Study of Three Interchange Designs

See discussions, stats, and author profiles for this publication at: http://www.researchgate.net/publication/273887124
Study of Alternative Design
THESIS · MARCH 2015
DOI: 10.13140/RG.2.1.3839.6963
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Wayne State University
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STUDY OF ALTERNATIVE
DESIGN
Contraflow left, Displaced left, Three-point
Interchanges
Submitted by,
SRIKANT S RAO

College of Engineering
Srikant Rao Page |
srikant.rao@wayne.edu
2
ABSTRACT
Three interchange alternatives were studied to determine their impact on morning
and evening peak hour traffic flow. An interchange is the roadway system where freeways are
connected to either freeway or arterial/local road.
Freeway – Freeway is known as System Interchange
Freeway – Arterial/Local Road is known as Service Interchange
This study is mainly concerned about Service Interchanges. Interchanges are of the diamond
configuration, and interchanges using roundabouts or loop ramps are also popular. Over the
years in United States these interchanges were built and maintained. Interchange helps
reducing conflict points where the pedestrian safety plays key role. Selected interchange has
different conflict points as a matter of fact
Contraflow Left Interchange – 20 Conflict Points
Displaced Left Interchange – 18 Conflict Points
Modified Single Point Interchange – 14 Conflict Points
There are number of measures used to make an interchange safer than it used to be. This
report includes the couple measures for improving safety.
An efficient freeway system will be essential for the growth of any country and
interchanges are important to that efficiency. However, many diamond interchanges have
serious operational problems, interchanges with roundabouts fail at high demand levels, and
loops use lots of expensive land. The study was conducted to find the level of service for the
existing condition. For the above interchanges level of service was found for the present year
(2014 - 2015)

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ACKNOWLEDGEMENT
I heartily want to thank Dr. Joseph E Hummer for giving me this wonderful
opportunity to discover something new about these alternative designs.
I want to thank each and every official from the government agencies and the
private agencies who have supported in a timely manner for this study by
providing the required details to complete my study on those designs
Florida Department of Transportation (Sawgrass Turnpike Enterprise)
Texas Department of Transportation (Victor Vargas)
Crawford, Murphy & Tilly, Inc. (Brian Eads, MO)
Without your help this is nothing but a piece of junk. The data you provided
made this quite decent portion of the report.
Sincerely,
Srikant S Rao

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Table of Contents
Sl. No. Description Pg. No.
Abstract 2
0.1 Introduction 6
0.2 Terminology 6
0.3 Objective 6
0.4 Interchanges for the study 6
0.5 Difference between the designs 7
0.6 Pros & Cons of all 3 designs 7
CHAPTER 1 - Contraflow Left Interchange
1.1 Introduction 8
1.2 Inventory of the design 9
1.3 Typical Roadway Geometry 10
1.4 Design and Operations 10
1.5 Signing and Signboards Diagram 11
1.6 Traffic Signal Control 11
1.7 Applicability 12
1.8 Turning Movement Counts 12
CHAPTER 2 - Displaced Left Interchange
2.1 Introduction 13
CHAPTER 3 - Modified Single Point Interchange
3.1 Introduction 19
CHAPTER 4 - Synchro Analysis
4.1 Analysis Tool 23
4.2 Contraflow Left Interchange Analysis 24
4.3 Displaced Left Interchange Analysis 27
4.4 Modified Single Point Interchange Analysis 30

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Table of Exhibits
# of
Exhibit
Design Description
Pg.
No.
Exhibit 1
CFI
Example 8
Exhibit 2 Inventory 9
Exhibit 3 Typical Roadway Geometry of CFI 10
Exhibit 4 Signing and Signboard Diagram 11
Exhibit 5 NB/EB Daily Traffic 12
Exhibit 6 SB/WB Daily Traffic 12
Exhibit 7
DLT
Inventory in SL-82 at I-35 13
Exhibit 8 Inventory in SL-82 at I-35, Google Maps 14
Exhibit 9 Inventory in SR-80 at I-35, Google Maps 14
Exhibit 10 Typical Design of DLT 15
Exhibit 11 Typical Roadway Geometry of DLT 16
Exhibit 12 Pedestrian Accommodation in DLT 16
Exhibit 14 Peak Hour Volume of I-35 at SR-80 18
Exhibit 15 Peak Hour Volume of I-35 at SL-82 18
Exhibit 16
MSP
Inventory 20
Exhibit 17 Typical Roadway Geometry of MSP 20
Exhibit 19 Annual Average Daily Traffic 22
Exhibit 20 LOS Chart 23
Exhibit 21
CFI
Synchro Model for CFI 24
Exhibit 22 Synchro Model for CFI with Nodes 25
Exhibit 23 Synchro Model for CFI with LOS 26
Exhibit 24
DLT
Synchro Model for DLT 27
Exhibit 25 Synchro Model for DLT with Nodes 28
Exhibit 26 Synchro Model for DLT with LOS 29
Exhibit 27
MSP
Synchro Model for MSP 30
Exhibit 28 Synchro Model for MSP with Nodes 31
Exhibit 29 Synchro Model for MSP with LOS 32
CFI - Contraflow Left Interchange
DLT - Displaced Left Interchange
MSP - Modified Single Point Interchange

