Traffic Operations and Management: Module1: Grade Separation & Weaving Segments

Traffic Operations &
Management
Lecture Notes
Spring 2021
Dr. Wael ElDessouki
Copyright © 2021
TTE 422 Traffic Operations - Copyright © 2021 Wael ElDessouki
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Grading, Exams..etc*
 Prerequisite:
TTENG 441 Traffic Engineering
 2 Mid-term Exams 40%
 Final Exam 40%
 Extras: Quizzes 2 x 5%+ Projects, HW,.. Etc. 20%
 Textbook:
Roess, R. P., Prassas, E. S., and McShane, W. R., “Traffic Engineering”,
Fourth Edition, Prentice-Hall, 2011.
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Introduction & Review
The objective of this is course is to integrate and apply traffic
engineering and control concepts, to enhance traffic
operations safety and level of service without adding new
infrastructure capacity. Advanced techniques such as traffic
flow theory, shockwave analysis, lane management and, and
intelligent transportation systems will also be addressed.”
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Course Modules
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Module Duration
Module 1: Grade Separation & Interchanges
1. Interchanges Layout
2. Weaving Segment LOS
2 Weeks
Module 2: Roundabouts
1. Geometric Design
2. Capacity Analysis
3. Roundabout Level of Services
3 Weeks
Module 3: Lane Management
1. Management Strategies
Shoulder Lane- HOV Lane - Lane Reversal
2. Assessment for Lane Management Strategies
3 Weeks
Module 4: Traffic Calming
1. Traffic calming strategies
2. Speed hump impact on capacity
2 Weeks
Module 5: Traffic Flow Theory & Shockwave Analysis
1. Car following Model
2. Macroscopic Flow Models
3. Shockwaves Applications
3 Weeks

Important Dates
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Quiz/ Exam Date
Quiz 1 Week of Feb 7
MIDTERM EXAM 1 March 1st
Quiz 2 Week of Mar 21st
MIDTERM EXAM 2 April 5th

Module 1:
Grade
Separation &
Interchanges
TTE 422 Traffic Operations - Copyright © 2021 Wael ElDessouki Spring 2021

A- Grade Separation:
Interchanges Layouts
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Grade Separation & Interchanges
Warrants for Grade Separation:
 In cases where two or more uninterrupted freeway
facilities intersect together.
 In case where an uninterrupted freeway facility
intersects with a regular interrupted facility
(highway, road, collector, ..etc.)
Principles of the Separation Methodology:
 For all movements with a crossing points of conflict,
each movement will have an elevation level such
that all crossing pints of conflicts are eliminated.
 Merging and diverging points are allowed.
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Separation Steps: 1-Through Movements
Through Movements: Typically, each direction will have a
separate elevation.
This will eliminate 12 out of 16 crossing points of conflict.
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Separation Steps: 2-Right Turn Movements
Typically, Right Turn movements will not need grade separation.
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Separation Steps: 3-Left Turn Movement Treatment
There are Three methods for treating the LT movement and
depends on the LT volume.
Method 1: Indirect Left Turn
For low volumes: < 1200 veh/hr
Advantages: Low ROW
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Method 1: Indirect Left Turn Example: Cloverleaf Interchange
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Method 2: Semi-Direct Left Turn (two levels)
For Moderate traffic: 1800-1200 veh/hr
Advantages:
Moderate ROW
Better Capacity & Speed
Disadvantages:
CO$$$T
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Method 2: Semi-direct Left Turn Example: Turbine Interchange
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Method 2: Semi-direct Left Turn Example: Turbine Interchange
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Method 2: Semi-direct Left Turn Example:
Semi-Direct T-Interchange
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Method 3: Direct Left Turn (three levels)
For Moderate traffic: >1800 veh/hr
Advantages:
Better Capacity & Speed
Disadvantages:
CO$$$$$$$$T
Large ROW
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Method 3: Direct Left Turn Example: T – Interchange
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Mixed Configuration Interchanges:
Trumpet Interchange
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Trumpet Interchange
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Roundabout Interchange
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B- Grade Separation:
Weaving Segment LOS
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Weaving Segments
 Weaving Segments can be primarily on Freeways.
 Weaving occurs due to merging and diverging traffic from the
freeway.
 The objective of the HCM2000 methodology for analyzing weaving
segments is to assess LOS.
 Limitations of the HCM2000 Methodology:
i. Special lanes, such as high-occupancy vehicle lanes, in the weaving
segment;
ii. Ramp metering on entrance ramps forming part of the weaving
segment;
iii. Specific operating conditions when oversaturated conditions occur;
iv. Effects of speed limits or enforcement practices on weaving segment
operations;
v. Effects of intelligent transportation system technologies on weaving
segment operations;
vi. Weaving segments on collector-distributor roadways;
vii. Weaving segments on urban streets; and
viii. Multiple weaving segments.
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Weaving Segments: Methodology
The HCM2000 methodology has five distinct
components:
1) Models predicting the space mean speed (average
running speed) of weaving and nonweaving vehicles in
the weaving segment (models are specified for each
configuration type and for unconstrained and
constrained operations);
2) Models describing the proportional use of lanes by
weaving and nonweaving vehicles, used to determine
whether operations are unconstrained or constrained;
3) An algorithm that converts predicted speeds to an
average density within the weaving segment;
4) Definition of level-of-service (LOS) criteria based on
density within the weaving segment; and
5) A model for the determination of the capacity of a
weaving segment.
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LOS Criteria:
The LOS of the weaving segment is determined by comparing the
computed density with the criteria of Exhibit 24-2.
A single LOS is used to characterize total flow in the weaving segment,
although it is recognized that in some situations (particularly in cases of
constrained operations) nonweaving vehicles may achieve higher-
quality operations than weaving vehicles.
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Weaving Segments: Parameters
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A
B

