08-102166Cramer Northwest, Inc.
1'4 Surveyors *Planners •Engineers— f D2� �Q`C
April 25, 2008
City of Federal Way
Public Works Department
Cary Roe, Director of Public Works
33325 8'h Ave S
Federal Way WA 98063
RE: Right of Way Modification Request
1846 S 296 h Street, Cantu Short Plat
Mr. Roe,
We are m the preliminary planning stages of the Cantu Short Plat. Thee site is approximately three-quarters of an
acre and currently has a single family home located on the site. The proposal is for 3 additional single family lots,
bringing the total to 4 with the existing residence. The site is currently being served by two paved roadways, S 296`h
Street and 19'h Ave S both of which are categorized as local streets according to the City of Federal Way Street Map.
The site also fronts 2& Ave S, which is an unimproved road. The current house served by two driveways off of S
296'h Street.
Upon finiher discussion with City consultants, a sight distance review was requested for S 296h Street. S 296h
Street slopes east to west, west at 19,' Ave S being the low side. The S 296 Street hill crests at 2& Ave S, the
concern from staff is that the visibility entering and existing out onto S 29e Street would be obstructed by the hill.
The AASHTO standard for stopping distance is 250' on a street posted at 25 mph, entering for a right tam is 335'
and for a left turn it is 390' (see attached chart). As you can tell from the profile (2007-175SD 1), at our current
proposed joint access driveway we did not have the proper stopping distance for either turn. To see clearly, Our
stopping distance was 213' to the east and 226' to the west.
We are asking to continue to use the existing driveway to continue to serve the existing home. It is attested to by the
current owner that he doesn't believe there have been any accidents using the driveway where it is currently located.
Further, we are requesting to serve two new single family homes to the east with a joint use driveway at the location
shown on the plans and measured as discussed above. We believe that since S 296th Street is the more improved
street, and will be further improved with this subdivision, and will be the better road to serve the new lots. We are
prepared to take direction from staff with regards to any safety measures that might be necessary.
Thank you for your consideration.
Sincerel ,
Akkma Kondeiis
Project Manager
Enclosures
RECEIVED
MAY 0 2008
Cc: Will Appleton CITY OF FEDERAL WAY
CDS
945 N. Central, Suite #104 Kent WA 98032 (253) 852-4880 Fax (253) 852-4955
-unuty rrnmPrnxv rnm F-mail• rni(n1,rrnmPm1Ar rnm
AASHTO-Geometric Design of Highways and Streets
Time gap (tg) (seconds) at design
Design vehicle seed of major road
Passenger car 6.5
Single -unit truck 8.5
Combination truck 10.5
Note: Time gaps are for a stopped vehicle to turn right onto or cross a
two-lane highway with no median and grades 3 percent or less.
The table values require adjustment as follows:
For multilane highways:
For crossing a major road with more than two lanes, add
0.5 seconds for passenger cars and 0.7 seconds for trucks
for each additional lane to be crossed and for narrow
medians that cannot store the design vehicle.
For minor road approach grades:
If the approach grade is an upgrade that exceeds
3 percent, add 0.1 seconds for each percent grade.
Exhibit 9-57. Time Gap for Case 112-Right Turn from Stop
and Case B3-Crossing Maneuver
Metric
US Customary
Intersection sight
Intersection
sight
Stopping
distance
for
Stopping
distance
for
Design
sight
passenger
cars
Design
sight
passenger
cars
speed
distance
Calculated
Design
speed
distance
Calculated
Design
(kmJh)
(m)
m
m
(mph)
(ft}
ft
ft
20
20
36.1
40
15
80
143.3
145
30
35
54.2
55
20
115
191.1
195
40
50
72.3
75
25
155
238.9
240
50
65
90.4
95
30
200
286.7
290
60
85
108.4
110
35
250
334.4
335
70
105
126.5
130
40
305
382.2
385
80
130
144.6
145
45
360
430.0
430
90
160
162.6
165
50
425
477.8
480
100
185
180.7
185
55
495
525.5
530
110
220
198.8
200
60
570
573.3
575
120
250
216.8
220
65
645
621.1
625
130
285
234.9
235
70
730
668.9
670
75
820
716.6
720
80
910
764.4
765
Note: Intersection sight distance shown is for a stopped passenger car to turn right onto or cross a
two-lane highway with no median and grades 3 percent or less. For other conditions, the time
gap must be adjusted and required sight distance recalculated
Exhibit 9-58. Design Intersection Sight Distance -Case 132-Right Turn from Stop and
Case 113-Crossing Maneuver
Intersections
Metric
US Customa
IntersecI
Intersection sight
Stopping
distan
Stopping
distance for
Design
sight
assenpassengerDesign
sight
assen
er cars
speed
distance
Calculatespeed
distance
Calculated
Design
(km/h)
(m)
m(mph)
(ft)
ft
ft
20
20
41.7
45
15
80
165.4
170
30
35
62.6
65
20
115
220.5
225
40
50
83.4
85
25
155
2.-6_0
280
50
65
104.3
105
.30
200
330.8
335
60
85
125.1
130
35
250
385.9
390
70
105
146.0
150
40
305
441.0
44�5
80
130
166.8
170
45
360
496.1
a00)
90
160
187.7
190
50
425
551.3
555
100
185
208.5
210
55
495
606.4
610
110
220
229.4
230
60
570
661.5
665
120
250
250.2
255
65
645
716.6
720
130
285
271.1
275
70
730
771.8
775
75
820
826.9
830
80
910
882.0
885
Note: Intersection sight distance shown is for a stopped passenger car to turn left onto a
two-lane highway with no median and grades 3 percent or less. For other conditions, —
the time gap must be adjusted and required sight distance recalculated...