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0.1. Introduction
In any road transportation system, an interchange is a road connection that normally
uses grade separation, by providing one or more ramps to permit the traffic on at least one
highway to get through the junction without crossing any other traffic stream. It differs from a
standard intersection, at which roads cross at grade. Interchanges are almost always used
when at least one of the roads is a controlled-access highway known as freeway or a limited-
access divided highway known as expressway, though they may occasionally be used at
junctions between two surface streets (Wikipedia)
0.2. Terminology
1. A freeway or highway interchange is a type of road linkup, linking one highway to
another; to other roads; or sometimes to just a motorway service station. In the U.S.,
interchanges are either numbered according to cardinal interchange number, or by
mileage (typically the latter in most states).
2. A highway ramp (as in exit ramp / off-ramp and entrance ramp / on-ramp) (North
American usage) or slip road is a short section of road, which allows vehicles to enter
or exit a controlled-access highway (freeway).
3. A directional ramp always tends toward the desired direction of travel. This means
that a ramp that makes a left turn exits from the left side of the roadway (a left exit).
Left directional ramps are relatively uncommon as the left lane is usually reserved for
high-speed through traffic. Ramps for a right turn are almost always right directional
ramps. Where traffic drives on the left, these cases are reversed.
0.3. Objective
The interchanges are very massive in usage all over United States implemented after
careful study of the location and reviewing the requirements of roadway users (Traffic Volume
and Crashes). This study is to know about the pros and cons of these Interchanges and what
will be the measure undertaken to mitigate the problem of delay/crashes and finding out
better design for implementing.
0.4. Interchanges considered for this study
In United States there are lot of Interchanges, let me put that up in a common
language that is connecting freeway to freeway/arterial/local road wherein intersection
basically connecting local road to arterial. As US Department of Transportation encouraging
every state to implement new designs, State Department of Transportation professionals are
coming up with designs, which help in reducing delay and increasing safety.
Below is the list of the interchanges considered for this study. Study is mainly based
on these types of interchanges.
 Contraflow left interchange (Modified TUDI)
 Displaced left turn interchange (Continuous flow interchange)
 Three-point interchange (Modified single point interchange)
The study is reporting the safety aspects of all three designs for implementing. It is important
because of the crashes occurring in new designs lately. Although there will be direction
installed why crashes are happening. Nearly 35% of the crashes happening because of this
factor mentioned above. 6 out of 10 pedestrians are the victims for this kind of crashes. To
reduce this kind of crashes we need to
 Educate drivers
 Install legible signs

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0.5. Differentiating mentioned designs:
Factors
Influencing
Contraflow Left
Interchange
Displaced Left Turn
Interchange
Modified Single
Point
Interchange
Where’s
design located
One in State of
Florida, State
Route 869 at
Lyons Rd,
Coconut Creek,
Sunrise, FL
2 in State of Texas, city of San
Marcos One in State of
Missouri, I-55 at
State Route 141,
Arnold, MO
I-35 at Aquarina Springs Drive
&
I-35 at State Route 80
Where’s
design
applicable
Both for freeways
and arterials
Both for freeways and arterials Freeways only
# Of
Pedestrian
Conflict Points
20 Conflict Points 18 Conflict Points 14 Conflict Points
Width of
bridge size
6 Lanes 6 Lanes 4 Lanes, 2 Ramps
Traffic control
used
2 at 3 Phase
Signal
4 at 2 Phase Signal 3 at 2 Phase Signal
Phase addition
for frontage
road
No No Yes
Analysis tool
used
Synchro Studio 8 Synchro Studio 8 Synchro Studio 8
Where the
design can be
implemented
Low to moderate left-turn volumes from the off-ramp to the arterial.
Heavy and balanced through volumes on the
arterial roadway.
Moderate to heavy left-turn volumes from the
arterial to the on-ramp.
0.6. Pros and Cons of these designs:
Design
CONTRAFLOW LEFT
INTERCHANGE
DISPLACED LEFT
INTERCHANGE
MODIFIED SINGLE POINT
INTERCHANGE
Pros
Low critical sum Low critical sums Low critical sums
-
Offers benefit over conventional
diamond
Compact along arterial
- - Signal phasing
Cons
Wide bridge
Pedestrians must cross free flow
ramps
Large bridge
- Wide bridge -

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CHAPTER 1
CONTRAFLOW LEFT INTERCHANGE
1.1. Introduction:
A contraflow left interchange is also known as Modified Tight Urban Diamond Interchange.
Cross Street left turns crossover opposing left turn movements in storage bays prior to the
first ramp intersection. Vehicles move into contraflow lanes within the interchange, before
making the turn onto the ramp. These special lanes run in the opposite direction from the
adjacent thru-lanes, and provide additional storage for left turn vehicles. (Exhibit 1)
Exhibit 1 – Example of contraflow left interchange design
Source: Wikipedia
Diagram showing a glimpse of how does this (Contraflow Left Interchange) design
look like and it’s not typical overview of the interchange.

