Comparison of Single Point Urban Interchange and Diverging

Home , Cloverleaf interchange, Diamond interchange

COMPARISON OF SINGLE POINT URBAN INTERCHANGE AND DIVERGING

DIAMOND INTERCHANGE THROUGH SIMULATION

Thesis

Submitted to

The School of Engineering of the

UNIVERSITY OF DAYTON

In Partial Fulfillment of the Requirements for

The Degree of

Master of Science in Civil Engineering

Rawan Ramadhan

Dayton, Ohio

May 2019

COMPARISON OF SINGLE POINT URBAN INTERCHANGE AND DIVERGING

DIAMOND INTERCHANGE THROUGH SIMULATION

Name: Ramadhan, Rawan

APPROVED BY:

______Deogratias Eustace, Ph.D., P.E., PTOE Philip Appiah-Kubi, Ph.D. Advisory Committee Chairperson, Committee Member, Associate Professor, Associate Professor, Department of Civil and Environmental Department of Engineering Engineering and Engineering Mechanics Management, Systems, and Technology

______Paul Goodhue, P.E., PTOE Committee Member, Traffic Key Services Leader, LJB, Inc.

______Robert J. Wilkens, Ph.D., P.E. Eddy M. Rojas, Ph.D., M.A., P.E. Associate Dean for Research & Innovation Dean, School of Engineering Professor School of Engineering

Rawan Ramadhan

2019

iii

ABSTRACT

COMPARISON OF SINGLE POINT URBAN INTERCHANGE AND DIVERGING

DIAMOND INTERCHANGE THROUGH SIMULATION

Name: Ramadhan, Rawan University of Dayton

Advisor: Dr. Deogratias, Eustace

In 1960, there were 74,431,800 vehicles registered in the United States. Looking at the most recent data currently available shows that in 2016 there were 268,799,083 registered vehicles in the United States. Roadway facilities constructed in the 1960s were not designed to handle vehicular traffic of these proportions. The ever increasing volumes of motor vehicle traffic at heavily traveled interchanges and intersections heighten the risk of single or multiple vehicle crashes particularly when they are not designed to manage high volumes. Traffic engineers from state and federal departments of transportation have responded to calls for safer roads and interchanges in some areas that have been identified as dangerous because of an increase in fatal and non-fatal motor vehicle crashes. In the road network the highway system and the local street system are related. According to the

Federal Highway Administration, “the term interchange means the junction of two or more streets requiring partial or complete grade separation.” Interchanges located in urban areas are utilized to facilitate traffic flow between arterial roadways and freeways on- and off- ramps. Congestion and safety are the two main objectives traffic engineers consider while remodeling an interchange design. Several types of renovated interchanges are normally considered to meet the growing population mobility needs. The Single Point Urban

Interchange (SPUI) is one of the solutions has been considered since 1974 but it was

iv flourished and implemented in the 1990s. The other innovative interchange solution appeared first in France in the mid-1970s known as Diverging Diamond Interchange (DDI).

Likewise, the DDIs did not gain popularity back then until in the 2000s. The first DDI in the United States was constructed in 2009 in Springfield, Missouri.

The main aim of this study is to compare the performance of traffic flow between

SPUI and DDI based on existing traffic data for a peak hour retrofitting an existing

Conventional Diamond Interchange (CDI). The analysis of the two interchange designs in conjunction with the existing design are used in the comparison study to identify which interchange design performs best among each other. The Measures of Effectiveness

(MOEs) used in this study include queue delay, queue length, vehicle delay and stopped delay.

This study obtain traffic turning movements and signal timing data from the Ohio

Department of Transportation (ODOT). The turning movement counts (TMC) were taken from ODOT’s Transportation Data Management System for the year 2017. VISSIM version 11 software was used for microscopic simulation. The optimum signal phasing for the three interchange designs were obtained from SYNCHRO 10 software based on the PM peak hour traffic data. The virtual interchange network design geometry in both software programs were almost identical. Several assumptions were made to stay consistent as much as possible while comparing the three designs since they have completely different geometric layouts. For example, the existing CDI data included the through movements from off-ramps to on-ramps. Since the two alternative designs (SPUI and DDI) exclude the through movements from off-ramps to on-ramps, their data were added to the right turn

v movements. Moreover, the speed limit was set to be in the range of 30 mph while driving in the interchange to meet all three design specifications.

The analysis of results show that there are significant advantages and disadvantages associated with each design (CDI, SPUI and DDI). During implementation, various factors such as cost, efficiency, safety, delay, etc., need to be considered when attempting to select the best design, which would be the most appropriate method as these may vary from situation to situation. However, in the current study, a DDI performed best, followed by a

SPUI, and then CDI was last. Moreover, CDI with its signal timing optimized very highly improved all MOEs considered when compared with the CDI with existing signal timing.

DEDICATION

Dedicated to my backbone who believed in my capabilities.

Thanks for holding me together to be the strong woman that I am today.

Thank you so much Mom without your love and support I wouldn’t reach this point.

vii

ACKNOWLEDGMENTS

To begin, special thanks to the Almighty God for this opportunity and all the graces in my life. I wouldn’t accomplish anything without God’s will. Also, my gratitude goes to my principal advisor, Dr. Deogratias Eustace who helped me finish this thesis and supported me to overcome all the obstacles I’ve been through.

I would like to express my appreciation to Dr. Philip Appiah-Kubi who also helped me hold onto this thesis until the end. His kind words were always on top of my head whenever I was down. Also, many thanks go to Eng. Charlie Fisher of ODOT who provided me the data I needed for this thesis study. Thanks Eng. Paul Goodhue for serving on my thesis committee and providing me comments that helped to improve my report.

