Driveway Access Safety Assessment Update recd 10-29-15.pdfWilliam Popp Associates
October 28, 2015
To:
C/o:
From:
Subject:
Re:
Phong Le
Clear Vision Homes, Inc.
Renton, WA
Terrance Randall Wilson
Managing Partner Attorney at Law
Wilson & Neal, PLLC
William Popp Jr.
Senior Transportation Engineer
William Popp Associates
Edmonds Short Plat: 18227 801h Ave W
Three Single -Family Residential Lots
City of Edmonds, WA
Transportation Engineers/Planners
(425) 401-1030
FAX (425) 401-2125
e-mail: info@wmpoppassoc.com
OCT 19 1015
DEVELOPMENT SERVICES
DRIVEWAY ACCESS SAFETY ASSESSEMENT UPDATE
The following report was prepared to identify the driveway access operations and safety
for a proposed short plat located in the northeast vicinity of the City of Edmonds. The
plat is located at 18227 80th Ave W, TPN 00370800101400. The proposed layout
includes dividing one lot into three, with the existing house to remain. The two new lots
would be on the east side of the parcel east of the existing home. This layout is shown in
Attachment 1. This report is an update to a previously submitted report dated May 8,
2014.
The current proposed short plat design includes three separate driveway stems that come
together in a 20' x 30' easement on the northwest corner of the property with access to
80th Ave W, see Attachment la. With this short plat concept, each of the three lots
exceeds the City's 12,000 sf minimum threshold. The lot areas of each lot are: Lot 1 at
12,408 sf, Lot 2 at 12,480 sf, and Lot 3 at 12,303 sf.
14-400 Building . Suite 206. 14400 Be] -Red Road . Bellevue, WA 98007
Driveway Access Assessment Study (10/28/15) 18227 &YAve W
Roadway Inventory
801h Ave W in the vicinity of the site is a two-lane two-way street with 10 to 11' lanes,
and variable width paved shoulders (nominal widths). Traffic control consists of side -
street stop signs on abutting local streets. There is an all -way stop at 186`" St SW (four-
way) and a step sign at Olympic View Drive where 80"h Ave W turas into 180th St SW.
A survey of 801h Ave W was conducted by Lanktree Land Surveying, Inc. in April 2014.
A detailed review of the survey and sight distance is discussed later.
The posted speed limit on 801h Ave W is 25 mph. The pavement is in excellent condition
(per WADT_PSC; 96 to 100 score). It is important to note that there is a steep grade
(+15% northbound) between 184"' St SW and just south of the subject property,
approximately 250 feet in length. There is a vertical curve near the site, and north of the
site the roadway grade is -5% northbound. There are no horizontal curves on 80th Ave W,
except at the north end where the roadway turns east and becomes 180"h St SW.
According to the City's 2009 Comprehensive Plan, this roadway is currently identified as
a "local street" (per Figure 3-2; Existing Federal Functional Classifications) but is
recommended as a "Collector" between 2001h and Olympic View Dr (per Figure 3-3;
Recommended Road Functional Classifications). The City's definition of a Collector
includes, among other criteria, traffic volumes that range between 1,000 and 5,000 ADT.
The most recent count on 80'h Ave W is 2,1001 ADT, thus the route would pass that
measure of a "Collector".
801h Ave W is not a designated bikeway nor is it in the long range plan. In addition there
are no sidewalk amenities and there are no current designated paved walkways along it.
However, it should be noted that a long range planned sidewalk improvement (5'
sidewalk with curb and gutter west side only, 3000 feet) is identified in the Comp Plan
for this roadway (Pedestrian project L6).
There are no traffic calming devices on 801h Ave W in the project vicinity, and none are
planned. It should be noted also that per City guidelines traffic calming features in
general are only permitted on local streets.
Selected photos both northbound and southbound along 801h Ave W are shown in
Attachment 2.
Nearby Residential Driveways
The adjacent parcels to the north and to the south (east side of 801h Ave W) both are
occupied with single-family homes and their direct driveway accesses to 80th Ave W are
William Popp Associates Page 2
Driveway Access Assessment Stud), (10/28/15) 18227 80`h Ave W
approximately 1' and 14' from their nearby driveway edge to their respective abutting
property lines. The abutting south lot also has a gravel parking area that is about 1' from
the property line.
There are three lots occupied with single-family homes on the west side of 801h Ave W in
the vicinity of this site and each has single driveway access directly to 80`h Ave W.