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1.2. Inventory of the Design:
First state in United States to introduce this new design and was implemented in 1960s
at the intersection of RT 7 with US 441 in Sunrise, Florida. The design replaced a Tight
Diamond interchange that was failing due to the number of signal phases. A narrow overpass
and business development tight to the arterial right-of-way prohibited the possibility of
adding adequate opposing left-turn bays at the interchange approaches. Therefore the
contraflow lanes, which are built within the intersection, were introduced. Originally the
design was to be an interim solution until funds were made available to reconstruct the
interchange. However, the design worked well for nearly 20 years until the bridge was
rebuilt in the 1980s. Today, there are at least two other known CFL interchanges still in
operation in Florida, one of which was originally constructed as a CFL. Lyon Creek Parkway
underneath Florida State Route 869 switching the left turn lanes on the cross streets each other
and bringing the long left turn phases from the single point urban interchange to the TUDI at
26.301177°N 80.186479°W. (The co-ordinates directs to the picture below in Google maps)
Exhibit 2 – Contraflow Left Interchange existence
Source: Google Maps: Located on Lyons Rd and State Route 869, Florida.

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1.3. Typical Roadway Geometry:
Exhibit 3 – Typical Roadway Geometry of Contraflow Left Interchange
Source: Unconventional Arterial Intersection Design by Gitbooks
 The arterial/local road having 2 through lane, 1 left lane (depends on volume) and 1
right lane before the bridge.
 Those 2 thru lanes continue on the bridge, which should be typical.
 Two medians on the arterial one is 12-20ft wide (before the bridge), which separates
left from through and right lanes. Another is three 4ft wide to separate the oncoming
through from left lane and also from the same direction thru movement as in Exhibit 3
 Ramps having minimum of 2 lanes one for right, one for thru & left shared turning
movements.
 Providing signal on either side of the bridge, which is 3-phase. Install all the
mentioned requirements like signage and sign boards for the design as shown in
Exhibit 4
1.4. Design and Operations:
 The CFL design is a disparity on the Diamond interchange, and is best used as an
alternative to a Standard Diamond interchange.
 All movements in a CFL interchange are the same as those of a typical Diamond
interchange configuration except for left turns from the cross street. Cross street left
turns move over into left turn storage lanes (separated from the cross street through
lanes by raised median) approximately 300 feet prior to the first ramp intersection.
 Vehicles precede the first signal and into contraflow lanes within the interchange,
before making the turn onto the ramp. These lanes run in the opposite direction from

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the adjacent through-lanes, and overlap within the interchange. (Ref. UAID)
 The CFL design reduces the number of signal phases compared to a Tight Diamond
interchange from four to three by allowing the two opposing left-turn movements to
be made during the same signal phase.
 The same requirements for additional intersection clearance time exist in the CFL
design as with both SPUI and Standard Diamond interchange designs.
 The greatest design benefit of the CFL is in the extra capacity from the left turn
vehicles being able to move during two phase instead of one.
1.5. Signing and Signboards Diagram:
Exhibit 4 – Signing and Signboard Diagram
Picture Source: Unconventional Arterial Intersection Design (Referred Google Earth street view for Signs)
This portion of the design is very important to keep the safety aspect on top. New
designs keep on coming where the major factor, which affects safety, is driver’s confusion. It
plays a vital role while thinking about safety. This is to educate drivers by installing signing
and sign boards.
Above picture shows the red dot explaining left exit. It doesn’t mean it’s an exit from a
freeway. Tried finding the signboard, but couldn’t find the right signboard used in Florida
that tells left exit only.
1.6. Traffic Signal Control:
A contraflow left interchange basically has traffic signals at each of the two ramp
intersections. Signal control at each of these four junctions operate with just two phases which
are co ordinated with the subsequent signal connecting entry ramps and opposing thru traffic
having 3 phases for the alternative conflicting movements and are coordinated to maintain
progression on the arterial road.

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1.7. Applicability:
The contraflow left interchange design should be taken into consideration for the location
where it has some reflecting factors below,
 Heavy and balanced through volumes on the arterial roadway.
 Moderate to heavy left-turn volumes from the arterial to the on-ramp.
 Low to moderate left-turn volumes from the off-ramp to the arterial.
 Limited bridge deck width, but right-of-way is available on the bridge approaches.
1.8. Turning Movement Counts:
Exhibit 5 – NB/EB daily turning count
Enterprise Turnpike System
Segment Sawgrass Expressway
Facility SR869 Lyons Rd NB off
FLDOT
Northbound/Eastbound
Non Sun Pass Sun Pass Directional
Total50S Toll Type Total 50S Toll Type Total
Total 14039 14039 111473 111473 125512
Average Daily 453 453 3596 3596 4049
Exhibit 6 – SB/WB daily turning count
Enterprise Turnpike System
Segment Sawgrass Expressway
Facility SR869 Lyons Rd SB on
FLDOT
Southbound/Westbound
Non Sun Pass Sun Pass Directional
Total60S Toll Type Total 60S Toll Type Total
Total 15523 15523 124206 124206 139729
Average Daily 501 501 4007 4007 4507
Source: Florida Department of Transportation

