Geometric Review and Design (GRAD) 3...Spiral Curves 3 16| Module 3 –Horizontal Alignment ODOT L&D...
Transcript of Geometric Review and Design (GRAD) 3...Spiral Curves 3 16| Module 3 –Horizontal Alignment ODOT L&D...
Geometric Review and Design (GRAD)
Horizontal
Alignment
3
32 | Module 3 – Horizontal Alignment
ODOT L&D Vol. 1 – Section 200
Identify the Design Elements of Horizontal Alignments
Understand how to Design Horizontal Alignments to a Given Design Speed
Understand how to design appropriate superelevation design
Learning Objectives
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Tangents
Circular Curves
Spiral (Transition) Curves
Superelevation
Elements of Horizontal Alignments
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Sect 202
Maximum Deflection without
Horizontal Curve
Angle varies with the design speed of the roadway
Recommended Minimum Distance
between Consecutive Horizontal
Deflections
High speed / Low speed
Horizontal Alignments - Curves
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Horizontal Alignments - Curves
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Horizontal Alignments - Curves
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Types of Curves
Simple Curves
Compound Curves
Reverse Curves
Spiral Curves
Horizontal Alignments - Curves
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Key Elements of a Horizontal
Curve
Simple Curves
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Degree vs. Radius
Degree of curve is the central angle subtended by a 100-foot arc for a given radius.
Example: Degree of curve for R = 1909 feet
Simple Curves
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Degree vs. Radius
Degree of curve is the central angle subtended by a 100-foot arc for a given radius.
Example: Degree of curve for R = 1909 feet
D = 3°
Simple Curves
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Degree vs. Radius
Degree of curve is the central angle subtended by a 100-foot arc for a given radius.
Example: Degree of curve for R = 1909 feet
D = 3°
Example: Radius of curve for D = 9.5°
Simple Curves
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Degree vs. Radius
Degree of curve is the central angle subtended by a 100-foot arc for a given radius.
Example: Degree of curve for R = 1909 feet
D = 3°
Example: Radius of curve for D = 9.5°
R = 603 feet
Simple Curves
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2 horizontal curves in the same
direction
Utilize a common tangent
From AASHTO: It is preferable that the
ratio of the flatter radius to the
sharper radius not exceed 2:1 *
Should be used with caution!
Compound Curves
* A Policy on Geometric Design of Highways and Streets, 7th
Edition (2018) - Section 3.3.7.3
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2 horizontal curves in opposite directions separated by a tangent with sufficient length to rotate superelevation from one curve to the next.
Superelevation - The cross slope of the pavement used to compensate for the effect of centrifugal force on horizontal curves
Reverse Curves
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Combination of high speed and
sharp curvature leads to longer
transition paths, which can result in
shifts in lateral position and
sometimes actual encroachment
into adjacent lanes.
Should be used on new alignments
based on the maximum degree of
curve as shown in Figure 202-11.
Length of spiral should be equal or
greater than superelevation runoff
length for the curve.
Spiral Curves
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Spiral Curves
Key Elements of a Spiral
Curve
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Sect 202.4
Increasing the cross slope to
keep vehicles on the road
through the horizontal
curve
Implemented by raising the
pavement outer edge with
respect to the inner edge.
Superelevation
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Recommended rates
Rural Highways (0.08 max) –
Figure 202-7
Urban Highways (high speed – 0.06
max) – Figure 202-8
Urban Ramps and Interchange
(low speed – 0.06 max) – Figure
202-10
Urban Highways (low speed – 0.04
max) – Figure 202-9; Figure 202-9a
Superelevation
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Can be difficult to apply
recommended superelevation rates
on urban roadways because of:
Wide pavements
Adjacent development
Drainage conditions
Frequent access points
In these cases, may use reduced or
no superelevation although Crown
Removal is recommended min.
Superelevation – 0.04 Figure
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Required whenever rate specified in Figures 202-7 through 202-10 is not provided.
Not required if a higher superelevation rate than what is specified in Figures 202-7 through 202-10 is provided as long as the rate doesn’t exceed the maximum superelevation rate for that given figure.
Superelevation – Design Exceptions
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Maximum curvature (minimum
curve radius) that doesn’t
require superelevation based on
design speed and rural/urban
condition (Figure 202-3)
Can also use Figures 202-7, 202-
8, and 202-9 to determine these
values.