Exhibit 9-55. Design Intersection Sight Distance —Case B1—Left Turn from Stop
Sight distance design for left turns at divided -highway intersections should consider multiple
design vehicles and median width. If the design vehicle used to determine sight distance for a
divided -highway intersection is larger than a passenger car, then sight distance for left turns will
need to be checked for that selected design vehicle and for smaller design vehicles as well. If the
divided -highway median is wide enough to store the design vehicle with a clearance to the
through lanes of approximately 1 m [3 ft] at both ends of the vehicle, no separate analysis for the
departure sight triangle for left turns is needed on the minor -road approach for the near roadway
to the left. In most cases, the departure sight triangle for right turns (Case 132) will provide
sufficient sight distance for a passenger car to cross the near roadway to reach the median.
Possible exceptions are addressed in the discussion of Case B3.
If the design vehicle can be stored in the median with adequate clearance to the through
lanes, a departure sight triangle to the right for left turns should be provided for that design
vehicle turning left from the median roadway. Where the median is not wide enough to store the
design vehicle, a departure sight triangle should be provided for that design vehicle to turn left
from the minor -road approach.
The median width should be considered in determining the number of lanes to be crossed.
The median width should be converted to equivalent lanes. For example, a 7.2-m [24-ft] median
should be considered as two additional lanes to be crossed in applying the multilane highway
adjustment for time gaps in Exhibit 9-54. Furthermore, a departure sight triangle for left turns
661
Intersections
Metric
US Customa
Intersection sight
Intersection
sight
distance
distance
Design
Stopping
Passen er cars
Design
Stopping
Passenger
cars
speed
sight
Calculated
Design
speed
sight
Calculated
Design
(km/h)
distance (m)
m
m
(mph)
distance (ft)
ft
ft
20
20
30.6
35
15
80
121.3
125
30
35
45.9
50
20
115
161.7
165
40
50
61.2
65
25
155
202.1
205
50
65
76.5
80
30
200
242.6
245
60
85
91.7
95
35
250
283.0
285
70
105
107.0
110
305
323.4
325
80
130
122.3
125
360
363.8
365
90
160
137.6
140
50
425
404.3
405
100
185
152.9
155
55
495
444.7
445
110
220
168.2
170
60
570
485.1
490
120
250
183.5
185
65
645
525.5
530
130
285
198.8
200
70
730
566.0
570
75
820
606.4
610
80
910
646.8
650
Note: Intersection sight distance shown is for a passenger car making a left turn from an
undivided highway. For other conditions and design vehicles, the time gap should be
adjusted and the sight distance recalculated.
Exhibit 9-67. Intersection Sight Distance —Case F—Left Turn from Major Road
If stopping sight distance has been provided continuously along the major road and if sight
distance for Case B (stop control) or Case C (yield control) has been provided for each minor -
road approach, sight distance will generally be adequate for left turns from the major road.
Therefore, no separate check of sight distance for Case F may be needed.
However, at three -leg intersections or driveways located on or near a horizontal curve or
crest vertical curve on the major road, the availability of adequate sight distance for left turns
from the major road should be checked. In addition, the availability of sight distance for left turns
from divided highways should be checked because of the possibility of sight obstructions in the
median.
At four -leg intersections on divided highways, opposing vehicles turning left can block a
driver's view of oncoming traffic. Exhibit 9-98, presented later in this chapter, illustrates
intersection designs that can be used to offset the opposing left -turn lanes and provide left -turning
drivers with a better view of oncoming traffic.
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Metric
US Customary
Design
Stopping
sight
distance m
Design
Stopping
sight
distance ft
speed
(mph)
Downgrades
3% 6% 9%
Upgrades
3% 6% 9%
speed Downgrades Up2rades
(km/h) 3% 6% 9% 3% 6% 9%
20
20
20
20
19
18
18
15
80
82
85
75
74
73
30
32
35
35
31
30
29
20
116
120
126
109
107
104
40
50
50
53
45
44
43
25
158
165
173
147143
_140
50
66
70
74
61
59
58
30
205
215
227
200
184
179
60
87
92
97
80
77
75
35
257
271
287
237
229
222
70
110
116
124
100
97
93
40
315
333
354
289
278
269
80
136
144
154
123
118
114
45 37-''400
427
331
320
90
164
174
187
148
141
136
50
474
507
405�
388
375
100
194
207
223
174
167
160
55
520
553
593
469
450
433
110
227
243
262
203
194
186
60
598
638
686
538
515
495
120
263
281
304
234
223
214
65
682
728
785
612
584
561
130
302
323
350
267
254
243
70
771
825
891
690
658
631
75
866
927
1003
772
736
704
80
965
1035
1121
859
817
782
Exhibit 3-2. Stopping Sight Distance on Grades
Decision Sight Distance
Stopping sight distances are usually sufficient to allow reasonably competent and alert
drivers to come to a hurried stop under ordinary circumstances. However, these distances are
often inadequate when drivers must make complex or instantaneous decisions, when information
is difficult to perceive, or when unexpected or unusual maneuvers are required. Limiting sight
distances to those needed for stopping may preclude drivers from performing evasive maneuvers,
which often involve less risk and are otherwise preferable to stopping. Even with an appropriate
complement of standard traffic control devices in accordance with the MUTCD (6), stopping
sight distances may not provide sufficient visibility distances for drivers to corroborate advance
warning and to perform the appropriate maneuvers. It is evident that there arc many locations
where it would be prudent to provide longer sight distances. In these circumstances, decision
sight distance provides the greater visibility distance that drivers need.