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CHAPTER 2
Displaced Left Interchanges
2.1. Introduction:
The DLT interchange, also known as the continuous flow interchange, is an innovative
interchange design that has several aspects similar to the at-grade DLT intersection and some
aspects similar to the DCD interchange. At the time of this report, no known implementations
of this treatment could be identified. Moreover, there was no patent on the DLT interchange
design. Nevertheless, it is a design treatment that has been advocated as promising because
it removes the conflict at the main intersection between left turning and opposing through
vehicles.
The main feature of the DLT interchange design is the left-turn crossovers that are
present on the cross street approaches. In a DLT intersection, the left-turning traffic is
relocated at a location several hundred feet upstream of the first signal-controlled ramp
terminal of the diamond interchange. This left-turning traffic is crossed over the opposing
through lanes. This traffic then travels on a new roadway that is situated between the
opposing through lanes and a roadway and that carries the right-turning traffic from the ramp.
These drivers then make the left turn onto the ramp. (FHWA - AIIR)
2.2. Inventory of the Design:
TxDOT, in partnership with the city of San Marcos, has made intersection improvements to
1. SH 80 (Hopkins Street) at I-35, San Marcos, TX
2. Loop 82 (Aquarena Springs Drive) at I-35 in San Marcos to improve operations at
these intersections.
One is a single-leg CFI at the intersection of State Highway Loop 82 (Aquarena Springs Drive),
Interstate 35's southbound frontage road and I-35's southbound-to-northbound Texas U-turn
(29.893048°N 97.913367°W)Construction completed in the month of May, 2014.
Exhibit 7 – Displaced Left Interchange (1 legged)
Located in Aquarina Spring Dr at I-35, San Marcos, TX

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Exhibit 8 – 1-Legged CFI
Source: Google Maps, Aquarina Springs Dr at I-35, San Marcos, TX
The satellite view of Exhibit 6 is not updated in Google maps because this construction has
finished recently in May 2014. Google maps satellite view was last updated in 2013.
The other, a two-leg CFI, is at the intersection of State Highway 80 (Hopkins Street), I-35's
frontage roads and I-35's Texas U-turns (29.882639°N 97.921915°W). The estimated cost for
both CFIs is $4.7 million.
Exhibit 9 – 2-Legged Continuous Flow Interchange
Source: Google Maps located on SR-80 at I-35, San Marcos, TX
 The DLT interchange is a new interchange design that has similarities to both at-grade
DLT intersection and the double crossover diamond (DCD) interchange.
 The main feature of the DLT interchange is that left-turning traffic crosses over the
opposing through lanes several hundred feet upstream of the main intersection and
then proceeds on a new roadway situated between the opposing through lanes and a
roadway that carries right-turning traffic from the ramp.
 From this new roadway, the left-turn traffic completes its maneuver onto the on-ramp.
 A DLT interchange has four signalized junctions: two at the crossovers for the DLT
movements and two at the ramp terminals of the interchange.
 The DLT interchange design reduces the number of phases at the signal-controlled
ramp terminals within the interchange from three to two, thereby reducing delays to
drivers, pedestrians, and bicyclists as they pass through the interchange area.
 To ensure the smooth progression of traffic, all four signalized junctions are operated

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in a coordinated system.
 A DLT interchange has the same number of conflict points as a conventional diamond
interchange. However, fewer angle crashes may be anticipated in a DLT interchange
compared with a conventional interchange because conflicts are more separated.
(AIIR – FHWA)
Exhibit – 10 - Typical Design of Displaced Left Interchange
Source: FHWA
The primary design elements of a DLT interchange (Exhibit 11) are as follows:
• Left-turning traffic is displaced from the main intersection by adding lanes that allow traffic
to cross the opposing through traffic at a signal-controlled location 400 to 500 ft upstream of
the main intersection.
• Radii of the crossover movements range from 150 to 200 ft, and radii of the left-turning
movement at the interchange nodes depend on the turning path of the selected design
vehicle (Exhibit 11).
• A larger overall interchange footprint may be needed, given that major road left-turning
vehicles travel on the opposite side of the roadway, requiring a wider median.
• U-turn movements on the arterial roads are prohibited in the interchange area, similar to
the DLT intersection.
• Access to adjacent properties is limited by the interchange design, and accommodation of
individual driveways is considered on a case-by-case basis.
• Pedestrians can be accommodated in a DLT interchange as shown in Exhibit 12. (AIIR –
FHWA)

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Exhibit 11 - Typical Roadway Geometry
Source : FHWA
Exhibit 12 – Pedestrian Accommodation
Source : FHWA
A DLT interchange typically has traffic signals at each of the two left-turn crossovers and at
each of the two ramp intersections. Signal control at each of these four junctions operate with
just two phases for the alternative conflicting movements and are coordinated to maintain
progression on the arterial road. Traffic signals at a DLT interchange are fully actuated to
minimize delay. (AIIR – FHWA)
2.6. Applicability:
The DLT Interchange design should be taken into consideration where it is reflecting
the same factors below, (AIIR – FHWA)
 Limited bridge deck width, but right-of-way is available on the bridge approaches.
 Low to moderate left-turn volumes from the off-ramp to the arterial.

