Highway Design Training Course

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Highway Design Training Course Part II
By Xudong Jia, Ph.D., PE Timothy
Romine Department of Civil Engineering California
State Polytechnic University, Pomona March 2002
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Profiles and Vertical Alignment
Elements of Profiles and Vertical
Alignments CalTrans Standards on Vertical
Alignment CalTrans Standards Used in the
Training Project Conformance Check of CalTrans
Standards
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Horizontal Alignment
A vertical alignment alignment consists of a
series of grade line segments and circular curves
Tangent line segments are easy to handle. However
the circular curves are Not. They affect
significantly the safety considerations of a
highway project and require a smooth transition
from tangent segments.
Circular Curve
Spiral
Tangent Segment
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Circular Curve in Horizontal Alignment
PI
BC
EC
R
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Superelevation emax and e
Superelevation e is a cross slope to balance the
centrifugal force emax is the maximum
superelevation rate given a certain highway
type. It varies from one highway type to another.
For Example, emax 0.10 for freeways (Page
200-9) e is the superelevation rate used in the
design e is determined based on emax and
R (Page 200-9) What is a standard
superelevation rate of freeways and expressways
with a curve radius of 400 m?
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Superelevation emax and e
What is a standard superelevation rate of
freeways and expressways with a curve radius of
400 m?
emax
0.10 from Table 202.2 Page 200-9
e
0.09 from Table 202.2 Page 200-9 with R 400 m
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Minimum Radius of Circular Curve
Table 203.2 HDM P200-16
Given emax 0.10 for freeways (Page 200-9) V
100 km/h Fs 0.12 from Page 200-10
Design Speed
Rmin
30 40 50 60 70 80 90 100 110 120 130
40 70 100 150 200 260 320 400 600 900 1200
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Superelevation Transition
Superelevation Transition should be at the two
ends of a curve It consists of crown runoff and
superelevation runoff (See Page 200-12) The
superelevation runoff has its two third on the
tangent and one third on the curve.
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Superelevation Transition
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Superelevation Transition
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Superelevation Transition (Example)
A 400-meter radius curve is followed by a
reversing curve of a 500-meter radius in a 4-lane
undivided freeway. The two curves are separated
by a tangent line of 100 meters. Does the
design conform with the design standards?
500 m
60 m
400 m
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Superelevation Transition (Solution)
500 m
A
60 m
B
400 m
A Curve emax 0.10 e 0.09 given R 400
m 2/3 Runoff 0.67 99 66.33 m B
Curve emax 0.10 e 0.07 Given R 500
m 2/3 Runoff 0.67 78 52.26 m 100 m lt
66.33 52.26 118.59 m No OK, What do we do
now?
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Superelevation Transition (Solution)
If the alignment is designed for 2-lane highways
in mountainous terrain, ramps, collector roads,
frontage roads, what do we do? Modify the rate
of change of cross slope (? 4 per 20 m)
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Stopping Sight Distance on Horizontal Curves
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SSD on Horizontal Curves (Example)
A horizontal curve with a radius of 400 meters is
designed on a two-lane highway that has design
speed of 110 km/h. If the highway is flat at the
curve section, determine the minimum distance a
large McDonalds billboard can be placed from the
center line of the inside lane of the curve,
without reducing the required SSD. Assume PIEV
time of 2.5 sec and a 3.4 m/sec2
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SSD on Horizontal Curves (Solution)
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CalTrans Standards on Horizontal Alignments
Horizontal Alignment should provide at least the
minimum SSD for the chosen design speed at all
points of the highway Curves should be designed
with their radius greater than Rmin. If Rmin
cannot provided enough lateral clearance to an
obstruction, Figure 201.6 governs. The Design
Speed between successive curves should not more
than 15 km/h due to alignment consistency When ?
lt 10, minimum curve length 240 m When ? lt
0.5, no curve is needed Compound curves should
be avoided. Rshorter 2/3Rlarger when Rshorter ?
300 m Larger radius curve follows smaller radius
curve on 2-lane highway
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CalTrans Standards on Horizontal Alignments
The connecting tangent on reversing curves should
be greater than 2/3 runoff of the first curve and
2/3 runoff of the second curve. If it is not
possible, 4 per 20 m governs. A minimum of 120 m
should be considered when feasible. Broken back
curves are not desirable.
Alignment at bridges superelevation rate on
bridge ? 10 Bridges should be out of 2/3 runoff
of the curve at two ends.
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CalTrans Standards on Horizontal Alignments
Superelevation 3000 m radius curve, no
superelevation is needed Axis of
rotation Centerline on undivided
highways Left edge of ETW on ramps and f-f
connections centerline on divided highways
with median width ? 20 m median edges
of traveled way on divided highways with
median width gt 20 m
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Design Procedures of Horizontal Alignment

• 1. Investigate and assess the characters of the
  project area
• 2. Determine individual elements of alignment
• Curve Design R min
• curve length and ?
• Superelevation
• Runoff
• Arrange Tangent Segments and Curves
• Check Conformance to Design Standards
• Sight Distance
• Superelevation

