Superelevation التعلية الجانبية
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202.4 Superelevation التعلية
الجانبية
202.4.1
Superelevation Rate
202.4.2 Effect of
Grades on Superelevation
202.4.3 Maximum Curvature Without Superelevation
(Minimum Curve Radius Without Superelevation)
202.4.4 Superelevation
Methods
202.4.5 Superelevation
Transition
202.4.6 Superelevation
Position
202.4.7 Profiles and
Elevations
202.4.8 Superelevation
Between Reverse Horizontal Curves
202.4.1 Superelevation Rate (ed) معدل التعلية
مثلا 1.7% مثلا 2.5%
Superelevation rates for horizontal curves vary with location
(urban/rural), d
egree of curvature (curve radius), and design speed.
تأثير الانحدار الطولي على التعلية الجانبية
On long and
fairly steep grades, drivers tend to travel somewhat slower in the upgrade
direction and somewhat faster in the downgrade direction than on level
roadways. In the case of divided highways, where each pavement can be
superelevated independently, or on one-way roadways, such as ramps, this tendency
should be recognized to see whether some adjustment in the superelevation rate
would be desirable and/or feasible. On grades of 4 percent or greater with a
length of 1000 ft. or more and a superelevation rate of 0.06 or more, the
designer may adjust the superelevation rate by assuming a design speed which is
5 mph less in the upgrade direction and 5 mph higher in the downgrade
direction, providing that the assumed design speed is not less than the legal
speed. On two-lane, two-way roadways and on other multi-lane undivided
roadways, such adjustments are less feasible, and should be disregarded.
أقصى تقوس مسموح بدون تعلية
202.4.3
Maximum Curvature Without Superelevation (Minimum Curve Radius Without Superelevation)
Figure 202-3 gives the maximum
degree of curvature [minimum curve radius] which does not require superelevation
based on the design speed and the rural/urban condition. This figure should be
used in conjunction with Figures 202-7, 202-8, and 202-9 to
determine at what point in the “ed” columns that superelevation becomes a design consideration. The
corresponding data for Figure 202-10 is contained on the figure
202.4.4 Superelevation Methods
Figure 202-5 shows four methods by which superelevation is developed leading into and
coming out of horizontal curves.
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• Method 1 involves revolving
the pavement about the centerline and is the most commonly used method. This
method could be applied to multi-lane divided roadway sections where the
divided segments are not crowned in a normal section. In this case, the
median pavement edge acts as the "centerline". • Method 2 shows the pavement
being revolved about the inner edge of traveled way and Method 3 uses the
outer edge of traveled way as a rotation point. Both of these methods are
used on a multi-lane divided roadway where the divided segments are crowned
in a normal section. Since the control point for revolving the pavement is
the median pavement edge, Method 2 would apply to the outer lanes and Method
3 would apply to the inner lanes. Method 2 is also used on undivided roadways
where drainage problems preclude the use of Method 1. • Method 4 revolves the pavement
having a straight cross slope about the outside edge of traveled way. Method
4 would apply to single-lane or multi-lane ramps or roadways that are not
crowned. |
 |
In reference to the above discussion on the superelevation of divided roadways, it is always preferable to use the median edge of traveled way as the rotation point. This greatly reduces the amount of distortion in grading the median area.
202.4.5 Superelevation Transition
The length of highway needed to change from a normal crown pavement
section to a fully superelevated pavement section is referred to as the
superelevation transition.
The superelevation transition is divided into two parts - the tangent
runout and the superelevation runoff. The tangent runout (”Lt”) is the length
required to remove the adverse pavement cross slope. As is shown on Method 1 of
Figure 202-5, this is the length needed to raise the "outside" edge
of traveled way from a normal slope to a half-flat section (cross section A to
cross section B of Figure 202-5, Method 1).
The superelevation runoff ("Lr") is the length required to
raise the "outside" edge of traveled way from a "half flat"
section to a fully superelevated section (cross section B to cross section E of
Figure 202-5, Method 1).
The length of transition required to remove the pavement crown is the
distance between cross section A and cross section C Figure 202-5 and is
generally equal to twice the ”Lt” distance.
The minimum superelevation transition length is determined by
multiplying the edge of traveled way correction by the equivalent slope rate ("G")
shown on Figure 202-4.
The rate of change of superelevation should be constant throughout the
transition. The values for "Lr" given in Figures 202-7, 202-8 and
202-9 are based on two 12-foot lanes revolved about the centerline.
"Lr" in Figure 202-10 is based on one 16-foot lane revolved about the
edge of traveled way.
Use the equations provided on Figure 202-4 to determine “Lr” for cases
involving other lane widths or where more than one lane is being revolved about
the centerline or baseline.
Figures 202-5a through 202-5d have been provided to show the designer
how to develop the superelevation transitions
for a two-lane undivided highway (Figure 202-5a),
a four-lane divided highway (Figure 202-5b)
and a
six-lane divided highway (Figures
202-5c & d).
Figure 202-5c could also be used for a four-lane divided highway with future median lanes
and Figure 202-5d could also be used for a four-lane divided highway with future outside lanes.
Figures 202-5a through 202-5d have been provided to show the designer
how to develop the superelevation transitions
for a two-lane undivided highway (Figure 202-5a)
a four-lane divided highway (Figure 202-5b)
and a
six-lane divided highway (Figures
202-5c & d).
Figure 202-5c could also be used for a four-lane divided highway with future median lanes
and a six-lane divided highway (Figures 202-5c &
d).
and Figure 202-5d could also be used for a four-lane divided highway with future outside lanes.
202.4.6 Superelevation Position
Figures 202-5a through 202-5d show the recommended positioning of the
proposed superelevation transition in relationship to the horizontal curve.
عند استخدام
المنحنى الانتقالي (Spiral)
For those curves with spirals, the transition from adverse crown removal
to full superelevation shall occur within the limits of the spiral. In other
words, the spiral length shall equal the "Lr" value.
المنحنيات
البسطة: بدون استخدام المنحنى الانتقالي (Spiral) 50-70 في المائة من طول الانتقال يوضع خارج
المنحنى أي في الخط المستقيم
For simple curves without spirals, the "Lr" transition shall
be placed so that 50 percent to 70 percent of the maximum superelevation rate
is outside the curve limits (P.C., P.T.). It is recommended that, whenever
possible, 2/3 of the full superelevation rate be present at the P.C. and P.T.
In addition, whenever possible, full superelevation should be maintained for at
least 1/3 the length of the curve.