Decision sight distance is the distance needed for a driver to detect an unexpected or
otherwise difficult -to -perceive information source or condition in a roadway environment that
may be visually cluttered, recognize the condition or its potential threat, select an appropriate
speed and path, and initiate and complete the maneuver safely and efficiently (7). Because
decision sight distance offers drivers additional margin for error and affords them sufficient
length to maneuver their vehicles at the same or reduced speed, rather than to just stop, its values
are substantially greater than stopping sight distance.
Drivers need decision sight distances whenever there is a likelihood for error in either
information reception, decision making, or control actions (8). Examples of critical locations
where these kinds of errors are likely to occur, and where it is desirable to provide decision sight
distance include interchange and intersection locations where unusual or unexpected maneuvers
are required, changes in cross section such as toll plazas and lane drops, and areas of concentrated
115
Elements of Design
Criteria for Measuring Sight Distance
Sight distance is the distance along a roadway throughout wluch an object of specified
height is continuously visible to the driver. This distance is dependent on the height of the
driver's eye above the road surface, the specified object height above the road surface, and the
height and lateral position of sight obstructions within the driver's line of sight.
Height of Driver's Eye
For sight distance calculations for passenger vehicles, the height of the driver's eye is
considered to be 1 080 mm [3.5 ft] above the road surface. This value is based on a study (4)
found that average vehicle heights have decreased to 1 300 mm [4.25 ft] with a comparable
decrease in average eye heights to 1 080 mm [3.5 ft]. Because of various factors that appear to
place practical limits on further decreases in passenger car heights and the relatively small
increases in the lengths of vertical curves that would result from further changes that do occur,
1 090 mm [3.5 ft] is considered to be the appropriate height of driver's eye for measuring both
stopping and passing sight distances. For large trucks, the driver eye height ranges from 1 800 to
2 400 mm [5.9 to 7.9 ft]. The recommended value of truck driver eye height for design is
2 330 mm [7.6 ft] above the roadway surface.
Height of Object
For stopping sight distance calculations, the height of object is considered to be 600 mm
[2,0 ft] above the road surface. For passing sight distance calculations, the height of object is
considered to be 1 080 thin [3.5 ft] above the road surface.
Stopping sight distance object. The basis for selection of a 600-mill [2.0-ft] object height
was largely an arbitrary rationalization of the size of object that might potentially be encountered
in the road and of a driver's ability to perceive and react to such situations. It is considered that an
object 600 mm [2.0 ft] high is representative of an object that involves risk to drivers and can be
recognized by a driver in time to stop before reaching it_ Using object heights of Less than
600 mm [2.0 ft] for stopping sight distance calculations would result in longer crest vertical
curves without documented safety benefits (4). Object height of less than 600 mm [2.0 ft] could
substantially increase construction costs because additional excavation would be needed to
provide the longer crest vertical curves. It is also doubtful that the driver's ability to perceive
situations involving risk of collisions would be increased because recommended stopping sight
distances for high-speed design are beyond most drivers' capabilities to detect small objects (4).
Passing sight distance object. An abject height of 1 0g0 mm (3.5 ft] is adopted for passing
sight distance. This object height is based on a vehicle height of 1 330 mm [4.35 ft], which
represents the 15th percentile of vehicle heights in the current passenger car population, less an
allowance of 250 min 10.92 ft), which represents a near -maximum value for the portion of the
vehicle height that needs to be visible for another driver to recognize a vehicle as such (15).
Passing sight distances calculated on this basis are also considered adequate for night conditions
127
AASHTO—Geometric Design of Highways and Streets
because headlight beams of an opposing vehicle generally can be seen from a greater distance
than a vehicle can be recognized in the daytime. The choice of an object height equal to the driver
eye height makes passing sight distance design reciprocal (i.e., when the driver of the passing
vehicle can see the opposing vehicle, the driver of the opposing vehicle can also see the passing
vehicle).
Sight Obstructions
On a tangent roadway, the obstruction that limits the driver's sight distance is the road
surface at some point on a crest vertical curve. On horizontal curves, the obstruction that limits
the driver's sight distance may be the road surface at some point on a crest vertical curve, or it
may be some physical feature outside of the traveled way, such as a longitudinal barrier, a bridge -
approach fill slope, a tree, foliage, or the backslope of a cut section. Accordingly, all highway
construction plans should be checked in both the vertical and horizontal plane for sight distance
obstructions.
Measuring and Recording Sight Distance on Plans
The design of horizontal alignment and vertical profile using sight distance and other criteria
is addressed later in this chapter, including the detailed design of horizontal and vertical curves.
Sight distance should be considered in the preliminary stages of design when both the horizontal
and vertical alignment are still subject to adjustment. By determining the available sight distances
graphically on the plans and recording them at frequent intervals, the designer can appraise the
overall layout and effect a more balanced design by minor adjustments in the plan or profile.
Methods for scaling sight distances on plans are demonstrated in Exhibit 3-8, which also shows a
typical sight distance record that would be shown on the final plans.
Because the view of the highway ahead may change rapidly in a short distance, it is desirable
to measure and record sight distance for both directions of travel at each station. Both horizontal
and vertical sight distances should be measured and the shorter lengths recorded. In the case of a
two-lane highway, passing sight distance should be measured and recorded in addition to
stopping sight distance.