Finally, I’m thankful to my family for their encouragement. I wouldn’t succeed in my educational life without your support. Thanks to those who shared even a single thought about this thesis; sharing your knowledge means a lot to me.

viii

TABLE OF CONTENTS

ABSTRACT ...... iv

DEDICATION ...... vii

ACKNOWLEDGMENTS ...... viii

LIST OF FIGURES ...... xii

LIST OF TABLES ...... xiv

LIST OF SYMBOLS/ABBREVIATIONS ...... xv

CHAPTER I INTRODUCTION ...... 1

1.1 Introduction ...... 1

1.1.1 Conventional Diamond Interchanges (CDIs) ...... 2

1.1.2 Single Point Urban Interchanges (SPUIs) ...... 3

1.1.3 Diverging Diamond Interchanges (DDIs) ...... 4

1.2 Problem Statement ...... 4

1.3 Objectives of Study ...... 6

1.4 Organization of the Thesis Report ...... 7

CHAPTER II LITERATURE REVIEW ...... 9

2.1 Introduction ...... 9

2.2 Alternative Interchange Designs ...... 10

2.3 Common Interchanges and their Characteristics ...... 11

2.3.1 Diamond Interchanges (DIs) ...... 11

2.3.2 Directional Interchanges ...... 12

2.3.3 Diverging Diamond Interchanges (DDIs) ...... 12

2.3.4 Single Point Urban Interchanges (SPUIs) ...... 13

2.4 Recent Research ...... 13

2.5 Earlier Research ...... 14

CHAPTER III METHODOLOGY AND DATA COLLECTION ...... 21

3.1 Source of Data ...... 21

3.2 Signal Optimization using SYNCHRO 10 ...... 24

3.3 Methodology ...... 27

3.3.1 Use of Traffic Simulation Software ...... 27

3.3.2 VISSIM Simulation ...... 27

CHAPTER IV RESULTS AND DISCUSSION...... 37

4.1 Measurements of Efficiency (MOEs) ...... 37

4.2 Overall Level of Service (LOS) Comparison ...... 41

4.3 Known Advantages and Disadvantages of SPUI and DDI...... 42

4.3.1 The Single Point Urban Interchange ...... 42

4.3.2 The Diverging Diamond Interchange ...... 43

CHAPTER V CONCLUSIONS AND RECOMMENDATIONS ...... 44

5.1 Conclusions ...... 44

5.2 Recommendations ...... 45

REFERENCES ...... 46

APPENDIX A SPUI 12/05/2017 Volume Data...... 52

LIST OF FIGURES

Figure 1.1 Visual representation of a conventional diamond interchange (Sharma and

Chatterjee, 2007) ...... 2

Figure 3.1 The Current Conventional Diamond Interchange ...... 21

Figure 3.2 Turning Movement Counts for Location ID 82157 ...... 22

Figure 3.3 Turning Movement Counts for Location ID 82257 ...... 23

Figure 3.4 The Conventional Diamond Interchange Design in SYNCHRO for 2011

Traffic Volumes ...... 24

Figure 3.5 The Existing Conventional Diamond Interchange Design in SYNCHRO ...... 25

Figure 3.6 The Proposed Single Point Urban Interchange Design in SYNCHRO ...... 26

Figure 3.7 The Proposed Diverging Diamond Interchange Design in SYNCHRO ...... 26

Figure 3.8 CDI VISSIM Network ...... 28

Figure 3.9 SPUI VISSIM Network ...... 28

Figure 3.10 DDI VISSIM Network ...... 29

Figure 3.11 SPUI Ring Barrier Controller ...... 30

Figure 3.12 DDI 1st Ring Barrier Controller ...... 31

Figure 3.13 DDI 2nd Ring Barrier Controller ...... 32

Figure 3.14 CDI 1st Ring Barrier Controller – Original Signal Timing...... 33

Figure 3.15 CDI 2nd Ring Barrier Controller – Original Signal Timing ...... 34

Figure 3.16 CDI 1st Ring Barrier Controller – Optimized Signal Timing ...... 35

Figure 3.17 CDI 2nd Ring Barrier Controller – Optimized Signal Timing ...... 36

Figure 4.1 Queue Delay Results ...... 39

Figure 4.2 Queue Length Results...... 39

xii

Figure 4.3 Vehicle Delay Results ...... 40

Figure 4.4 Stopped Delay Results ...... 41

xiii

LIST OF TABLES

Table 1.1 Traffic Volume Increase Within a 6-Year Period ...... 6

Table 3.1 PM Peak Hour Data for Location ID 82157 ...... 22

Table 3.2 PM Peak Hour Data for Location ID 82257 ...... 23

Table 4.1 PTV VISSIM User Manual Results Description ...... 37

Table 4.2 VISSIM LOS Node Results ...... 41

xiv

LIST OF SYMBOLS/ABBREVIATIONS

AAA American Automobile Association

AASHTO The American Association of State Highway and

Transportation Officials

BTS Bureau of Transportation Statistics

CDI Conventional Diamond Interchange

DDI Diverging Diamond Interchange

DIs Diamond Interchanges

DXI Double Crossover Intersection

FHWA Federal Highway Administration

MOEs The Measurements of Efficiency

NHTSA The National Highway Transportation Safety Administration

ParClo Partial Cloverleaf

SPUI Single Point Urban Interchange

TDI Tight Diamond Interchange

TMC Turning Movement Counts

CHAPTER I

INTRODUCTION

1.1 Introduction

The number of registered vehicles in the United States has dramatically increased throughout the last six decades. The Bureau of Transportation Statistics (BTS), a division of the US Department of Transportation (USDOT) collects and publishes annual transportation statistical data for a number of areas of interest related to transportation, including the annual number of registered vehicles in the country. According to BTS

(2018), there were 74,431,800 registered vehicles in the United States in 1960 but in 2016

(the most recent data available), there were 268,799,083 registered vehicles in the country.

