Pass -by Trips
680
8
28
8
18
16
46
29
84
29
88
58
172
Total
1,980
Net Change to Proposed
+11,680
+56
+158
+214
1 +120
+40
+160
Source: Heffron Transportation, Inc. June 25, 2009.
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June 26, 2009
Edmonds Shopping Center Redevelopment Project he f f r on
Preliminary Trip Generation Analysis • • •
4. Detailed Trip Generation Assumptions and Calculations
This section presents detailed information related to the assumptions and methodology used to determine
the site's trip generation. It defines and explains how the number of person trips was calculated, and then
describes the modes of travel for those trips including vehicle trips, transit trips and pedestrian/bicycle
trips (non -vehicle trips). The following subsections detail the trip rates used in the analysis, internal trips
expected to be made between uses on the site, mode of travel, and retail trip characteristics.
Person Trips
Trip generation for new projects is typically determined using rates and equations in Trip Generation
(Institute of Transportation Engineers [ITE], 8th Edition, 2008). This reference manual summarizes the
results of numerous traffic studies throughout the country for a variety of land -use types. The applicable
rates and equations in ITE's Trip Generation are based on studies of stand-alone suburban land uses. As
a result, trip generation rates for residential and retail uses reflect the suburban trend of driving in
single -occupant vehicles (SOVs). However, the Edmonds Shopping Center site is not an isolated
suburban site—it is located near downtown Edmonds with some residents who live within walking
distance of the site. It is also located within walking distance of the Edmonds Ferry Terminal, and the
Sound Transit Commuter Rail Station. As recommended by ITE in Trip Generation, the ITE trip
generation rates were adjusted to account for these other travel modes.
The ITE trip generation rates and equations were used as the basis for determining the number of per-
son trips for all uses. Person trips are the total number of trips made by all modes of travel, including
carpooling, transit, walking and bicycling. The person trips were determined by applying an average
vehicle occupancy (AVO) factor to the ITE vehicle trips for each land use. The assumed AVO factors
and mode of travel percentages for each land use are summarized in Table S.
Table 5. Mode Split and Average Vehicle Occupancy (AVO)
Assumption
Residential
Land Use
Retail
Restaurant
Assumed AVO Rate Applied to ITE Rates
1.09 a
1.20 b
1.52c
AVO Rate for Site Area in Edmonds
1.09 a
1.20 b
1.52
Non -vehicle Trips d
10%
10%
10%
Person Trips by Vehicle
90%
90%
90%
Source: Heffron Transportation, Inc., June 1, 2009.
a. Estimated AVO rate (personsA eftle) since none are fisted for residential uses, based on 'Journey to Work' Census 2000 data for
Transportation Anis Zone (TAZ) 578, whfch encompasses the site.
b. AVO rates are not published for these uses; estimated by Heffron Transportation and assumed to remain unchanged in site area
c. AVO rate Imm ITE's Trip Generation for Restaurant assumed the same as AVO rate in Edmonds.
d. Non -vehicle trips (transit, train, walking/bicycling) based on Joumeydo-Work surveys for residential uses.
heffron - 4 - June 26, 2009
Edmonds Shopping Center Redevelopment Project h e f f r o n
Preliminary Trip Generation Analysis
Internal Trips
The total number of trips generated by a mixed-use site includes "internal trips," or trips made
between one use on the site and another use on the site. For example, a trip that a resident makes to
the retail space is included in the trip generation values for both the residential unit and the retail
space. All of the internal trips at this site are expected to be made by foot, and would not create
vehicle trips.
Chapter 7 of the Trip Generation Handbook is devoted to estimating trip generation for multi -use
developments, and includes a methodology to estimate the number of internal trips that can be
expected at specific types of sites. This method is based on the type and size of various land uses. The
more balanced the mix of uses, the higher the percentage of internal trips. Developments with a
predominance of one type of use (e.g., mostly retail or mostly residential) typically have a lower
percentage of internal trips.
ITE's methodology to determine internal trips includes several steps:
1. Determine the number of trips expected to be generated by each land use as if each was
on a separate site.
2. Determine the number of internal trips based on internal capture rates presented in the
Trip Generation Handbook.
3. Balance the number of internal trips to and from all land uses at the site.
4. Total the resulting number of internal trips and calculate the percentage of internal trips.
Using the methodology described above, the internal capture rates for the various alternatives were
estimated and are shown in Table 6.
Table 6. Intemal Capture Summary — Trips between Proposed Site Uses
% of Internal Trips for Each Land Use
Land Use Daily AM Peak Hour PM Peak Hour
Retail 10% 10% 10%
Restaurant 10% 10% 10%
Residential 11% 10% 11%
Source: Heffron Transportation, Inc., June 25, 2009. Rates were derived from methodology in the Trig
Generation Handbook (ITE, June 2004).
Mode of Travel
The site is located adjacent to Sound Transit's Edmonds Commuter Rail Station and Washington
State Ferry Terminal. It is also located within walking distance to downtown Edmonds and the
residential population there. Because of its location, some of the trips are expected to be made by
non -automobile modes of travel (transit, train, bicycle, or walking). For this site vicinity, Puget Sound
Regional Council (PSRC) provided data showing non -automobile rates of 10% based on year 2000
Census surveys. It is expected that this rate is conservatively low given that it is almost a decade old
(newer data are not available), and were taken before the Sound Transit station was built. The
remaining 90% of the trips were assumed to be made by single -occupant vehicles or carpools. The
mode -of -travel assumptions for each land use were previously presented in Table 5.
heffron - 5 - June 26, 2009
Edmonds Shopping Center Redevelopment Project
Preliminary Trip Generation Analysis
Retail Trip Characteristics
trans ortation, inc.
Retail trips are different than other types of trips that the site would generate. Unlike residential trips,
retail developments attract a portion of their trips from traffic that is already using streets in the site
vicinity. Retail trips are typically divided into three trip types—pass-by trips, diverted -linked trips,
and primary trips—which are described further below.
• Pass -by trips are trips that are already on a roadway immediately adjacent to the site en route
to another destination. For example, people driving along Sunset Avenue S could stop and
shop or dine at the site. This would be a pass -by trip. Pass -by trips do not require a diversion
from another roadway.
• Diverted -linked trips are trips that are attracted from the traffic on roadways within the
vicinity of the site, but that require a diversion from that roadway to another roadway to gain
access to the site. For this site, a diverted -linked trip could be one that comes from Main
Street. These trips would divert to local roadways to access the site.
New (primary) trips are single -purpose trips generated by retail or a restaurant. New trips
are generally assumed to begin and end at home, although some new trips could originate at
work or other locations.
The percentage of driveway trips that is attributed to each of the above components depends on the size,
type, and location of a proposed project. Information in the Trip Generation Handbook was used to
derive the percentages for this site. The trip type assumptions are presented in Table 7.
Table 7. Assumed Trip Characteristics
% of Trips for Each Land Use
Land Use Primary Tris Pass -by Tris Diverted -Linked Trips
Retail 40% 34% 26°%
Restaurant 37% 43°% 20°%
Residential 100°% 0% 0%
Source. Heffron Transpodation, Inc., June 25, 2009. Rates were derived from information in the Trig
Generation Handbook (ITE, June 2004).
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heffron - 6 - June 26. 2009