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Horizontal Alignments for Training Project
The Training Project involves the design of five
horizontal alignments One for Freeway Four
for Ramps
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Freeway Horizontal Alignment Design
Two below PIs are given in the training project
for the training project English PI 1 X
2710.80 ft, Y 2077.69 ft PI 2 X 4295.19
ft, Y 2573.65 ft or Metric PI 1 X
826.25 m, Y 633.28 m PI 2 X 1309.17 m,
Y 784.45 m A and B control points in terms of
direction must be considered so that the freeway
horizontal alignment is consistent with
alignments outside of the project. Live Demo on
how to design the horizontal alignment through
trial and error efforts
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Freeway Horizontal Alignment
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Ramps Horizontal Alignment Design
A diamond interchange is proposed for the
training project Three below basic elements
should be designed for each ramp Freeway-Ramp
Connector Ramp Alignment Ramp-Local Road
Connector
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Freeway-Ramp Connector Design
Freeway-Ramp Connectors should be designed based
on Figure 504.2a, Figure 504.2b, and Figure
504.2C. Figure 504.2a Advisory standard for
single-lane ramp entrance. Figure 504.2b
Advisory standard for single-lane ramp
exit. Figure 504.2c Advisory standard for ramp
location on a curve
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Single-Lane Ramp Entrance (Figure 504.2A)
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Single-Lane Ramp Entrance (Figure 504.2A)
Discuss control points in the figure and clarify
inlet nose, 2-m and 7-m points When freeway is
not on tangent alignment, select radius to
approximate same degree of convergence. Live
Demo on how to obtain the control points using
Microstation
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Single-Lane Ramp Exit (Figure 504.2B)
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Single-Lane Ramp Exit (Figure 504.2B)
Discuss control points in the figure and clarify
exit nose, 2-m and 7-m points, and DL
distance. Minimum length between exit nose and
end of ramp is 160 m for full stop at end of
ramp Live Demo on how to obtain the control
points using Microstation
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Ramp Location on a Curve (Figure 504.2C)
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Ramp Location on a Curve (Figure 504.2C)
Standards shown in Figure 504.2C are for both
ramp entrances and exits Live Demo on how to
draw the figure in Microstation
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Ramp Alignment Design
Design speed varies along a ramp. Design speed
at the exit nose should be 80 km/h or greater.
Design speed at the inlet node should be
consistent with approach alignment standards, at
least 80 km/h. Design speed at the end of local
road should be 40 km/h Ramp length should be
greater than the stopping sight distance
experienced on the ramp. Appropriate design
speed for any intermediate point on the ramp is
chosen based on its location in relation to the
points of two ends.
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Ramp Widening
When do we need to widen ramps for trucks?
Ramps with curve radii of 90 m or less (outside
ETW) and central angle greater than 60 degrees,
the single lane ramp, and the lane furthest to
the right should be widened in accordance with
Table 504.3A below
Ramp Radius (m) Widening (m) Lane Width (m)
lt40 2.0 5.6 40-44 1.6 5.2 45-54 1.3 4.9
55-64 0.9 4.5 65-74 0.6 4.2 75-90 0.3 3.
9 gt90 0 3.6
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Ramp Length, Lane Drop, 1- or 2-lane Ramps
If the length of a single ramp exceeds 300
meters, an additional lane should be provided on
the ramp to permit passing maneuvers. If
additional lanes are provided near all entrance
ramp intersection, the lane drop should be 2/3 WV
on the right. When design year estimated volume
exceeds 1500 equiv. pc/h, a 2-lane width of ramp
should be provided initially.
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Ramp-Local Road Connector Design
Factors below should be considered Sight
Distance, Left-Turn movements and their storage
requirements, Crossroads gradient at ramp
intersections, Proximity of near-by
intersections A right-angle intersection is
desired to meet the sight distance requirements.
What is the minimum angle allowed? At-grade
intersection design standards should be followed
for the connector design. The ramp intersection
capacity analysis should be conducted before the
signalization is granted and the phasing is
developed.
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Angle of Intersection
Is the design OK?
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Corner Sight Distance
Corner Sight Distance (Table 405.1 Page 400-9)
Design Speed
CSD
40 90 50 110 60 130 70 150
80 170 90 190 100 210 110 230
CSD 0.278 Vmajor 7.5 83.4 meters 90
meters
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Typical Connector Design
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Ramp Setback
Where a separate right turn is provided at ramp
terminals, no free turn due to concerns of
pedestrians. 60 meters should be provided. For
left-turn maneuvers from an off-ramp at an
unsignalized intersection, the length of
crossroads open to view should be
0.278V7.5. Ramp setback from an over-crossing
structure follows Figure 504.3J.
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Ramp Setback (Figure 504.3J)
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Ramp Setback (Figure 504.3J)
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Ram Terminals and Local Intersections
The minimum distance (curb return to curb return)
between ramps intersections and local
intersections should be 125 meters, desirable 160
meters
When intersections are closely spaced., traffic
operations should be applied to examine short
weave and storage lengths and signal phasing.
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Ramp Intersection Capacity Analysis
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Eastbound Off-Ramp Design
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Eastbound On-Ramp Design
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Westbound Off-Ramp Design
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Westbound On-Ramp Design