In less than six decades, the number of registered vehicles in the country has increased more than 3.6 times.

Highway facilities constructed in the 1960s and 1970s were not designed to handle vehicular traffic of these proportions. Bicycle riders and pedestrians encounter difficulties and significant risk of physical harm while attempting to cross at heavily travelled intersections (Yang et al., 2014). In response to these growing safety risks, federal and state departments of transportation developed innovative traffic engineering approaches to improve intersection safety for drivers, cyclists, and pedestrians (Yang et al., 2014). These innovative efforts led to the development of system interchange, which use a series of connectors and ramps to guide motorists from one highway to another, and service interchange, which connects a freeway with local surface streets or arterials. Service interchanges must provide an appropriate balance between regional mobility and local road access (Doctor et al., 2009). Within the broad categories of service and system interchanges

1 exist different types of interchanges including cloverleaf, partial cloverleaf, diamond, diverging diamond (also called double crossover diamond), and single-point urban interchange (Doctor et al., 2009).

1.1.1 Conventional Diamond Interchanges (CDIs)

CDIs are termed to be the easiest design in creating crossover movements

(Chlewicki, 2003). It is a type of interchange wherein two on-ramps and two-off ramps assist the connection of the freeway to the crossroad (Sharma and Chatterjee, 2007). Figure

1.1 shows the schematic diagram of a typical CDI.

Figure 1.1 Visual representation of a conventional diamond interchange (Sharma and Chatterjee, 2007)

Typically, the distance between two ramps is 500 ft, however, the study of Song and

Yang (2012) suggested that the separation should be 800 ft or more. The radii of the crossover movements and the left-turn movement are ranging from 150 ft to 200 ft and 100

2 ft, respectively. The two separate intersections of CDI are often closely-spaced and are not of independent systems, rather, interacting with each other (Hook and Upchurch, 1992).

Given this, the operation of one will be affected by another. Three common phases are used for CDIs: (1) three-phase, (2) four-phase, and (3) four-phase with overlap. Various simulations comparing the DDI and CDI show that DDI has better results compared to that of the CDI. According to a study by Chlewicki (2003), the total delay for a CDI is three times of the DDI, the stop delay is 4 times, and the total stops is twice.

1.1.2 Single Point Urban Interchanges (SPUIs)

The first SPUIs in the US were developed in 1970 to increase the amount of traffic that can be safely sustained at busy intersections (Hughes et al., 2010). SPUIs are frequently used at intersections with a narrow or restricted right of way; the design intersects the four vehicle turning motions at a central location (Qureshi et al., 2004). This central location can be set on a highway underpass or a highway overpass (Hughes et al.,

2010). Large bridges are a necessary element of SPUIs because the bridge in this interchange design contains a large sized deck; this requirement makes this design of interchange very expensive to develop and implement (Qureshi et al., 2004).

SPUIs are a version of a compressed diamond interchange design model (Hughes et al., 2010). Because of the space restrictions, when developing a SPUI, certain design elements must be taken into consideration, including (i) the number of left-turning lanes, right-turning lanes, and through lanes, (ii) concrete island, (iii) the width of the road median, and (iv) the skew angle (Hughes et al., 2010). The bridge span (length) is also a significant factor; depending on the geometric design structure of the bridge that will be

3 used with a SPUI, the span or length of the bridge should measure between 160 ft to 280 ft (Hughes et al., 2010).

1.1.3 Diverging Diamond Interchanges (DDIs)

Diamond interchanges (DIs) are designed to allow motorists to cross each other as they are making left-hand turns (Qureshi et al., 2004). Depending on the timing of the traffic signal, motorists who want to make a turn may have to wait through multiple traffic signal cycles before they receive the signal to successfully navigate the turn (Qureshi et al.,

2004). There are multiple design types of DIs that can be employed, depending on the specific needs of the intersection and community. One model of DI is DDI, which are diamond exchanges that are specifically designed to support substantial numbers of motorists navigating left-turning motions in an efficient manner, which includes the use of a crossroad and access to a ramp that is controlled by traffic signals (Edara et al., 2015).

Motor vehicles on the crossroad shift to the left side of the highway to access the designated lanes that are situated between the traffic ramp signals (Edara et al., 2015). The first DDI in the US was built in 2009 in Springfield, Missouri by the Missouri Department of

Transportation (Edara et al., 2015).

1.2 Problem Statement

The number of vehicles plying on US roadways has exponentially increased over the last five decades. The nation’s system of highways that were developed and built forty years ago were not designed to handle the massive volumes of motor vehicles that currently utilize them. Motorists are experiencing longer commute times due to heavy vehicle traffic

4 on local roads, state highways, turnpike highway systems, and interstate highway systems.

Traffic is slowed down due to inadequate capacity to accommodate high traffic volumes, road construction, crashes, detours, motorists waiting to make left turning movements or right turning movements; these are some of the road hazards that exist today. An increased volume of motor vehicle traffic at heavily traveled interchanges heightens the risk of a single or multiple vehicle crashes, especially at junctions that are not equipped to manage high volumes of vehicular traffic, creating an additional safety risks to all road users.

Traffic engineers from state and federal departments of transportation have responded to calls for safer roads and interchanges in some areas by developing and implementing interchanges at locations identified as dangerous because of an increase in fatal and non-fatal motor vehicle crashes. Traffic engineers have a multitude of tools at their disposal to analyze problematic locations, conduct a series of assessments and studies before developing solutions to resolve traffic issues. Two of the solutions that have been employed by traffic engineers in solving freeways’ junctions include the use of single-point urban interchanges (SPUIs) and diverging diamond interchanges (DDIs). Both interchanges have different designs and are used for different purposes to meet specific needs based on different criteria such as location, traffic situation, and existing infrastructure.