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2.7. Signing and Signboard Diagram:
Exhibit 13 – Displaced Left Turn at SR-80 & I-35, San Marcos, TX
Source: Victor Vargas (TxDOT)

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2.8. Turning Movement Counts:
Exhibit 14 – Peak hour volume of I-35 at SR-80
Exhibit 15 – Peak hour volume of I-35 at Aquarina Springs Drive (SL-82)
Source: Victor Vargas (TxDOT)

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CHAPTER 3
MODIFIED SINGLE POINT INTERCHANGE
3.1. Introduction:
Modifying a single-point interchange is not a standard design and is not
discussed in most published literature on interchange design. This could be because most of
this literature does not deal with large skew angles. As quoted earlier, the AASHTO design
guide only states that “extreme care” should be used when designing single-point
interchanges with a skew greater than 30 degrees. This site has a skew nearly double that
threshold. The AASHTO design guide does not provide any additional guidance in the design
of interchanges with such a severe skew.
The modified single-point interchange design takes advantage of the skew to provide
smooth left turn movements at the interchange. The off-ramp lefts are brought together at the
middle of the bridge and controlled by one signal similar to the single-point. Because of the
skew, these approaches meet the arterial at about a 15-degree offset. These approaches do
not require the large clearance distance and time that are associated with the traditional
single-point interchange movements. The on-ramp left turn movement geometrics are similar
to the diamond interchange. Each of the on-ramp left turn movements is controlled by
separate signals. A nonstandard bridge design is required. This bridge is similar to the
single-point interchange, but smaller because only two ramps meet at the bridge, which do
not require a larger bridge deck for support. This design is similar to the diamond
interchange in that the on-ramp left turns occurs at either end of the interchange. Through
traffic on the arterial can be stopped by up to two signals, with the third signal giving
continuous green for the through movement. The design is comparable to the single-point
interchange because the off-ramp lefts are brought together at the middle of the interchange.
The main operational characteristic, which is unique the modified single-point design, is that
each of the three signals has two phases and the signals are spaced far enough apart to allow
adequate storage between the signals.

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3.2. Inventory of the design:
Missouri is the first state to introduce and implement this design for the first time. This
design is constructed one in the state of Missouri that is on MO-141 at I-55, Arnold, MO.
Crawford, Murphy & Tilly, Inc. a consulting company took over this project to find the right
alternative for the area where there was a serious problem of crashes and intersection delay.
The below design was the best of the alternatives they found.
Exhibit 16 – Location of the design
Source: Google Maps, located on MO-141 at I-55, MO
Exhibit 17 – Modified Single Point Interchange
Source: AutoCAD self-designed (Not to Scale)

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 12ft of lane width used on both arterials and freeway
 10-11ft on all side of ramps
 2 phase signal on all 3 signal location
 Centre median could be minimum of 4ft wide
 Median near the ramps could be 12-20ft wide
 Install the signboards as below
Design is found in exhibit 17 part of the design. This design have 2 kind of ramps, one
is Directional ramps (NB/SB or WB/EB) another is center ramps with left turn lanes which has
moderate to heavy left turns from freeway to arterial. All directional through movements are
coordinated with the consecutive signals ahead of them.
3.5. Signing and Signboard Diagram:
Exhibit 18 – Signing and pavement marking diagram
Source: Self-designed using Google Earth Street View
A modified single point interchange typically has traffic signals on 3 sides where 2 on either
side of the bridge where the ramps connect to the arterial/local road and 1 at the center
where 2 directional thru movement and 2 directional left ramps connecting arterial. Signal
control at three junctions operates with just two phases for the alternative conflicting
movements and are coordinated to maintain progression on the arterial road.
3.7. Applicability:
The modified single point interchange design should be taken into consideration where it is
reflecting the same factors below,

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 Moderate to heavy left-turn volumes from the off-ramp to the arterial.
3.8. Turning Movement Counts
Exhibit 19 – Annual Average Daily Traffic Volume
Source: Crawford, Murphy & Tilly, Inc., MO
Turning Movement Count Summary - MO 141 and I-55 Southbound Ramps
Typical Weekday
Hour Southbound Westbound Northbound Eastbound Total
Beginning Left Through Right Left Through Right Left Through Right Left Through Right Volume
TOTAL 0 13,723 7,357 0 0 0 4,689 13,561 0 0 0 0 39,330
Turning Movement Count Summary - MO 141 and I-55 Southbound Ramps
Typical Saturday
TOTAL 0 13,530 7,110 0 0 0 5,912 12,978 0 0 0 0 39,530
Turning Movement Count Summary - MO 141 and I-55 Center Ramp
Typical Weekday
TOTAL 0 13,242 0 7,273 0 8,282 0 10,637 0 7,151 0 6,112 52,697
Turning Movement Count Summary - MO 141 and I-55 Center Ramp
Typical Saturday
TOTAL 0 13,098 0 6,435 0 6,874 0 12,250 0 6,128 0 7,677 52,462
Turning Movement Count Summary - MO 141 and I-55 Northbound Ramps
Typical Weekday
TOTAL 7,131 13,882 0 0 0 0 0 10,878 6,164 0 0 0 38,055
Turning Movement Count Summary - MO 141 and I-55 Northbound Ramps
Typical Saturday
TOTAL 6,085 13,889 0 0 0 0 0 12,455 5,945 0 0 0 38,374