Site Trip Generation
There are only three lots as part of this short plat, Lot 1 includes an existing home that
will remain. Thus simply stated, there will be 3 trips maximum during peak hour periods,
For daily traffic volume projections, there would be a maximum of 30 ADT (average
daily trips).
Sight Distance
There are two sight distance parameters generally applicable to site development. One is
intersection (or entering) sight distance (ISD/ESD) from project driveways and the other
is stopping sight distance (SSD).
Intersection sight distance requirements are the design parameters set forth in order to
provide sufficient sight distance for entering vehicles such that they do not impede the
mainline traffic speed and in -turn do not reduce the capacity of the roadway. In general, it
is understood that intersection sight distance relates more to driver comfort and roadway
capacity rather than safety. It should be noted that Snohomish County EDDS notes that
ISD shall not apply for non -arterial intersections where the minor road or access is 80
ADT or less.
In this specific case, 801h Ave W is a non -arterial and the driveway ADT is less than 80.
Therefore, for low volume driveways accessing low volume streets, available sight
distance at the project site access points is typically based solely on stopping sight
distance requirements per AASHTO. In general, the available stopping sight distance on
a roadway should be sufficiently long to enable a vehicle traveling at or near the design
speed to stop before reaching a stationary object in its path. In this particular case the
stopping sight distance is measured based on the sight line between the entering vehicle's
motorist eye height from the driveway setback 14.5 feet from edge of traveled way and
the approaching vehicle's motorists eye height; both eye heights are assumed to be 3.5
feet above ground.
The minimum acceptable values for safe stopping sight distance were obtained from the
AASHTO A Policy on Geometric Design of Highways and Streets 2004, Exhibit 3-1 and
adjusted for grade based on AASHTO Equation 3-3: d=V2/[30((a/32.2) ± G)]
William Popp Associates Page 3
Driveway Access Assessment Study (10/28/15) 18227 801" Ave W
In general the minimum SSD is 155 feet at 25 mph for a roadway grade between -3% and
+3%.
The sight distance conditions for left and right exiting viewing scenarios at the proposed
driveway (Sta 13+64 +/-) was surveyed given the AASHTO parameters of a driveway
vehicle eye height of 3.5 feet above grade and 14.5 feet set back from edge of traveled
way (fog line in this case) to the center of the lane for the approaching vehicle, with a
reciprocal eye height of 3.5 feet. The sight lines that were reviewed are shown in plan
view in Attachment 3. The roadway profile of 801h Ave W through the project vicinity is
shown in Attachment 4. In Attachment 4, point A is the centerline of 80th Ave W at the
center of the subject plat's north driveway location.
The two sight line scenarios reviewed are discussed and summarized below:
a. Looking North (sight line A'B).
A' is the location at the north driveway 14.5 feet back from fog line of 801h Ave W.
The point B is the middle of the southbound lane 250 feet from the north driveway.
The sight line looking north from the north driveway was measured to be more than
adequate. The sight line was measured up to 250 feet without obstruction, and likely
further but not measured. Based on the grade of +5% southbound and a posted speed
of 25 mph the minimum required SSD is 144 feet. At 35 mph with same grade, the
minimum required SSD is 231 feet.
b. Looking South (sight line A'C)
Again, A' is the location on the north driveway 14.5 feet back from fog line of 80th
Ave W. Point C is the middle of the northbound lane where an approaching vehicle
is first visible. The sight line looking south from the north driveway was measured
to be 215 feet. The grade of 801h Ave W approaching the vertical curve in the
northbound direction is +15%. However, the grade from when the approach vehicle
is first seen by the driveway motorist to the site access is -0.4% or essentially 0%
since it falls within the +3% condition. Based on this, the minimum required SSD
for 25 mph is 155 feet, thus it is concluded the available SSD of 215 feet is adequate.
The available SSD accommodates a maximum speed condition of just over 31 mph.
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Driveway Access Assessment Study (10/28/15) 18227 801" Ave W
Accident History
According to the City's 2009 Comprehensive Plan, 801h Ave W is not identified as a high
accident corridor.
Findings and Conclusions
Based on the foregoing analysis for the proposed 18227 801h Ave W short plat, the
following traffic findings and conclusions are presented:
The average weekday volume on 801h Ave W is approximately 2,100 vpd which
typically suggests a PM peak hour volume of approximately 210 vph. Since the
driveway volume would only be about 3 vehicles during peak hour conditions, the
intersection level of service for the driveways is clearly LOS A. A formal level of
service analysis was not conducted given the low volumes.