An existing conventional diamond interchange located in southwestern Ohio was selected to compare the traffic flow efficiency and the performance of the proposed designs. The reason for selecting this specific interchange is that the adjacent area (Austin

Landing shopping center) is extremely growing at such a pace that the interchange is experiencing traffic congestion and ODOT claims that the 2016 traffic volume already

5 exceeded the predicted design volume for the year 2035 (Loveland et al., 2016). This is a relatively new interchange, it was open to traffic for the first time on July 2, 2010. Table

1.1 shows traffic volume increase from 2011 to 2017. The volume increased by 36% for the southbound left-turn (SBL) movement in the direction heading to Austin Landing area

(first crossover location). Also, there is a 93% increase in the northbound right-turn (NBR) movement, which also heads towards the Austin Landing area and by 37% for the eastbound through (EBT) movement (second crossover location).

Table 1.1 Traffic Volume Increase Within a 6-Year Period

Crossover % Change in 6 Movement 2011 Volume 2017 Volume Location Years SBR 200 299 50% SBL 892 1210 36% Crossover EBT 417 583 40% Location 1 EBR 44 175 298% WBT 558 662 19% WBL 303 608 101% NBR 289 558 93% NBL 121 232 92% Crossover WBT 717 1052 47% Location 2 WBR 538 1029 91% EBT 1175 1614 37% EBL 155 256 65%

1.3 Objectives of Study

Professional traffic engineers are tasked with addressing issues related to traffic flow analysis and model development. These once manual processes are now completed with computer software programs. The objective of this study is to conduct a comparative analysis of a single point urban interchange (SPUI) and a diverging diamond interchange

(DDI) with the existing conventional diamond interchange (CDI) for similar traffic

6 situations using PTV VISSIM traffic simulation modeling software. The virtual models of all three interchange types were employed to compare the efficiency of traffic flows over a CDI, a SPUI, and a DDI system. The analysis of the three interchange models is used to gather the required information to determine if one interchange design performs better than the other by using the selected MoEs, namely traffic queue length, traffic queue delay, vehicle delay, and stopped delay. The traffic data used in the current study was counted during a peak hour for the location which is currently designed as a conventional diamond interchange. The existing CDI interchange layout was first developed in Synchro 10 software and by using existing signal timing and the 2017 peak hour turning counts, the existing scenario was created. Then Synchro was used to optimize the signal timing. The existing CDI and the virtual design models of SPUI and DDI were compared by use of their level of service and other MOEs already described above obtained from VISSIM.

1.4 Organization of the Thesis Report

This thesis report is arranged into five detailed chapters as follows:

Chapter 1: Introduction – First, it starts with a general background about United States

highways and their need to be reconstructed. Then it introduces some of the

solutions and general information about CDIs, SPUIs and DDIs. The

introduction chapter is wrapped up with a problem statement and a study

objective.

Chapter 2: Literature Review – This chapter is divided into five subtitles. The first three

present an overview of interchanges information and common types of

interchanges with their characteristics. The fourth and fifth subtopics are mainly

about recent and earlier researches.

Chapter 3: Methodology and Data Collection – In this chapter, the first subtopic presents

the source of data and how these data were modified to fit each design. The

signal timing and phases, which were optimized using SYNCHRO are covered

next. After that, the methodology part follows, which mostly show how the

VISSIM models were developed so the simulation can run efficiently.

Chapter 4: Results and Discussion – This chapter presents the results of the study which

are contrived and discussed in descriptive paragraphs.

Chapter 5: Conclusions and Recommendations – In this chapter, the conclusions of the

study are stated followed with some recommendations for further researches.

CHAPTER II

LITERATURE REVIEW

2.1 Introduction

The Missouri Department of Transportation (MoDOT) describes an intersection as a location where at least two roads or more cross at each other at the same surface level

(Maerz et al., 2005). An interchange is a type of intersection at a location where one road passes over another road and are connected by ramps; it is also known as a grade-separated intersection (Maerz et al., 2005). Intersections are prone to heavy vehicle congestion during times of high volume traffic (e.g., morning and evening rush hours, construction and crash detours, etc.), creating commuter delays, and posing a substantial safety risk (Maerz et al.,

2005). According to the Federal Highway Administration (FHWA), approximately 25% of traffic-related fatalities and nearly 50% of traffic-related injuries occur at intersections

(Maerz et al., 2005). A multitude of solutions and strategies are available to traffic and highway engineers to address these issues, including installation of traffic control mechanisms like markings, signals, and signs, and linear or geometric design changes

(Maerz et al., 2005).

In response to concerns regarding motorist, pedestrian, and bicyclist safety at intersections and interchanges; cost; development; environmental considerations; politics; and traffic volume, state and federal departments of transportation (DOTs) have responded by developing and installing interchanges (Maerz et al., 2005). Globally, hundreds of interchanges have been constructed, with many of them uniquely designed to meet specific motorist and community requirements (Maerz et al., 2005). In the United States, there are

9 a number of public and private agencies that are committed to improving highway safety, and reducing the number of highway injuries and fatalities, including the American

Automobile Association (AAA); the American Association of State Highway and

Transportation Officials (AASHTO), Federal Highway Administration (FHWA); the

Institute of Transportation Engineers (ITE); and the National Highway Transportation

Safety Administration (NHTSA), to name a few (Garber and Rivera, 2010). Smith and

Garber (1998) developed guidelines for traffic engineers to select the right single-point urban or diamond interchanges.