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CHAPTER 4
SYNCHRO ANALYSIS
4.1. Analysis Tool:
Considered using Synchro 8. Synchro Studio is robust, easy-to-use traffic signal
software that helps traffic engineers and transportation planners design, model, optimize,
simulate, and animate signalized and un-signalized intersections (including roundabouts),
delivered in a comprehensive, standardized file format.
Synchro 8 is a suitable tool to find out the intersection delay, level of service of an
intersection, intersection splits and offsets because for VISSIM we need to have the exact
signal timing to run the model, wherein synchro we don’t need to worry about the signal
timings as it gives by itself. Below are the exhibits to show how the interchanges were
designed in sychro model
Main aim of using this software is to find out the level of service at the intersections. If
it is worse, trying to find better way to improve the intersections which is cost beneficial.
Below attached is the chart for finding the level of service with the help of intersection delay
in seconds per vehicle.
Exhibit 20 – LOS Chart
Source: Wikipedia

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4.2. Contraflow Left Interchange Analysis:
Exhibit 21 – Synchro Model for Contraflow left Interchange
Source: Trafficware Synchro 8 – Self Designed (Not to Scale)
This interchange took lot of time to complete because of lot of errors occurred while
going through the design. I worked on all of the factors, where the errors were popping up
when I checked code of the design application. Initially encountered more than 20 errors and
10 warnings. Now there is no single error in the model and some warnings are still present
but it’s not a serious issue, which affect the results. Design consists of 4 - 2Φ signal and 2 - 3Φ
signal on either side of the bridge. The analysis was carried out for the volume data (Courtesy
of Florida Department of Transportation). Detailed report of synchro analysis is attached in
the appendix part of the report.

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Below attached exhibit explains the number of nodes and intersections used in the design for
modeling purposes.
Exhibit 22 – Contraflow Left Interchange with # of nodes
As you can see the exhibit above having number of nodes present in the design
where the number with white boxes say those are signalized intersection and the numbers
with blue boxes say those are nodes where 2 roads connect making an angle except node 25
and 29 are un-signalized intersection with yield sign.

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Below exhibit shows the contraflow left design with the level of service on all intersections.
Exhibit 23 – Contraflow Left Interchange with LOS
Source: Synchro 8 (Self-designed - Not to Scale) (Volume data - Courtesy of FLDOT (Sawgrass Turnpike Enterprise))
As the volume data provided by Florida department of transportation mentioned
above. Those data were implemented for the existing condition. The Level-of-service turned
out to be like as in the exhibit above. The nodes with level of service U refer to a node or un-
signalized intersection. (Yield Sign, Stop Sign, Free)
Methodology:
 After designing this model above shown in exhibit 23 in synchro. The volumes are
entered provided by Florida department of transportation (Sawgrass Turnpike
Enterprise).
 The volume were provided for vehicles passing the in and out of the tollgates. Both on
ramps have tollgates installed. Volume data were divided into toll passed vehicles
and toll not passed vehicles.
 By the evaluating engineering consideration I assumed the numbers for the turning
counts.
 Initially I found the level of service to be F on 4 intersections in the middle. Later I
played with the intersection cycle length to make it D.
 Tweaked the Signal timings a bit which helped me to achieve level of service B on all
those 4 intersections in the middle. This is the least possible way to make an
improvement

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4.3. Displaced Left Interchange Analysis:
The design was pretty tough compared to the contraflow and modified single point
because of the displaced left as we can see in exhibit 22. There was lot of errors and warnings
in this design as well, still there are warnings, which does not affect the result part of the
design but no errors in code check.
Exhibit 24 – Synchro Model for Displaced Left Interchange
This interchange took lot of time to complete because of weaving part in the design as
shown in the above figure. There are 2 - 2Φ and 2 - 1Φ signal on either side of the bridge. On
the bridge it should be 4 – 2Φ here there are 6 that’s because of the limitations of synchro. The
minimum distance between the intersections should be maintained 100ft. The analysis was
carried out for the volume data provided (Courtesy of Victor Vargas, Texas Department of
Transportation). Detailed report of synchro analysis is attached in the appendix part of the
report.

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Below is the exhibit showing the design with number of nodes on it.
Exhibit 25 – Displaced Left Interchange with # of nodes
As mentioned above the numbers with white boxes are the signalized interchanges.
Numbers with blue boxes are nodes (lines connected each other with an angle). Except the
nodes 23, 15, 21 & 42 are un-signalized intersection with yield signs.