Sight distance information, such as that presented in Exhibits 3-70 and 3-73, may be used to
establish minimum lengths of vertical curves. Charts similar to Exhibit 3-53 are useful for
determining the radius of horizontal curve or the lateral offset from the traveled way needed to
provide the design sight distance. Once the horizontal and vertical alignments are tentatively
established, the most practical means of examining sight distances along the proposed highway is
by direct scaling on the plans.
Horizontal sight distance on the inside of a curve is limited by obstructions such as
buildings, hedges, wooded areas, high ground, or other topographic features. These are generally
plotted on the plans. Horizontal sight is measured with a straightedge, as indicated in the upper
left portion of Exhibit 3-8. The cut slope obstruction is shown on the worksheets by a line
128
Intersections
- r ...
the traffic control devices and not by the presence or absence of vehicles on the intersecting
approaches.
rr
Departure Sight Triangles
A second type of clear sight triangle provides sight distance sufficient for a stopped driver on
a minor -road approach to depart from the intersection and enter or cross the major road.
Exhibit 9-50B shows typical departure sight triangles to the left and to the right of the location of
a stopped vehicle on the minor road. Departure sight triangles should be provided in each
quadrant of each intersection approach controlled by stop or yield signs. Departure sight triangles
should also be provided for some signalized intersection approaches (see Case D in the section on
"Intersection Control").
The recommended dimensions of the clear sight triangle for desirable traffic operations
where stopped vehicles enter or cross a major road are based on assumptions derived from field
observations of driver gap -acceptance behavior (10). The provision of clear sight triangles like
those shown in Exhibit 9-50B also allows the drivers of vehicles on the major road to see any
vehicles stopped on the minor -road approach and to be prepared to slow or stop, if necessary.
Identification of Sight Obstructions within Sight Triangles
The profiles of the intersecting roadways should be designed to provide the recommended
sight distances for drivers on the intersection approaches. Within a sight triangle, any object at a
height above the elevation of the adjacent roadways that would obstruct the driver's view should
be removed or lowered, if practical. Such objects may include buildings, parked vehicles,
highway structures, roadside hardware, hedges, trees, bushes, unmowed grass, tall crops, walls,
fences, and the terrain itself Particular attention should be given to the evaluation of clear sight
triangles at interchange ramp/crossroad intersections where features such as bridge railings, piers,
and abutments are potential sight obstructions.
The determination of whether an object constitutes a sight obstruction should consider both
the horizontal and vertical alignment of both intersecting roadways, as well as the height and
position of the object. In making this determination, it should be assumed that the driver's eye is
1 080 mm [3.5 ft] above the roadway surface and that the object to be seen is 1 080 mm [3.5 ft]
above the surface of the intersecting road.
This object height is based on a vehicle height of 1 330 mm [4.35 ft], which represents the
15th percentile of vehicle heights in the current passenger car population less an allowance of
250 mm [10 in]. This allowance represents a near -maximum value for the portion of a passenger
car height that needs to be visible for another driver to recognize it as the object. The use of an
object height equal to the driver eye height makes intersection sight distances reciprocal (i.e., if
one driver can see another vehicle, then the driver of that vehicle can also see the first vehicle).
653
AASHTO—Geometric Design of Highways and Streets
Where the sight -distance value used in design is based on a single -unit or combination truck
as the design vehicle, it is also appropriate to use the eye height of a truck driver in checking sight
obstructions. The recommended value of a truck driver's eye height is 2 330 mm [7.6 ft] above
the roadway surface.
Intersection Control
The recommended dimensions of the sight triangles vary with the type of traffic control used
at an intersection because different types of control impose different legal constraints on drivers
and, therefore, result in different driver behavior. Procedures to determine sight distances at
intersections are presented below according to different types of traffic control, as follows:
Case A —Intersections with no control
Case B—Intersections with stop control on the minor road
Case B 1—Left turn from the minor road
Case 132—Right turn from the minor road
Case 133—Crossing maneuver from the minor road
Case C—Intersections with yield control on the minor road
Case C1—Crossing maneuver from the minor road
Case C2—Left or right turn fi-om the minor road
Case D—Intersections with traffic signal control
Case E—Intersections with all -way stop control
Case F—Left turns from the major road
Case A —Intersections with No Control
For intersections not controlled by yield signs, stop signs, or traffic signals, the driver of a
vehicle approaching an intersection should be able to see potentially conflicting vehicles in
sufficient time to stop before reaching the intersection. The location of the decision point
(driver's eye) of the sight triangles on each approach is determined from a model that is
analogous to the stopping sight distance model, with slightly different assumptions.
While some perceptual tasks at intersections may need substantially less time, the detection
and recognition of a vehicle that is a substantial distance away on an intersecting approach, and is
near the limits of the driver's peripheral vision, may take up to 2.5 s. The distance to brake to a
stop can be determined from the same braking coefficients used to determine stopping sight
distance in Exhibit 3-1.