2.2 Alternative Interchange Designs

The Federal Highway Administration (FHWA) developed a comprehensive report that provides an overview of alternative intersection and interchange designs for highway junctions in place of grade-separated diamond interchanges and traditional at-grade intersections to alleviate traffic congestion, and improve overall safety for motorists, bicyclists, and pedestrians (Hughes et al., 2010). The alternative interchange designs discussed in the FHWA’s document include alternative diamond interchanges (DIs), single point urban interchange (SPUI), and tight urban diamond interchange (TUDI) (Hughes et al., 2010). There are several standard and customized interchanges that can be developed to address specific, unique requirements. Some examples of interchanges used throughout the country are described next.

2.3 Common Interchanges and their Characteristics

Commonly used interchanges include cloverleaf, diamond, and directional (Edara et

al., 2015). Cloverleaf interchanges are easily identified by their namesake cloverleaf shape.

This interchange model is utilized in a highway infrastructure where two high traffic

roadways intersect with each other (Edara et al., 2015). Therefore, they are typically system

interchanges, where they are designed to connect freeway to freeway facilities. Left turns

are enabled with the inclusion of loop-shaped ramps (Edara et al., 2015). The cloverleaf

interchange design uses a significant amount of right of way space and is designed with

sections to accommodate motor vehicle traffic as it enters and exits the interchange (Edara

et al., 2015). Speeds on the loops are always lower, typically 25-35 mi/h due to driving on

the curved ramps with generally tight radii.

2.3.1 Diamond Interchanges (DIs)

DIs are the most frequently used configuration and can be utilized in city and rural

communities (Edara et al., 2015). Higher volumes of motor vehicle traffic turning left on

the interchange crossroad can create congestion; this design typically includes the use of

traffic signals to control access to the on- and off-ramp connected to the crossroad (Edara

et al., 2015). Thus, these are typically service interchanges, where they are designed to

connect local surface roads (i.e., arterials or collectors) to freeway facilities. When

developing a diamond interchange design, it is important to ensure adequate space exists

between the on- and off-ramps to facilitate a normal flow of traffic as it travels through the

interchange (Edara et al., 2015).

2.3.2 Directional Interchanges

Directional interchanges are designed to manage a high volume of turning movements at the intersection of two highways (Edara et al., 2015). Directional interchanges are equipped with direct ramps to facilitate higher speeds (typically higher than 45 mi/h), reduce the distance traveled, increase vehicle capacity, prevent vehicles from weaving, and eliminate the need for motorists to engage in additional travel if they need to change direction (Edara et al., 2015). Thus, they are typically system interchanges, where they are designed to connect freeway to freeway facilities and are commonly utilized for urban freeways with very high traffic volumes. The addition of bridge crossing extra ramps, and significantly longer ramps make this interchange model very expensive to build (Edara et al., 2015).

2.3.3 Diverging Diamond Interchanges (DDIs)

DDIs are utilized to reduce traffic congestion and improve the flow of traffic by eliminating the need for left-turning signaling devices (Lloyd, 2016). The geometric variances between traditional diamond interchange designs and the diverging diamond interchanges found in the crossover design directs traffic to migrate to the other side of the road to create space for left turns for access to the on ramp to enter the highway and enable left turns from the highway off ramp to reach the crossroad (Lloyd, 2016). This design facilitates both normal traffic flow and left turns without either vehicle movement obstructing the opposing movement (Lloyd, 2016). Each set of on and off ramps are equipped with dual phase signals to control the flow of traffic (Schroeder et al., as cited in

Lloyd, 2016). The volume of conflict points in DDI design is reduced from the twenty-six

12 conflict points contained in standard diamond interchange design to fourteen points

(Siromaskul, 2010, as cited in Lloyd, 2016).

2.3.4 Single Point Urban Interchanges (SPUIs)

Diamond interchange is the most common design with SPUIs growing in popularity

(Bared et al., 2005). SPUI is similar to the tight diamond interchange (TDI) except the ramp terminals join at one crossing with one signal (Bared et al., 2005). SPUI is distinguished by its ability to allow concurrent left turns from the off ramp (Bared et al.,

2005). SPUIs have a substantially higher rate of clearance lost times during arterial through movements and left turning ramp movements (Hook and Upchurch, 1992). TDIs equipped with 200ft to 400ft off rap terminal offsets are a lower cost alternative to SPUIs because of fewer construction requirements and fewer right-of-way requirements (Bared et al., 2005).

2.4 Recent Research

Interchange studies completed this decade centered on the evaluation of specific interchanges (Khan and Anderson, 2016); performance (Tarko, 2017); safety (Abatan and

Savolainen, 2018; Edara et al., 2015; Lloyd, 2016); and the use of PTV VISSIM microsimulation software (Schroeder et al., 2014) for traffic simulation and traffic planning. In the area of safety, studies have been conducted to assess the performance of interchanges. A study by Abatan and Savolainen, (2018) assessed the safety performance of the functional areas of interchanges using motor vehicle crash data over a multiyear span. Traffic data including traffic volume, frequency of accidents, and highway geometrics were used to determine whether a correlation could be found between these

13 variables and the number of motor vehicle crashes that occurred within the identified functional areas of the interchange. The results of this study found a correlation between vehicle travel speeds and interchange design: reduced ramp speeds correlated with a reduction in ramp-related crashes (Abatan and Savolainen, 2018).

Galletebeitia (2011) compared the diverging diamond interchange and the partial cloverleaf interchange using microsimulation modeling. That study assessed the diverging diamond interchange (DDI) which has an unconventional design compared to partial cloverleaf (ParClo) interchange. Galletebeitia (2011) evaluated the differences in terms of measure of effectiveness (MOEs). The first part of the methodology described the different characteristics such as the number of ramps as well as the geometry for each design whereas the second part described the type of micro-simulation used to compare the different interchange designs. The different measures of effectiveness extracted from microsimulation were defined to understand what measures would be used to conduct the comparison. The end results show that the maximum queue length on a ParClo occurs at the off ramps where vehicles are trying to enter the crossroad but are unable to do so since the crossroad is very congested. In conclusion, as the flows increased the difference between the delay time, stop time and number of stops of the DDI with through lanes and the ParClo decreased to the point where the above mentioned MOEs almost came to be equal (Galletebeitia, 2011).