Maximum Curvature without Superelevation
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Figures also show maximum
curvature for given design speed
(confirmed in Figure 202-2)
Maximum Curvature without Superelevation
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Four methods:
1. Revolve pavement about the
centerline (most commonly used)
2. Revolve pavement about the inner
edge of traveled way
3. Revolve pavement about the outer
edge of traveled way
4. Revolve pavement having a straight
cross slope (no crown) about the
outside edge of traveled way (ramps
typically)
Superelevation Methods
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Key Terms:
Normal Crown (Point A)
Adverse Crown Removed (Point B; also known as “half flat”)
Crown Removal (Point C)
PC/PT of curve (Point D) Superelevation rate is 50-70% design rate
Full Super (Point E) Design superelevation rate
Tangent Runout Normal Crown to Adverse Crown Removed
Superelevation Runoff Adverse Crown Removed to Full Super
Superelevation Transitions
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With Spirals
Transition from Adverse Crown
Removed to Full Super shall occur
within the limits of the spiral.
Superelevation Position Spiral Length
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With Spirals
Transition from Adverse Crown
Removed to Full Super shall occur
within the limits of the spiral.
Simple Curves – No Spirals
50%-70% of maximum
superelevation rate is outside the
curve limits; 2/3 of
superelevation rate at PC and PT
Prefer to have full superelevation
rate maintained for 1/3 of curve
length
Superelevation Position
2/3 (e(des) rate)
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Determine width of pavement
that is being rotated
Superelevation Transitions
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Determine width of pavement
that is being rotated
Identify Adjustment Factor (bw)
“Credit” for rotating more than
one lane
Superelevation Transitions
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Determine width of pavement
that is being rotated
Identify Adjustment Factor (bw)
“Credit” for rotating more than
one lane
Identify Equivalent Slope Rate (G)
For the given Design Speed
Superelevation Transitions
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Determine width of pavement
that is being rotated
Identify Adjustment Factor (bw)
“Credit” for rotating more than
one lane
Identify Equivalent Slope Rate (G)
For the given Design Speed
Calculate Superelevation Runoff
(Lr)
Superelevation Transitions
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Determine width of pavement
that is being rotated
Identify Adjustment Factor (bw)
“Credit” for rotating more than
one lane
Identify Equivalent Slope Rate (G)
For the given Design Speed
Calculate Superelevation Runoff
(Lr)
Calculate Tangent Runout (Lt)
Superelevation Transitions
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Example - Determine Superelevation
Degree of Curve = 3.0°
Design Speed = 60 mph
Urban Location
Superelevation
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Example - Determine Superelevation
Degree of Curve = 3.0°
Design Speed = 60 mph
Urban Location
Radius of Curve = 1,910 feet
Superelevation
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Example - Determine Superelevation
Degree of Curve = 3.0°
Design Speed = 60 mph
Urban Location
Radius of Curve = 1,910 feet
e(des) = 0.055 ft/ft
Superelevation
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Example - Determine Superelevation
Radius of Curve = 1,550 feet
Design Speed = 50 mph
Urban Location
Superelevation
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Example - Determine Superelevation
Radius of Curve = 1,550 feet
Design Speed = 50 mph
Urban Location
Degree of Curve = 3°42’
Superelevation
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Example - Determine Superelevation
Radius of Curve = 1,550 feet
Design Speed = 50 mph
Urban Location
Degree of Curve = 3°42’
e(des) = 0.050 ft/ft
Superelevation
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Example – determine
superelevation rotation
placement
Design Speed = 50 mph
Undivided Highway
Rotate 2-12’ lanes
PC Station = 100+73.35
e(des) = 0.050 ft/ft
Superelevation Transitions
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Example – determine
superelevation rotation
placement
Design Speed = 50 mph
Undivided Highway
Rotate 2-12’ lanes
PC Station = 100+73.35
e(des) = 0.050 ft/ft
Superelevation Transitions or
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Example – determine
superelevation rotation
placement
Design Speed = 50 mph
Undivided Highway
Rotate 2-12’ lanes