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Below design shows the level of service on the intersections.
Exhibit 26 – Displaced Left Interchange with LOS
Source: Synchro 8 (Self-designed - Not to Scale) (Volume data - Courtesy of Victor Vargas, TxDOT)
As per the data provided by TxDOT the volumes were inputted and the results are as
shown in exhibit 24. Level of service U refers to an un-signalized intersection where yield
sign, stop signs are used.
Methodology:
 Lengths were measured off of the existing design in San Marcos, TX. Using those
lengths this design was modeled.
 Then have the volume data entered, courtesy of Victor Vargas, TxDOT. Implemented
to the design.
 Initially the level of service was different for every intersection. Then for the errors
and warnings of coding and fixed all those errors, then LOS dropped down to C.
 After making some alterations for intersection cycle lengths and intersection offsets,
simulation process started working fine without any errors
 By tweaking the signal timings it helped me to achieve the Level of Service at least B.
There was nothing I could possibly make it A. When I was trying to make level of
service A, every other intersection was getting altered.
 One intersection has level of service B in exhibit 26. I tried making it A in many
possible ways but because of the SB thru and WB thru volumes it couldn’t be possible
to attain level of service A for that intersection.

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4.4. Modified Single Point Interchange Analysis:
The interchange in the attached exhibit 25 is also known as Three-point interchange.
Compared to other 2 designs above this design was pretty easy because of the SPUI design
already present in the sample designs in Trafficware.
Exhibit 27 – Synchro Model for Modified Single Point Interchange
It is the altered design of Single Point Urban Interchange (SPUI). There are 3 - 2Φ
signal. I tried providing 100% green for NB and SB thru, but the design simulation turns
unusual. The analysis was conducted for the volume data provided (Courtesy of Crawford
Murphy & Tilly Inc., MO). Detailed report of synchro analysis is attached in the appendix part
of the report.

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Below is the exhibit showing the number of nodes present in the design.
Exhibit 28 – Modified Single Point Interchange with # of nodes
As I mentioned above the numbers with white boxes are the signalized intersections.
Numbers with blue boxes are nodes (line connecting each other with an angle).

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Below exhibit showing the modified single point interchange with the level of service wherein
the volume data were inputted.
Exhibit 29 – Modified Single Point Interchange with LOS
Source: Synchro 8 (Self-designed - Not to Scale) (Volume data - Courtesy of Crawford, Murphy & Tilly, MO)
The 3 intersections with level of service A is doing very well and the locations with
level of service U refers to the node, that is ramps and freeway connecting at that point.
Methodology:
 First of all I mentioned this design was altered Single point urban interchange, only
modification from single point is that there are just 2 center ramps in this design as in
the Exhibit 29.
 Took the length of the arterial in the existing design of MO-141 at I-55, Arnold, MO.
Implemented those lengths to the synchro model to achieve following intersections in
both Northbound and Southbound.
 Then comes the volume data for the model, as by the courtesy of Crawford, Murphy &
Tilly, MO. Volumes were entered.
 The level of service for all three intersections was initially C, then I optimized the
intersection cycle lengths and intersection offsets to achieve B.
 Although wasn’t happy with it later I tweaked the signal timings a little which really
helped me to achieve LOS A as Exhibit 29 explains it all.

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Appendix - Table of Contents
Sl. No. Description Pg. No.
1.1 Time space diagram for CFLI 35
1.1.1 Results 37
1.1.2 Conclusions 39
1.2 Time space diagram for DLTI 40
1.2.1 Results 42
1.3 Time space diagram for MSPI 45
1.3.1 Results 46

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Appendix - Table of Exhibits
# of
Exhibit
Design Description
Pg.
No.
Exhibit 30
CFLI
Time space diagram for intersection 1 35
Exhibit 31 Time space diagram for intersection 2 36
Exhibit 34 Intersection summary for intersection 1 37
Exhibit 35 Signal timing for intersection 1 37
Exhibit 42
DLTI
Exhibit 54
MSPI

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Appendix
The part of the report consists of software analysis. This section is concerned about
design recommendations for future implementation. The results are attached to this part of the
report. The report is found with respect to the nodes used in Exhibit 21, 24 & 27 in chapter 4.
Appendix consists of these studies below
 Time space diagram for different intersections
 Results
 Conclusions
Time Space Diagrams for Selected Designs:
1.1. Contraflow Left Interchange: (CFLI)
The intersections are mainly divided into two types one is signalized and other is un-
signalized intersection our focus is on the signalized intersections. This design has 6
intersections, but considering only the main intersections for the exhibits. As shown in above
exhibit 22 the intersections are numbered, following those numbers the time space diagram
will be attached below. The numbers for the intersections mentioned are in the exhibit 22
Exhibit 30 – Time Space Diagram for intersection 1
Source: Self Designed CFLI model (Synchro 8)

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1.1.1. Results:
 Implementing the volume data provided by Florida department of transportation did
simulation.
 The level of service was not that decent. I believe it’s because of the 3-phase signal on
either side of the bridge making the intersection delay higher.
 Simulation was done for various volumes like larger and smaller volumes. I got good
output for the simulation done for the smaller numbers but not the other one.
a. Intersection Summary: Intersection 1
Exhibit 34 – Intersection 1 summary from the synchro report
Source: Synchro 8
b. Signal Timing:
Exhibit 35 – Signal timing for intersection 1
Source: Synchro 8

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Source: Synchro 8
b. Signal Timing:
Source: Synchro 8
Source: Synchro 8
b. Signal Timing:
Source: Synchro 8

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Source: Synchro 8
b. Signal Timing:
Source: Synchro 8
1.1.2. Conclusion:
 As discussed in the introduction part this design has cons more than the pros.
 The negative part of the design is that it is hard to coordinate a 3-phase signal to
improve the progression.
 Eventually if the signals are coordinated, it is a nightmare for the design if there is
moderate to heavy left turn volume from the ramps
 It is suitable for the location where the left turns from the ramps are low to moderate.