2.5 Earlier Research

Earlier studies centered on topics such as comparative analyses (Leisch et al., 1989); evaluation tools (Radwan and Hatton, 1990); traffic pattern analysis (Poppe et al., 1991);

14 operational efficiency (Bonneson, 1992); design (Qureshi et al., 2004); and microsimulation tools (Fang and Elefteriadou, 2005). In 1993, the Florida Department of

Transportation conducted a study to determine the practicality of employing grade separators to mitigate congestion at arterial intersections and nearby arterial roads (Fowler,

1993). One of the elements of the study was to conduct a comparison between the traffic flow capacities of a single point urban interchange (SPUI) and tight diamond interchange

(TDI) (Fowler, 1993). Earlier research studies on SPUI and TDI comparisons were incomplete, poorly conducted, or inconsistent (Fowler, 1993); this made the data unreliable and unusable for future research. The issues with previous SPUI and TDI comparative analyses identified by Fowler (1993) were that some studies utilized traffic volume data and others did not, with some failing to provide evidence to support their rationale; some studies had incomplete descriptions of their research assumptions and methodologies used

(Fowler, 1993).

Some of the credible studies Fowler did locate noted during the comparisons between

SPUI and TDI. The results were affected by the amount of traffic at the time the data was gathered (Fowler, 1993). At the end Fowler (1993) concluded that the most effective and accurate comparison between SPUI and TDI would require performing two sets of tests, one test would be a rapid analysis to identify the traffic volume traits that impacted the amount of traffic the interchanges could manage; the second, more comprehensive test would be completed after the traffic volume traits from the rapid analysis were identified.

Few comparative studies between SPUI and TUDI had been completed despite their geometric dissimilarities; this makes it difficult to determine the best alternative interchange for a given location (Jones and Selinger, 2003). A 2002 comparative analysis

15 of traffic operations performance between SPUI and TUDI in a range of traffic volume conditions utilizing CORSIM microscopic simulation software with signal phasing and timing found SPUI had better traffic operation performance in higher traffic capacity, greater average travel speeds, less phase failures, and fewer stops than TUDI (Jones and

Selinger, 2003). Average SPUI operating conditions equaled TUDI maximum capacity

(Jones and Selinger, 2003).

A study between Double Crossover Intersection (DXI) and DDI showed DXI has fewer delays, stops, shorter traffic queues, and stop time; and higher performance (Bared et al., 2005). DXI is configured with additional signals at the through lanes at the intersection’s crisscross, which poses a safety risk (Bared et al., 2005). DDI offers fewer delays, stops, shorter traffic queues, and stop time; increased performance; higher signal capacity than conventional diamond (Bared et al., 2005). DDI design is preferable to conventional diamond design (CDI) because left-turn only lanes are not required (Bared et al., 2005). DDIs design promotes safety because they reduce the crash frequency between motorists turning left on the highway and opposing traffic (Bared et al., 2007). A study by

Sharma and Chatterjee (2007) found that a DDI performed better than a CDI with fewer delays, reduced travel time, reduced traffic queues, less signal phases, and higher left turn capacity. Double Crossover Intersections (DXIs) had fewer delays and higher performance than DDIs and similar volumes of through movements (Edara et al., 2015). DDIs perform better than DXIs in high volume traffic with fewer stops, delays, stop times and shorter vehicles queues (Edara et al., 2015).

The tight urban diamond interchange (TUDI) is an adaptation of conventional diamond interchange, with TUDI equipped with tightly spaced ramp terminals (Jones and

Selinger, 2003). TUDIs are usually equipped with ramp terminals placed 200 ft to 400 ft from each other; both ramp intersections have traffic signal controls that are coordinated to facilitate the flow of traffic through the intersections (Jones and Selinger, 2003). The single point urban interchange (SPUI) is an adaptation of TUDI as all lanes converge at a single intersection located above or below the main highway, with one signal controlling the intersection with three phase timing and overlaps (Jones and Selinger, 2003). Three phase timing patterns are used because of SPUIs unique design/operational feature: all left turning movements travel are inverted (i.e., travel to the inside of each other) to reduce the frequency of left turn difficulties that typically occur at traditional roadway intersections and lowers the number of required phases from four to three (Jones and Selinger, 2003).

SPUI and TUDI have become more common to improve highway volume capacity in developed regions that do not require extra right of way space (Jones and Selinger,

2003). Very few studies of the safety performance of SPUI and TDI have been conducted

(Bared et al., 2005). Bared et al., (2005) compared accident data from SPUI and TDI for intersection related crashes on the crossroad for SPUIs without frontage roads using a negative binomial model; to predict total accidents and injury and fatal incidents using crossroad flow, off ramp flow and the distance in separation between the right and left ramp terminals using Wilcoxon signed-rank test; no significant safety differences (Bared, et al., 379). The SPUI and DI accident data was compared and indicated SPUIs were safer

(Bared et al., 2005)

A study by Garber and Smith (1996) compared the operational and safety characteristics of the single point urban and diamond interchanges. This study analyzed the operational and accident characteristics of single point urban and diamond interchange.

The results from Garber and Smith, 1996 study show that the compressed DI was more efficient than the SPUI. They also noted that the volumes consisted of heavy through traffic and heavy unbalanced left turns. In one case the SPUI was more efficient as all the left turns were heavy and the through traffic was light. In conclusion, they say the compressed

DI was more efficient than the single point DI for high traffic volumes. The compressed

DI was noted to be able to accommodate greater variability of traffic patterns (Garber and

Smith, 1996).