PC Station = 100+73.35
e(des) = 0.050 ft/ft
Superelevation Transitions or
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ODOT L&D Vol. 1 – Section 200
Example – determine
superelevation rotation
placement
Design Speed = 50 mph
Undivided Highway
Rotate 2-12’ lanes
PC Station = 100+73.35
e(des) = 0.050 ft/ft
Superelevation Transitions
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Example – determine
superelevation rotation
placement
Design Speed = 50 mph
Undivided Highway
Rotate 2-12’ lanes
PC Station = 100+73.35
e(des) = 0.050 ft/ft
Superelevation Transitions
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Example – determine
superelevation rotation
placement
Design Speed = 50 mph
Undivided Highway
Rotate 2-12’ lanes
PC Station = 100+73.35
e(des) = 0.050 ft/ft
Superelevation Transitions
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Example – determine
superelevation rotation
placement
Design Speed = 50 mph
Undivided Highway
Rotate 2-12’ lanes
PC Station = 100+73.35
e(des) = 0.050 ft/ft
Superelevation Transitions
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ODOT L&D Vol. 1 – Section 200
Example – determine
superelevation rotation
placement
Design Speed = 50 mph
Undivided Highway
Rotate 2-12’ lanes
PC Station = 100+73.35
e(des) = 0.050 ft/ft
Superelevation Transitions
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Example – determine
superelevation rotation
placement
Design Speed = 50 mph
Undivided Highway
Rotate 2-12’ lanes
PC Station = 100+73.35
e(des) = 0.050 ft/ft
Superelevation Transitions
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Each curve has its own superelevation runoff value
New Alignments
PT and PC should be separated enough
for a smooth transition at a rate not
to exceed “G” value in Figure 202-4.
Distance to be not less than 50% nor
greater than 70% of Lr1 + Lr2. 2/3
(67%) is preferred.
Existing Alignments
Conform as closely as possible to New
Alignments criteria.
Superelevation - Reverse Curves
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Example – determine
superelevation rotation
placement
Design Speed = 50 mph
Undivided Highway
Rotate 2-12’ lanes
PC Station = 100+73.35
e(des) = 0.050 ft/ft
Superelevation Transitions
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Superelevation Exaggerated Profiles
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Superelevation Exaggerated Profiles
Y = (enc) X
(rotating pavement width)
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Superelevation Exaggerated Profiles
Y = (enc) X
(rotating pavement width)
Y = (FS cross slope) X
(rotating pavement width)
Y = (-FS cross slope) X
(rotating pavement width)
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ODOT L&D Vol. 1 – Section 200
Superelevation Exaggerated Profiles
Y = (enc) X
(rotating pavement width)
Y = (FS cross slope) X
(rotating pavement width)
Y = (-FS cross slope) X
(rotating pavement width)
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Superelevation Exaggerated Profiles
Y = (enc) X
(rotating pavement width)
Y = (FS cross slope) X
(rotating pavement width)
Y = (-FS cross slope) X
(rotating pavement width)
PC = 2/3 x Superelevation Rate)
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ODOT L&D Vol. 1 – Section 200
Superelevation Exaggerated Profiles
Y = (enc) X
(rotating pavement width)
Y = (FS cross slope) X
(rotating pavement width)
Y = (-FS cross slope) X
(rotating pavement width)
PC = 2/3 x Superelevation Rate)L = [(ePC/eDES) x Lr]
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Superelevation Exaggerated Profiles
Y = (enc) X
(rotating pavement width)
Y = (FS cross slope) X
(rotating pavement width)
Y = (-FS cross slope) X
(rotating pavement width)
PC = 2/3 x Superelevation Rate)L = [(ePC/eDES) x Lr]
L = Lt L = Lt
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Superelevation Exaggerated Profiles
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Information reviewers
should look for:
Superelevation Rate
Transition Length
Transition Rate
Super Rate at PC
Super Rate at PT
Length of curve/time at full superelevation
Superelevation Review
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For horizontal alignment
design elements that
don’t meet standards
Chevrons
Rumble Strips
Curve Ahead Signage
Curve Widening
Place the wider shoulder on the left (instead of right) side
Safety Countermeasures
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Key Terms
Horizontal Alignments
Tangents
Curves
Spirals
Horizontal Curves
Simple Curves
Compound Curves
Reverse Curves
Spiral Curves
Tangent Runout (NC to ACremoved)
Superelevation Runoff (ACremoved to FS)
Module Review