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# Highway Design Training Course Part II

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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

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

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

Circular Curve in Horizontal Alignment
PI BC EC R

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?

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 Page 200-9 e = 0.09 from Table Page with R = 400 m

Minimum Radius of Circular Curve
Table HDM P200-16 Given emax = 0.10 for freeways (Page 200-9) V = 100 km/h Fs = 0.12 from Page 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

Superelevation Transition
Superelevation Transition should be at the two ends of a curve It consists of crown runoff and superelevation runoff (See Page ) The superelevation runoff has its two third on the tangent and one third on the curve.

Superelevation Transition

Superelevation Transition

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

Superelevation Transition (Solution)
500 m 60 m 400 m B A Curve: emax = 0.10 e = 0.09 given R = 400 m 2/3 Runoff = 0.67 * 99 = m B Curve: emax = 0.10 e = 0.07 Given R = 500 m 2/3 Runoff = 0.67 * 78 = m 100 m < = m No OK, What do we do now?

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)

Stopping Sight Distance on Horizontal Curves

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 McDonald’s 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

SSD on Horizontal Curves (Solution)

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 governs. The Design Speed between successive curves should not more than 15 km/h due to alignment consistency When  < 10°, minimum curve length = 240 m When  < 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

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.

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 > 20 m

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

Horizontal Alignments for Training Project
The Training Project involves the design of five horizontal alignments: One for Freeway Four for Ramps

Freeway Horizontal Alignment Design
Two below PIs are given in the training project for the training project: English PI #1 X = ft, Y = ft PI #2 X = ft, Y = ft or Metric PI #1 X = m, Y = m PI #2 X = m, Y = 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

Freeway Horizontal Alignment

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

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

Single-Lane Ramp Entrance (Figure 504.2A)

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

Single-Lane Ramp Exit (Figure 504.2B)

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

Ramp Location on a Curve (Figure 504.2C)

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

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.

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) < >

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.

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.

Angle of Intersection Is the design OK?

Corner Sight Distance Corner Sight Distance (Table 405.1 Page 400-9)
Design Speed CSD CSD = * Vmajor * 7.5 = 83.4 meters = 90 meters

Typical Connector Design

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 0.278*V*7.5. Ramp setback from an over-crossing structure follows Figure 504.3J.

Ramp Setback (Figure 504.3J)

Ramp Setback (Figure 504.3J)

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.

Ramp Intersection Capacity Analysis

Eastbound Off-Ramp Design

Eastbound On-Ramp Design

Westbound Off-Ramp Design

Westbound On-Ramp Design

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