Smith and Garber (1998) studied the guidelines for selecting single-point urban and diamond interchanges. The study analyzes and compares the operational and safety characteristics of the SPUI and the DI. They used a questionnaire to obtain data from relevant traffic engineers regarding the safety and operational features of the SPUI. Their results show that major factors affecting the selection of the SPUI could increase capacity, decrease congestion, minimize delay, and simplify arterial coordination. Smith and Garber

(1998) conclude that although SPUI is considered fairly a new design, its use is expanding.

Particular circumstances and operational factors influence the selection of the SPUI instead of DI and vice versa (Smith and Garber, 1998).

A study by Hook and Upchurch (2003) explored the operational differences between the single-point diamond interchange (SPDI) and the conventional diamond interchange

(CDI). They measured headway and lost time at seven interchanges. Their results indicate that SPDI has a marginally higher saturation flow rate which is not statistically significant.

The arterial dedicated left turn movement is much higher for the single-point diamond interchange but the results are not significantly different. They also conclude that the two

18 interchange forms have similar flow rates owing to a similar saturation flow (Hook and

Upchurch, 2003).

Bonneson (1992) studied the operational efficiency of the single-point urban interchange. The study examines the effects that SPUI size have on phase capacity as well as motorist delay. Their methodology comprised of three tasks. First, the mean and standard deviation were calculated for the start-up lost time, discharge headway, free flow speed, and end use. Secondly, factors influencing these variables were recognized through evaluation of variance techniques. Lastly, the significance of influential factors and model parameters was assessed using least squares methods. Their results indicate that the capacity decreases with increasing clearance path length and return radius. In general, the effect of radius on the left turn capacity appears to be relatively small. In conclusion, their analysis suggests that they might not be a significant difference in capacity and delay between small and large SPUIs without frontage roads (Bonneson, 1992).

Afshar et al. (2009) compared traffic between the single point and the diverging diamond grade-separated interchanges. The methodology involved the use of the concept of critical lane volume (CLV) to cancel the effects of geometry and different number of lanes thereby making the two designs comparable. The designs were tested for several traffic scenarios and delay measures were accounted for such as average delay and an average number of stops. After the designs were tested, it was noted that CLV in the SPI remained relatively constant over all scenarios whereby all traffic volumes were balanced.

Though moving from left to right the traffic volumes became more unbalanced and the

CLV of the SPI slightly decreased. The performance of the DDI was more dependent on the directional split of opposing traffic volumes. However, its performance improved as

19 the traffic became more unbalanced. In conclusion, the performance of the SPI and the DDI carried out does show the directional distribution of the traffic is one of the key criteria that should be considered when deciding whether SPI or a DDI would be the best fit (Afshar et al., 2009).

CHAPTER III

METHODOLOGY AND DATA COLLECTION

3.1 Source of Data

For the current study, actual data for a Conventional Diamond Interchange (CDI) located in Montgomery County in Ohio were provided by the Ohio Department of

Transportation (ODOT). The count date for the specified location was Tuesday, December

5th, 2017. Figure 3.1 shows the location and the Interchange ID numbers as known in the

ODOT database to simplify the process of searching for the data needed. The Turning

Movement Counts (TMC) for the PM peak hour were downloaded from the transportation

Data Management System. Table 3.1 and Figure 3.2, which cover the data for the first location in the existing interchange, best simplify the data used as the input in the virtual models as well as Table 3.2 and Figure 3.3 for the second location in the CDI.

Figure 3.1 The Current Conventional Diamond Interchange

Table 3.1 PM Peak Hour Data for Location ID 82157 PM Peak Hour Cars 4:45 PM - 5:30 PM ID 82157 and (12/05/2017) Trucks EB SB WB Hourly L T R Total L T R Total L T R Total Volume 0 583 175 758 1,210 2 299 1,511 608 662 0 1,270 App % 0% 77% 23% 80% 0% 20% 48% 52% 0% PHF 0.91 0.65 0.83 0.93 0.5 0.88 0.94 0.85 0.89 0.87 HV % 1% 3% 2% 1% 3% 1% 1% 1% 1% Total % 0% 16% 5% 21% 34% 0% 8% 43% 17% 19% 0% 36%

Figure 3.2 Turning Movement Counts for Location ID 82157

Table 3.2 PM Peak Hour Data for Location ID 82257

PM Peak Hour Cars 4:45 PM - 5:30 PM ID 82257 and (12/05/2017) Trucks NB EB WB

Hourly L T R Total L T R Total L T R Total Volume 232 3 558 793 256 1,614 0 1,870 0 1,052 1,029 2,081 App % 29% 0% 70% 14% 86% 0% 0% 51% 49% PHF 0.88 0.38 0.89 0.94 0.72 0.9 0.94 0.83 0.85 0.87 HV % 0% 1% 1% 2% 1% 1% 1% 2% 2% Total % 5% 0% 12% 17% 5% 34% 0% 39% 0% 22% 22% 44%

Figure 3.3 Turning Movement Counts for Location ID 82257

Due to the special geometry of each virtual model, some assumptions were made to develop the simulation with a rational traffic flow for the SPUI and DDI designs. The CDI allows a through movement coming from the off ramps going to the on ramps, neither the

SPUI nor the DDI models for this study allows it. The traffic volume data for that through movement were added to the right movement data going to the west and east bounds on the arterial road (Austin Boulevard). The west and east bounds needed some adjustments in the traffic flow inputs since the CDI differs in its geometry and operation.

