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To: Ed Zdenek , ?'::'FK
Rick En=dorff, Fort Collins Traffic Engineer
From: Hatt Crel ich
Date: February 1
Subject: Harmony Road right-in/right-out access to thc•
McDonald' _.i te- -
This memorandum documents rrry research and analysis
with regard to the proposed Harmony Road right-in/right-
out .acre_._ to the 1'1cDon•a.ld" _ site. City Staff requested
information regarding the deceleration lane geometrics.
for this access point. The design '_.Feed for Ha.rmon;:
Road was assumed to be 35 mph which is the existing
posted _.peed of the street. The proposed access i
between College Avenue .and Mason Street. The centerline
distance between these two streets is 540 feet. It i
.assumed that the City Staff would require a. "pedestrian
bulb" at the College Harmony intersection. This would
require that the taper for the deceleration lane could
begin no closer than 50 feet from the flaw line on the
west side i rf College Avenue. I deal 1 y, the C i ty Staff
would d like the proposed right—in/right-out access
designed to criteria set forth in the State Highway
Access Code. If
standards t andard can not bmet,
a r1�e t , other
criteria/standards/examples shaul d be provided with
regard to the necessary deceleration lane.
For the 35 mph design speed, the State Highway
Access Code requires adeceleration lane 4t 235 feet
plus 120 feet of taper. (total - 55 feet) using .a 15 mph
turn at the access point. A 15 mph turn requires 3. curb
return radius of 40 feet. The deceleration lane based
upon these criteria would place the right.-in/right-out
acre_._ approximately 70 feet from the centerline of
Mason Street, This is unacceptable to all parties
concerned with this access.
In order to have .a, developable lot on the northeast
earner of the Harmony/Mason intersection, the centerline
of the proposed right-in/right-out access must be
approximately 150 feet east of the east right-of-way of
Mason Street. Assuming a 30 firirt wide access, a, total
of 1 95 feet are available for deceleration and taper.
According to Design Criteria and St.a.ndard=• for Streets,
Cit;. of Fort Collins, Jul; 1?86, Section 1.02.08,
Deceleration Lane_. - Arterial Street•_., the deceleration
lane plus taper is 250 feet for 30 mph and 370 feet for.
40 mph. Using the 10 feet (250 + 70 ; 2) for 35 mph,
it can be seen that the Fort Col 1 i n=_. standard cannot be
met. According to H Policy, on Geometric Design of
Hi Qhway•_ and streets., AASHTO, 1984, pg. 874,
"The length of the a.ux i 1 i •'try lanes for turning
vehicles cons•is.ts of three components: (1)
deceleration length, (2) storage length, and
(3) entering taper. Desirably, the total length
of the aux i 1 i ar::. 1 one _•haul d be the sum of the
length for these three components. Common
practice, however, is to accept a. moderate amount
of deceleration within the through lanes and to
consider the taper as a part of the deceleration
length. Where intersections occur as frequently
as four per mi 1 e, it is customary to forego most
of the deceleration length and to provide only
the storage length plus. taper• . "
According to Figure 1, copied from A Policy on Geometric
Design of Hiqkwa.ys. and Streets, f-+ASHTO, 1?$4, pg. 36,
the distance needed to comfortably slow a vehicle
trave l l i ng 35 mph (speed can Ha.rmony? to a. 15 mph turning
speed is 160 feet. Given th i •__•, the length of decelera-
tion lanes should be at least 160 feet. `_'since accesses.
along both of these streets are more frequent than four
per mi 1 e , this distance includes the taper. Storage
length is not required on a. right -turn lane of this type
since vehicle_ will not be delayed in entering the site.
Given that there is 1?5 feet available for deceleration
lane and taper, this distance should be used. The
portion devoted to full width deceleration lane and the
portion devoted to taper is an engineering judgment. if
the taper length is as short as possible, then the
exiting vehicle can fully uti 1 ize the full width of the
deceleration lane being ful 1 y removed from the right
through lane. This more abrupt type of design of the
taper offers improved driver commitment to the emit
maneuver and also contributes to driver security and
safety because their vehicle can be fully out of the
through lane. The shortened toper can only be
introduced at lower design speeds and in urban
situations, where frequent exits to deceleration lanes;
are common place and expected. Offering early exit to a.
full width deceleration lane could also improve the
capacity of the arterial street because the slow -down
interference to the through lane would be diminished.
Using a. symmetrical reverse curve design (from
Figure IX-65C:
in A
Policy
on Geometric Design of
Hiohw.axs and
Streets,
with a radius of 150 feet, a taper
length of Sb
feet
for
a 12 foot lane results. This
allows 109 feet
(195'
- 86') of full widtl-, deceleration
lane at this
location.
This is in excess of the minimum
b r .a k: i n g d i _. t .=-,. n c e
f or. we t F a. v e m e n t =.
a. t :" 5 rr, F. h r 1 n p f e e t —
r,:,e `r in Figure
l?. Thi=_
de=.ign
rr,ee t =. _ the cr i t.er i a i n
the H ;'_HT0 de _ i cqn
rr,a.nua.l a.nd
ca.n be
a.cccirrmmc,dated a.t the
prapc.__.ed riQht—in.:'ri
�ht —e-ut
H.armc,r,'
F.cD,.d .acce=._.,
0
C�
80
w 70
Y
Q
n
= 60
a
z
w --
I O 50
Q J
w 40
Q 31
Q Q 30
P
z
A�
X
V/
Al
i
I
p 100u 0 200 300 400 500 600
0 `-
DISTANCE TRAVELED IFTI
DECELERATION DISTANCES
FOR PASSENGER VEHICLES
APPROACHING INTERSECTIONS
SPEED nEACIIED
(COMFORTABLE "ATE)
A = 50 MP11
8 = 40 MP11
C = 30 MI'11
D - 20 MP11
E - 0 M PFI
MINIMUM BRAKING DISTANCE
X = DRYfAVEMENT
Y a WETPAVEMENT
FIGURE 1