The available sight distance at the proposed north easement access for all three lots
for vehicles exiting (left and right turn out) was calculated to exceed the minimum
safe stopping sight distance requirements of 155 feet per 2004 AASHTO for 25 mph
posted speed limit. The measured sight line exceeds 250 feet looking north and is
approximately 215 feet looking south.
The sight lines as surveyed from the proposed driveway setbacks were presumed free
of sight line obstructions, including parked vehicles and vegetation.
The existing 801h Ave W length of vertical curve as measured from centerline profile
is approximately 135 feet, and the algebraic difference in intersecting grades is 12
(A=15%-3%). According to AASHTO design criteria for vertical curves, the rate of
vertical curvature is 11.2 (K) which per AASHTO Exhibit 3-72 corresponds to a
design speed of 25 mph and a minimum safe stopping sight distance of 155 feet. The
SSD as measured from the profile is approximately 120 feet for a 3.5 eye height and
2' object height. This would suggest the actual design speed applicable for measured
SSD is between 20 and 25 mph and likely closer to 20 mph.
According to the 2009 Comprehensive Plan, 80th Ave W is not identified as a high
accident corridor.
The proposed shared access driveway for the three lots is a very low volume condition
and thus conflicts between entering and exiting movements and the adjacent north
driveway as well as the opposite side of street driveway would be extremely
infrequent.
William Popp Associates Page 5
Driveway Access Assessment Study (10/28/15) 18227 801" Ave W
• There are existing warning signs stating "Limited Sight Distance" W14-4 (24" x 24")
approximately 250 feet in advance of the vertical curve in both directions. This type
of sign is no longer recognized in the 2009 MUTCD.
Recommendations
The mitigation recommendations for the 18227 801h Ave W three -lot short plat are as
follows:
The shared access (for all three of the lots) at the northwest corner of the site should
be located at least 8 feet south from the neighboring driveway to the north. The 8 foot
driveway spacing distance is measured from edge of driveway to edge of driveway.
The current paving plan in Attachment la shows 8 feet separation between these two
driveways.
2. Given the new MUTCD conditions, it is recommended that the existing warning signs
stating "Limited Sight Distance" W14-4 (24x24) located approximately 250 feet in
advance of the vertical curve in both directions be removed. Alternatively, they could
remain as a grand -fathered condition to be used as advance warning of limited sight
distance for the approaching the vertical curve, to be augmented with
Recommendation #3.
3. Applicable to this specific vertical curve situation, it is recommended that a new sign
the "Hill Blocks View" W7-6 (24x24) be placed in advance of the vertical curve in
both directions. In addition, it is recommended that an Advisory Speed W13 -1P
(18x18) sign indicating a speed of 20 mph be installed as a supplemental sign below
the new W7-6. The location of these signs shall be per MUTCD Table 2C-4 -- given
a posted speed of 25 mph and an advisory speed of 20 mph, the MUTCD stats that
"No suggested distances are provided for these speeds, as the placement location is
dependent on site conditions and other signing. An alignment warning sign may be
placed anywhere from the point of curvature up to 100 feet in advance of the curve.
However, the alignment warning sign should be installed in advance of the curve and
at least 100 feet from any other signs." Any other signs are presumed to only be
warning or regulatory type signs on 801h Ave W.
ATTACHMENTS:
1. Short Plat Parcel Map
1 a. Access Easement Paving Plan
2. Roadway pictures
3. Site and 80"' Ave W Plan View Surveyed Sight Lines for Profiles
4. 80th Ave W Roadway Centerline Profile through project vicinity
5. Sight Distance Profile North Driveway Location
William Popp Associates Page 6
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PAVING PLAN
Access Easement Area Detail
(per Sheet 2.1 of TEC civil plan set)
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FRONTAGE IMPROVEMENTS
LOT 1 SS STUB
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Attachment 1 a
aubtting southside parcel (east side of 80th Ave W)
LOOKING SOUTH (vicinity of site)
LOOKING SOUTH (north of 182nd St SW)
80th Ave W
Nortbhound and Southbound Pictures
LOOKING NORTH (near top of grade)
LOOKING NORTH (begin of grade)
LOOKING NORTH south of 184th St SW)
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