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1.2. Displaced Left Turn Interchange: (DLTI)
In this design there are 10 signalized intersections. Attached are only the main
intersections time space diagrams as noted, the number for an intersection is shown in the
exhibits above i.e. exhibit 25.
Exhibit 42 – Time space diagram for intersection 32
Source: Synchro 8
Source: Synchro 8

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Source: Synchro 8
Source: Synchro 8

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42
1.2.1. Results:
 The volume data provided by TxDOT were implemented for the simulation and when
the simulation is done the output was expected.
 Then the variety of different volumes were assumed and entered it worked well with
the smaller numbers, but found really bad level of service for the larger ones.
 Below attached are some summaries of the intersection with signal timings. The
numbers for the intersections were taken from the exhibit 25.
Source: Synchro 8
b. Signal Timing:
Source: Synchro 8
Source: Synchro 8

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b. Signal Timing:
Source: Synchro 8
Source: Synchro 8
b. Signal Timing:
Source: Synchro 8
Source: Synchro 8
b. Signal Timing:
Source: Synchro 8

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1.2.2. Conclusion:
 The limitations of synchro when the intersections are placed very near to one another
it is not counted as an intersection
 Since it has to maintained 100ft. minimum between 2 intersections that makes the
design worse while simulating.
 The design does not entertain moderate to heavy left turns from the ramps. Because of
the problem mentioned above.
 It is perfectly suitable for the design where the ramps left turn has low to moderate
volume.
SPACE INTENTIONALLY LEFT BLANK

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1.3. Modified Single Point Interchange: (MSPI)
There are 3 intersections in a row in this design as shown above in the exhibit 28 the
number with the white boxes are intersections. Time space diagram is prepared for those
three intersections are as follow by the number on it.
Exhibit 54 – Time Space Diagram for intersection 1.
Source: Self Designed MSPI model (Synchro 8)
This is the time space diagram for the intersection that is numbered as 1 in the exhibit 28.
This is the time space diagram for the intersection 2 as shown in the exhibit 28.

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This is the time space diagram for the intersection 9 shown in the exhibit 28.
1.3.1. Results for MSPI:
 The design was simulated for the volume data provided by the agency from Missouri
and also simulated for variety of volume data like larger numbers and smaller
numbers.
 For every volume this design responds better than other 2 designs mentioned above.
 This design is a noble recommendation. After all the data provided is not precise for
larger and smaller numbers but the level of service turned out pretty decent.
 Existing condition level of service is A below attached are the exhibits showing the
intersection summary with the level of service and signal timing.
Source: Synchro 8

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b. Signal Timing:
Source: Synchro 8
Exhibit 59 – Intersection 2 summary from synchro report
Source: Synchro 8
b. Signal Timing:
Source: Synchro 8
Exhibit 61 – Intersection 9 summary from synchro report
Source: Synchro 8
b. Signal Timing:
Exhibit 62 - Signal timing for intersection 9
Source: Synchro 8

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1.3.2. Conclusion:
 When the 3 intersections are coordinated with all the movements achieving level of
service A is very easy.
 In exhibit 29, NB and SB (intersection 2 & intersection 1 respectively) thru movement
should have 100% green.
 If the roads were aligned in a skew angle my recommendation would be this design,
works better with heavy off ramp left turn, moderate to heavy thru and on ramp left
turn on the arterial.
 If the roads cross at 90’, think about the actual dollar value for the construction
because it needs large bridge to carry left turning ramps, which is expensive. But no
loss of implementing this design if it is worth it.
 Over the other 2 designs this design takes 1st
place for the any future consideration.
SPACE INTENTIONALLY LEFT BLANK

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References:
 www.wikipedia.com for some of the terminology referred the website.
 “Alternative Intersection/Interchange Information Report” (AIIR) from Federal
Highway Administration.
 FHWA Publication No.: FHWA-HRT-09-056, Principal Investigators Warren Hughes
and Ram Jagannathan
 “Unconventional Alternative Intersection/Interchange Designs” by GITBOOKS
 “Operational Performance of Urban Interchanges with a Large Skew: A comparison of
Diamond, Single-Point & Modified Single-Point Interchanges” by Brian Eads, MO
 “Alternate Intersection Analysis” by Klotz Associates, Inc. TX for TxDOT
 Google search to find the MUTCD signs for designing Signing and Signboards
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