Weaving Segments: Parameters (cont.)
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Step 1: Volume Adjustments:
All of the models and equations in this chapter are based on
peak 15-min flow rates in equivalent passenger cars per hour.
Thus, hourly volumes must be converted to this basis using
Equation 24-1:
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Step 2: Construct a Weaving Segment Diagram as shown:
After volumes have been converted to flow rates, it is useful to
construct a weaving diagram
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Vo1 = 1500 vph
Vw1= 500 vph
Vo2= 400 vph
Vw2= 300 vph
Vw = 800 vph
V = 2700 vph
VR = Vw/V
VR = 800/2700= 0.296

Step 3: Determine Weaving Segment Configuration:
 Weaving segment configuration depends on the minimum number of lane changes needed by
each weaving movement
 Type A: Weaving vehicles in both directions must make one lane change to successfully complete
a weaving maneuver.
 Type B: Weaving vehicles in one direction may complete a weaving maneuver without making a
lane change, whereas other vehicles in the weaving segment must make one lane change to
successfully complete a weaving maneuver.
 Type C: Weaving vehicles in one direction may complete a weaving maneuver without making a
lane change, whereas other vehicles in the weaving segment must make two or more lane
changes to successfully complete a weaving maneuver.
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Step 3: Determine Weaving Segment Configuration: Examples
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Step 4: Determine Weaving & Non-Weaving Speeds:
The algorithm for predicting the average speed for weaving and
non weaving may be stated as following:
Assuming the Smin = 24 km/hr and Smax = the Free Flow Speed (SFF),
then:
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Step 4: Determine Weaving & Non-Weaving Speeds(cont.):
Initial estimates of speed are always based on the assumption of
unconstrained operation. This assumption is later tested, and
speeds are recomputed if operations turn out to be constrained.
The combination of Equations 24-2 and 24-3 yields sensitivities that
are consistent with observed operations of weaving segments.
As the length of the weaving segment increases, speeds also
increase, and the intensity of lane changing declines.
As the proportion of weaving vehicles in total flow (VR) increases,
speeds decrease, reflecting the increased turbulence caused by
higher proportions of weaving vehicles in the traffic stream.
As average total flow per lane (v/N) increases, speeds decrease,
reflecting more intense demand.
Constrained operations yield lower weaving speeds and higher
nonweaving speeds than unconstrained operations. This reflects
the fact that weaving vehicles are constrained to less space than
equilibrium would require, whereas nonweaving vehicles have
correspondingly more than their equilibrium share of space.
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Step 4: Determine Weaving & Non-Weaving Speeds (cont.):
Weaving Intensity Factor:
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Vo1 = 1500 vph
Vw1= 500 vph
Vo2= 400 vph
Vw2= 300 vph
Vw = 800 vph
V = 2700 vph
VR = Vw/V
VR = 800/2700= 0.296
L= 250 m
N = 5 lanes
Sff = 90 kph
Ww = [0.15 (1 +0.296)^2.2 *(2700/5)^0.97] / [3.28 * 250 ]^0.8 = 0.55359
Wnw = [0.0035 (1 +0.296)^4.0* (2700/5)^1.3] / [3.28 * 250 ]^0.75 = 0.229
Ww = 0.55389 *.35/.15 = 1.292
Wnw = 0.229 * 20/35 = 0.13
Sw = 24 + (90-16)/(1+0.55359) = 71.63 kph
Snw = 24 + (90-16)/(1+0.229) = 84.22 kph
Nw = 1.21 *5 * 0.296^.571 * 250^0.234 /(71.63)^0.438 = 1.69 > 1.4
Sw= 24 + 74/2.292 = 42.75 kph
Snw =24 +74 /1.13 = 86.73 kph

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Step 6: Determine Type of Operation:
The determination of whether a particular weaving segment is
operating in an unconstrained or constrained state is based on the
comparison of two variables :
Nw = number of lanes that must be used by weaving vehicles to
achieve equilibrium or unconstrained operation, and
Nw(max) = maximum number of lanes that can be used by weaving
vehicles for a given configuration.
Fractional values for lane use requirements of weaving vehicles may
occur because weaving and nonweaving vehicles share some lanes.
Cases for which Nw < Nw(max) are unconstrained because there are
no impediments to weaving vehicles using the number of lanes
required for equilibrium.
If Nw > Nw(max), weaving vehicles are constrained to using Nw(max)
lanes and therefore cannot occupy as much of the roadway as
would be needed to establish equilibrium operations.
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Step 6: Determine Type of Operation (cont.):
If Constrained: Then Go to Step 5 and recalculate Speeds using
the weaving intensity factors for constrained operations
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Step 7: DETERMINING WEAVING SEGMENT SPEED :
After calculating the speeds in the segment for
weaving and weaving vehicles, then the average
speed in the segment is estimated as following:
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Step 7: DETERMINING WEAVING SEGMENT SPEED :
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Sw= 24 + 74/2.292 = 42.75 kph
Snw =24 +74 /1.13 = 86.73 kph
S = 2700 / [(800/42.75) + (1900/86.73)) = 66.5 kph
D = (2700/5)/66.5 = 8.12 pc/ln/km  LOS = B
Vo1 = 1500 vph
Vw1= 500 vph
Vo2= 400 vph
Vw2= 300 vph
Vw = 800 vph
V = 2700 vph
VR = Vw/V
VR = 800/2700= 0.296
L= 250 m
N = 5 lanes
Sff = 90 kph

Step 8: DETERMINING DENSITY & LOS:
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End of Module 1
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Traffic Operations and Management: Module1: Grade Separation & Weaving Segments

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Traffic Operations and Management: Module1: Grade Separation & Weaving Segments