Field observations indicate that vehicles approaching uncontrolled intersections typically
slow to approximately 50 percent of their midblock running speed. This occurs even when no
potentially conflicting vehicles are present (10). This initial slowing typically occurs at
deceleration rates up to 1.5 m/sz [5 ft/S2]. Deceleration at this gradual rate has been observed to
begin even before a potentially conflicting vehicle comes into view. Braking at greater
deceleration rates, which can approach those assumed in stopping sight distance, can begin up to
2.5 s after a vehicle on the intersecting approach comes into view. Thus, approaching vehicles
654
Intersections
Design
speed
20
30
40
50
60
70
80
90
100
110
120
130
Metric
Intersection sight
Stopping distance for
sight passenger cars
distance Calculated Design
(m7
20
35
50
65
85
105
130
160
185
220
250
285
fm}
41.7
62.6
83.4
104.3
125.1
146.0
166.8
187.7
208.5
229.4
250.2
271.1
45
65
85
105
130
150
170
190
210
230
255
275
uS Customary
Intersection
sight
Stopping
distance for
Design
sight
passen
er cars
speed
distance
Calculated
Design
(mph)
(ft)
fit
ft
15
80
165.4
170
20
115
220.5
225
25
155
275.6
280
30
200
330.8
335
35
250
385.9
390'
40
305
441.0
445
45
360
496.1
500
50
425
551.3
555
55
495
606.4
610
60
570
661.5
665
65
645
716.6
720
70
730
771.8
775
75
820
826.9
830
80
910
882.0
885
Note: Intersection sight distance shown is for a stopped passenger car to turn left onto a
two-lane highway with no median and grades 3 percent or less. For other conditions,
the time gap must be adjusted and required sight distance recalculated.
Exhibit 9-55. Design Intersectiion Sight Distance Case Bl—Left Turn from Stop
Sight distance design for left turns at divided -highway intersections should consider multiple
design vehicles and median width. If the design vehicle used to determine sight distance for a
divided -highway intersection is larger than a passenger car, then sight distance for left turns will
need to be checked for that selected design vehicle and for smaller design vehicles as well. If the
divided -highway median is wide enough to store the design vehicle with a clearance to the
through lanes of approximately 1 m [3 ft] at both ends of the vehicle, no separate analysis for the
departure sight triangle for left turns is needed on the minor -road approach for the near roadway
to the left. In most cases, the departure sight triangle for right turns (Case B2) will provide
sufficient sight distance for a passenger car to cross the near roadway to reach the median.
Possible exceptions are addressed in the discussion of Case B3.
If the design vehicle can be stored in the median with adequate clearance to the through
lanes, a departure sight triangle to the right for left turns should be provided for that design
vehicle turning left from the median roadway. Where the median is not wide enough to store the
design vehicle, a departure sight triangle should be provided for that design vehicle to turn left
from the minor -road approach.
The median width should be considered in determining the number of lanes to be crossed.
The median width should be converted to equivalent lanes. For example, a 7.2-m [24-ft] median
should be considered as two additional lanes to be crossed in applying the multilane highway
adjustment for time gaps in Exhibit 9-54. Furthermore, a departure sight triangle for left turns
661
AASHTO--Geometric vesign of Highways and Streets
Time gap (tg) (seconds) at design
Design vehicle seed of major road
Passenger car 6.5
Single -unit truck 8.5
Combination truck 10.5
Note: Time gaps are for a stopped vehicle to turn right onto or cross a
two-lane highway with no median and grades 3 percent or less.
The table values require adjustment as follows:
For multilane highways:
For crossing a major road with more than two lanes, add
0.5 seconds for passenger cars and 0.7 seconds for trucks
for each additional lane to be crossed and for narrow
medians that cannot store the design vehicle.
For minor road approach grades:
If the approach grade is an upgrade that exceeds
3 percent, add 0.1 seconds for each percent grade.
Exhibit 9-57. Time Gap for Case B2-Right Turn from Stop
and Case B3-Crossing Maneuver
Metric
US Customary
Intersection sight
Intersection sight
Stopping
distance for
Stopping
distance for
Design
sight
passenger
cars
Design
sight
passenger
cars
speed
distance
Calculated
Design
speed
distance
Calculated
Design
(km/h)
(m)
(m)
(m)
(mph)
(ft)
ft
ft
20
20
36.1
40
15
80
143.3
145
30
35
54.2
55
20
115
191.1
195
40
50
72.3
75
25
155
238.9
240
50
65
90.4
95
30
200
286.7
290
60
85
108.4
110
35
250
334.4
335
70
105
126.5
130
40
305
382.2
385
80
130
144.6
145
45
360
430.0
430
90
160
162.6
165
50
425
477.8
480
100
185
180.7
185
55
495
525.5
530
110
220
198.8
200
60
570
573.3
575
120
250
216.8
220
65
645
621.1
625
130
285
234.9
235
70
730
668.9
670
75
820
716.6
720
80
910
764.4
765
Note: Intersection sight
distance shown is for a stopped passenger car to turn
right onto or
cross a
two-lane highway with no median and grades 3 percent or less. For other conditions, the time
gap
must be adjusted and required sight distance recalculated.
Exhibit 9-58. Design Intersection Sight Distance -Case B2-Right Turn from Stop and
Case B3--Crossing Maneuver
INTERSECTION SIGHT DISTANCE WORKSHI�R)
' 1 5n Accordance with AASHTO's
A Policy on Gec,_tetric Design of Highways and Streets, 2001
1. INPUT
-----------------------------------------------------------------------------
Inters
Subjec
Commen
By:
Design Vehicle (P, SU, Other):
Design Vehicle Length: 19 ft
Assumed Turning Radius (Center of Vehicle): 20.5 ft
Approaches Speed Grade Ratio
------ ----- (Ex 9-53)
Approaching Intersection: So= Go= 1.0
Approaching from Right: Sr= Gr= 0.9
Approaching from Left: S1= G1= 1.0
Deflection Angle: Degrees Radians
To Turn Right: Ar= 1.571
To Cross: Ac= 0
To Turn Left: A1= 1.571
Cross Section of Major Street:
Distance from Stop Bar, curbline, or edge of Pavement to:
Nearest edge of opposing lanes on left: D1=]23.0
ft
Farthest edge of opposing lanes on left:; D2=_ ft
Center of nearest left -turn receiving lane: D3=1h ft
Center of nearest lane on right approach: D4= ft
Farthest edge of opposing lanes on right: D5= ft
Cross Section of Subject Approach:
Distance from right curbline or edge of pavement to:
Center of nearest lane entering approach: D6=ft
2.- SUMMARY Distance measured from intersection of vehicle paths!
-----------------------------------------------------------------------------
CASE Left from Right from Minor Left from
Minor (Dl) Minor (Dr) (Dm) Major (Do)
A 115 ft 104 ft 115 ft NA
B1 284 ft 283 ft NA NA
B2 238 ft NA NA NA
B3 248 ft 263 ft NA NA
Cl 248 ft 263 ft 130 ft NA
C2 301 ft 293 ft 82 ft NA
F NA NA NA 220 ft
INTERSECTI(:- 'SIGHT DISTANCE WORKSHEET
In Acc.-dance with AASHTO's
Page 2 of 5
A Policy on Geometric Design of
Highways and Streets,'2001
**********************************************************************************
3. CASE A - NO CONTROL
-----------------------------------------------------------------------------
Approach Speed
Distance
Grade
Distance
(Ex. 9-51)
Ratio
Major from left 25 mph
115 ft *
1.0 =
115
ft
Major from right 25 mph
115 ft *
0.9 =
103.5
ft
Minor 25 mph
115 ft *
1.0 =
115
ft
4. CASE B1 - LEFT TURN FROM STOP -CONTROLLED MINOR ROAD
----------------------------------------------------------------------------
From Left
----------------------------------------------------------------------------
tg for P vehicle =
7.5 sec
Adjustment for additional lanes =
0.3 =
0.5 *
0.5
Adjustment for approach grade =
0.0 =
0.2 *
0.0
Total tg =
7.8 sec
ISD = 1.47 * Vmajor * tg = 1.47
----------------------------------------------------------------------------
* 25 *
7.8 =
284
ft
From Right
----------------------------------------------------------------------------
tg for P vehicle =
7.5 sec
Adjustment for additional lanes =
0.2 =
0.5 *
0.4
Adjustment for approach grade =
0.0 =
0.2 *
0.0
Total tg =
7.7 sec
ISD = 1.47 * Vmajor * tg = 1.47
* 25 *
7.7 =
283
ft
5. CASE B2 - RIGHT TURN FROM STOP -CONTROLLED MINOR ROAD
-----------------------------------------------------------------------------
tg for P vehicle =
6.5 sec
Adjustment for approach grade =
0.0 =
0.2 *
0.0
Total tg =
6.5 sec
ISD = 1.47 * Vmajor * tg = 1.47
* 25 *
6.5 =
238.3
ft
INTERSECTION SIGHT DISTANCE WORKSHEET
Ir 'ccaxdance with AASHTO's
Page 3 of 5
A Policy on GeameLaic Design of Highways and Streets, 2001
**********************************************************************************
6. CASE B3 - CROSSING
FROM STOP -CONTROLLED MINOR ROAD
-----------------------------------------------------------------------------
To Right:
-----------------------------------------------------------------------------
tg for P
vehicle = 6.5 sec
Adjustment
for additional lanes = 0.7 =
0.5 *
1.3
Adjustment
for approach grade = 0.0 =
0.2 *
0.0
Total tg =
7.2 sec
ISD = 1.47
* Vmajor * tg = 1.47 * 25 *
7.2 =
263 ft
-----------------------------------------------------------------------------
To Left:
-----------------------------------------------------------------------------
tg for P
vehicle w 6.5 sec
Adjustment
for additional lanes = 0.3 =
0.5 *
0.5
Adjustment
for approach grade = 0.0 =
0.2 *
0.0
Total tg =
6.8 sec
ISD = 1.47
* Vmajor * tg = 1.47 * 25 *
6.8 =
248 ft
INTERSECTIC' SIGHT DISTANCE WORKSHEET
In A=__dance with AASHTO's Page 4 of 5
A Policy on Geometric Design of Highways and Streets, 2001
**********************************************************************************
7. CASE Cl - CROSSING FROM YIELD -CONTROLLED MINOR ROAD
----------------------------------------------------------------------------
Minor Road Approach
----------------------------------------------------------------------------
Minor Road Approach (Ex 9-60) _
Grade Adjustment Factor (Ex 9-53) _
Adjusted Length on Minor Road =
------------------------------------
Major Road Approach on Left
------------------------------------
tg = to + (w +La) / (0.88 * Vminor)
tg = 4+ ( 18+
tg = 5.7 sec
tg from Stop Control = 6.8 sec
Use tg = 6.8 sec
b = 1.47 * Vmajor * tg
b = 1.47 * 25 * 6.8
---------------------------------------
Major Road Approach on Right
tg = to + (w +La) / (0.88 * Vminor)
tg = 4+ ( 28+
tg = 6.1 sec
tg from Stop Control = 7.2 sec
Use tg = 7.2 sec
Length Time
130 ft 4.0 sec
1.0 1.0
130 ft 4 sec
------------------------------
b = 1.47 * Vmajor * tg
b = 1.47 * 25 * 7.2 =
19 ) / (0.88 * 25 )
248 ft
----------------------------
19 ) / (0.88 * 25 )
263 ft
INTERSECTION SIGHT DISTANCE WORKSHEET
Ir-',ccordance with AASHTO's Page 5 of 5
A Policy on GeomeG_ic Design of Highways and Streets, 2001
**********************************************************************************
8. CASE C2 - LEFT OR RIGHT TURN FROM YIELD -CONTROLLED MINOR ROAD
----------------------------------------------------------------------------
Minor Road Approach
----------------------------------------------------------------------------
Minor Road Approach = 82 ft 4.0 sec
Grade Adjustment Factor (Ex 9-53) = 1.0 1.0
Adjusted Length on Minor Road = 82 ft 4 sec
-----------------------------------------------------------------------------
Major Road Approach on Left
-----------------------------------------------------------------------------
tg for P vehicle = 8.0 sec
Adjustment for additional lanes = 0.2 = 0.5 * 0.4
Adjustment for approach grade = 0.0 = 0.2 * 0..0
Total tg = 8.2 sec
ISD = 1.47 * Vmajor * tg = 1.47 * 25 * 8.2 = 301 ft
Major Road Approach on Right
tg for P vehicle = 8.0 sec
Adjustment for approach grade = 0.0 = 0.2 * 0.0
Total tg = 8.0 sec
ISD = 1.47 * Vmajor * tg = 1.47 * 25 * 8.0 = 293.3 ft
9. CASE F - LEFT TURNS FROM MAJOR ROAD
-----------------------------------------------------------------------------
tg for P vehicle = 5.5 sec
Adjustment for additional lanes = -0.3 = 0.5 * -0.6
Adjustment for approach grade = 0.8 = 0.2 * 4.0
Total tg = 6.0 sec
ISD = 1.47 * Vmajor * tg = 1.47 * 25 * 6.0 = 220 ft
"�n Accordance with AASHTO's I
A Policy on Geumetric Design of Highways and Streets, 2001
**********************************************************************************
1. INPUT
----_- ------_------___-----------------
Intersection: S 296 St 0 Cantu SP E Dwy
Subject Approach: North Comments:- Pxop•osed
By;LR
P Date: 15 May 2008
Design Vehicle (P, SU, Other):iuu
Design Vehicle Length: 19 ft
Assumed Turning Radius (Center of Vehicle): 20.5 ft
Approaches Speed Grade Ratio
------ ------ (Ex 9-53)
Approaching Intersection: So= Go= 1.0
Approaching from Right: Sr= Gr= 0.9
.Approaching from Left: S1= G1= 1.0
Deflection Angle: Degrees Radians
To Turn Right: Ar= 90, 1.571
To Cross: Ac= 0. 0
To Turn Left: Al=jk; 90 1.571
Cross Section of Major Street:
Distance from Stop Bar, curbline, or edge of Pavement to:
_
Nearest edge of opposing lanes on left:
D1=
0.
ft
Farthest edge of opposing lanes on left:
D2=
1.8.0
ft
Center of nearest left -turn receiving lane:
D3=
23.0
ft
Center of nearest lane on right approach:
D4=
1123.0
ft
Farthest edge of opposing lanes on right:
D5=
20.0!ft
Cross
Section of Subject Approach:
Distance from right curbline or edge of pavement to:
Center of nearest lane entering approach:
D6=
15.0-ft
2. SUMMARY: Distance measured from intersection of vehiclepaths!
CASE
` Left from Right from Minor Left from
Minor (Dl) Minor (Dr) (Dm) Major (Do)
A
115 ft 104 ft 115 ft NA
Bl
284 ft 283 ft NA NA
B2
238 ft NA NA NA
B3
248 ft 263 ft NA NA
C1
248 ft 263 ft 130 ft NA
C2
301 ft 293 ft 82 ft NA
F
NA NA NA 220 ft
In Acco.dance with AASHTO's
Page 2 of 5
A Policy on Geometric Design of
Highways and Streets, 2001
**********************************************************************************
3. CASE A - NO CONTROL
-----------------------------------------------------------------------------
Approach Speed
Distance
Grade
Distance
(Ex. 9-51)
Ratio
Major from left 25 mph
115 ft *
1.0 =
115
ft
Major from right 25 mph
115 ft *
0.9 =
103.5
ft
Minor 25 mph
115 ft *
1.0 =
115
ft
4. CASE B1 - LEFT TURN FROM STOP -CONTROLLED MINOR ROAD
----------------------------------------------------------------------------
From Left
----------------------------------------------------------------------------
tg for P vehicle =
7.5 sec
Adjustment for additional lanes =
0.3 =
0.5 *
0.5
Adjustment for approach grade =
0.0 =
0.2 *
0.0
Total tg =
7.8 sec
ISD = 1.47 * Vmajor * tg = 1.47 * 25 *
--------------------------------------------------
From Right
tg for P vehicle =
Adjustment for additional lanes =
Adjustment for approach grade =
Total tg =
7.8 = 284 ft
--------------------
---------------------------------------
7.5 sec
0.2 = 0.5 * 0.4
0.0 = 0.2 * 0.0
7.7 sec
ISD = 1.47 * Vmajor * tg = 1.47 * 25 * 7.7 = 283 ft
5. CASE B2 - RIGHT TURN FROM STOP -CONTROLLED MINOR ROAD
-----------------------------------------------------------------------------
tg for P vehicle = 6.5 sec
Adjustment for approach grade = 0.0 = 0.2 * 0.0
Total tg = 6.5 sec
ISD = 1.47 * Vmajor * tg = 1.47 * 25 * 6.5 = 238.3 ft
w
If -)cc.ordance With AASHTU'S
/
rays �i
A Policy on GeomeL-ic Design of Highways
and Streets, 2001
**********************************************************************************
6. CASE B3 - CROSSING FROM STOP -CONTROLLED
MINOR
ROAD
-----------------------------------------------------------------------------
To Right:
-----------------------------------------------------------------------------
tg for P
vehicle =
6.5
sec
Adjustment
for additional lanes =
0.7
=
0.5 *
1.3
Adjustment
for approach grade =
0.0
=
0.2 *
0.0
Total tg =
7.2
sec
ISD = 1.47
* Vmajor * tg = 1.47 *
25
*
7.2 =
263 ft
-----------------------------------------------------------------------------
To Left:
-----------------------------------------------------------------------------
tg for P
vehicle =
6.5
sec
Adjustment
for additional lanes =
0.3
=
0.5 *
0.5
Adjustment
for approach grade =
0.0
=
0.2 *
0.0
Total tg =
6.8
sec
ISD = 1.47
* Vmajor * tg = 1.47 *
25
*
6.8 =
248 ft
In Acc— dance with AASHTO's Page 4 of 5
A Policy on Geometric Design of Highways and Streets, 2001
**********************************************************************************
7. CASE Cl - CROSSING FROM YIELD -CONTROLLED MINOR ROAD
----------------------------------------------------------------------------
Minor Road Approach
----------------------------------------------------------------------------
Minor Road Approach (Ex 9-60) _
Grade Adjustment Factor (Ex 9-53)
Adjusted Length on Minor Road =
------------------------------------
Major Road Approach on Left
-----------------------------------
tg = to + (w +La) / (0.88 * Vminor)
tg = 4+ ( 18+
tg = 5.7 sec
tg from Stop Control = 6.8 sec
Use tg = 6.8 sec
b = 1.47 * Vmajor * tg
b = 1.47 * 25
------------------------------------
Major Road Approach on Right
------------------------------------
tg = to + (w +La) / (0.88 * Vminor)
tg = 4+ ( 28+
tg = 6.1 sec
tg from Stop Control = 7.2 sec
Use tg = 7.2 sec
b = 1.47 * Vmajor * tg
b = 1.47 * 25
Length Time
130 ft 4.0 sec
1.0 1.0
130 ft 4 sec
--------------------------
--------------------
19 ) / (0.88 *
6.8 = 248 ft
---------------------
19 ) / (0.88 *
7.2 = 263 ft
25 )
25 )
INTERSECTION SIGHT DISTANCE WORKSHEET,
Ir-)ccordance with AASHTO's Page 5 of 5
A Policy on GeomeL-ic Design of Highways and Streets, 2001
**********************************************************************************
8. CASE C2 - LEFT OR RIGHT TURN FROM YIELD -CONTROLLED MINOR ROAD
----------------------------------------------------------------------------
Minor Road Approach
----------------------------------------------------------------------------
Minor Road Approach = 82 ft 4.0 sec
Grade Adjustment Factor (Ex 9-53) 1.0 1.0
Adjusted Length on Minor Road = 82 ft 4 sec
----------------------------------------------------------------------------
Major Road Approach on Left
----------------------------------------------------------------------------
tg for P vehicle = 8.0 sec
Adjustment for additional lanes = 0.2 = 0.5 * 0.4
Adjustment for approach grade = 0.0 = 0.2 * 0.0
Total tg = 8.2 sec
ISD = 1.47 * Vmajor * tg = 1.47 * 25 * 8.2 = 301 ft
Major Road Approach on Right
----------------------------------------------------------------------------
tg for P vehicle = 8.0 sec
Adjustment for approach grade = 0.0 = 0.2 * 0.0
Total tg = 8.0 sec
ISD = 1.47 * Vmajor * tg = 1.47 * 25 * 8.0 = 293.3 ft
9. CASE F - LEFT TURNS FROM MAJOR ROAD
-----------------------------------------------------------------------------
tg for P vehicle = 5.5 sec
Adjustment for additional lanes = -0.3 = 0.5 * -0.6
Adjustment for approach grade = 0.8 = 0.2 * 4.0
Total tg = 6.0 sec
ISD = 1.47 * Vmajor * tg = 1.47 * 25 * 6.0 = 220 ft
CITY OF
A. Federal Way
June 3, 2008
Mr. Leighton O'Brien
1433 SW 340' Place
Federal Way, WA 98023
RE,- Permit No, 08-102166-00 SM
Cantu Short Plat - 1846 S 29e Street
Sight Distance Variance Request
Dear Mr. O'Brien:
CITY HALL
33325 8th Avenue South
Mailing Address: PO Box 9718
Federal Way, WA 98063-9718
(253) 835-7000
wwwcityoffederalway.coin
�0'
Staff has evaluated your site distance analysis for the Cantu Short Plat. All new access points
created by the proposed plat must meet both stopping and intersection sight distance
requirements in accordance with AASHTO's "A Policy on Geometric Design of Highways and
Streets", 2001.
The City allows sight distance analyses to be based on the posted speed limit, which in this case
is 25 mph. Based on the posted speed limit, it appears that your proposed driveway location
meets stopping site distance requirements, but as you noted, does not meet intersection site
distance requirements. Therefore, the access point must be modified or relocated such that all
sight distance requirements can be met.
Although the driveway serving the existing single family home does not meet sight distance
requirements, it is pre-existing and can continue to be used as an access point serving one unit.
Should you have any questions, please feel free to contact me at (253) 835-2730.
Sincerely,
William Appleto , P.F.
Development Services Manager
WA:cc
cc: Project File / WA
Day File
L:\CSDC\DOCS\SAVE\16300274044.DOC