3.2 Signal Optimization using SYNCHRO 10

The SYNCHRO file for the existing CDI was provide by ODOT. For the design year

2011 the signal functioned well in that interchange as seen in Figure 3.4. With the new volume increase the signal timing needed to be optimized to maintain a smooth traffic flow.

As seen in Figure 3.5 the CDI model for 2017 traffic data provided by ODOT was designed to optimize the traffic signal timing.

Figure 3.4 The Conventional Diamond Interchange Design in SYNCHRO for 2011 Traffic Volumes

Figure 3.5 The Existing Conventional Diamond Interchange Design in SYNCHRO

The signal designs and interchange layouts were also developed in SYNCHRO 10 software for each model, SPUI and DDI. The optimum signal timing results for the PM peak hour for all three interchange types were used later in PTV VISSIM simulation. The virtual model network characteristics including the number of lanes, speed, signal phases, vehicle volumes and the layout dimensions were almost consistent in both software so that the simulation runs efficiently. Figures 3.6 and 3.7 are screenshots showing the intersection network models and traffic volumes that were used in SYNCHRO to optimize the traffic signals timing.

Figure 3.6 The Proposed Single Point Urban Interchange Design in SYNCHRO

Figure 3.7 The Proposed Diverging Diamond Interchange Design in SYNCHRO

3.3 Methodology

3.3.1 Use of Traffic Simulation Software

Traffic simulation systems are computer-based software programs that model

dynamic traffic flows for a specific location over time (Fang and Elefteriadou, 2005).

Traffic simulation models can be used to analyze complex issues that analytical

methodologies would not sufficiently address, and to test alternative scenarios without

risky and expensive (Fang and Elefteriadou, 2005). Traffic simulation systems have

become important traffic operational analytical tools (Fang and Elefteriadou, 2005). In

order to improve the traffic flow and safety, microsimulation techniques are being

considered all around the word by traffic engineers. It is an effective way to simulate the

performance of a new or an upcoming transportation infrastructure. VISSIM was used to

generate and collect the performance measures data needed for the alternative designs.

3.3.2 VISSIM Simulation

Before the VISSIM model can be simulated, some steps need to be followed in each

design. The first step is to develop the network and adjust the model by adding links and

connectors. Figures 3.8 through 3.10 show the models developed in VISSIM for the

simulation of the three types interchange CDI, SPUI, and DDI. The units also need to be

specified as well as the desired speed, vehicle class, vehicle type, reduced speed areas and

conflict areas. Some components can be left as the default setting if not specified to be

changed based on the study scenarios. The second step is the data input which includes the

vehicle input and the vehicle route. Under the vehicle input, the total vehicle volumes

should be added. The vehicle composition depends on the vehicle types that you set for the

27 analysis which are cars and trucks for this study. The percentage of each type should be indicated based on the volume data taken from the ODOT website. For the vehicle route, the percentage of the moving vehicles must be noted as well as their direction and movement. Some assumptions were made for the data to fit in the SPUI design (see appendix for further details).

Figure 3.8 CDI VISSIM Network

Figure 3.9 SPUI VISSIM Network

Figure 3.10 DDI VISSIM Network

The third step is the signal data, in this analysis the data were developed and taken from SYNCHRO. Some adjustments were made for both designs to run the simulation in

VISSIM. In the SPUI traffic signal design, one controller was set to control the three phases as seen in figure 3.11. In the DDI design, two controllers were used to add the phases needed in each junction. Figures 3.12 and 3.13 show the timing for every phase in the proposed DDI.

Figure 3.11 SPUI Ring Barrier Controller

Figure 3.12 DDI 1st Ring Barrier Controller

Figure 3.13 DDI 2nd Ring Barrier Controller

For the original volumes provided by ODOT, the signal timing set for the CDI are shown in Figures 3.14 and 3.15. The optimized signal timing for the existing CDI interchange with the 2017 traffic volumes are shown in Figures 3.16 and 3.17. The existing

CDI was reconsidered and simulated in VISSIM to compare the efficiency of all the alternatives.

Figure 3.14 CDI 1st Ring Barrier Controller – Original Signal Timing

Figure 3.15 CDI 2nd Ring Barrier Controller – Original Signal Timing

Figure 3.16 CDI 1st Ring Barrier Controller – Optimized Signal Timing

Figure 3.17 CDI 2nd Ring Barrier Controller – Optimized Signal Timing

The last step to accomplish a full VISSIM simulation is the evaluation. The validation of a successful simulation run was based on running the simulation with the least errors and warnings possible for the entire time period set for the study. Once the simulation can be validated, charts are developed and the results can be exported to compare the MOEs.

CHAPTER IV

RESULTS AND DISCUSSION

4.1 Measurements of Efficiency (MOEs)

The MOEs that were considered to compare between SPUI and DDI include queue delay, queue length, vehicle delay, and stopped delay. In addition, the LOS from VISSIM help in selecting the ideal model. Before discussing the results, the simulation MOEs terms need to be defined and the level of service (LOS) since the methodology for this study is based on a microscopic simulation software. According to the PTV VISSIM user manual,

Table 4.1 was developed to define and summarize the terms needed from the simulation results.

Table 4.1 PTV VISSIM User Manual Results Description Evaluation MOE Description Results of terms Data collection Queue Total time in [s] that the vehicles have spent so far stuck measurements Delay in a queue, if the queue conditions are met. Queue Queue Maximum distance between the traffic counter and the counters length vehicle that meets the queue conditions defined. Average delay of all vehicles. Vehicle The delay of a vehicle in leaving a travel time Delay Delay measurement is obtained by subtracting the theoretical measurements (ideal) travel time from the actual travel time. Stopped Average stopped delay per vehicle in seconds without Delay stops at public transport stops and in parking lots. Level of service (transport quality): The levels of transport quality A to F for movements and edges, a density value (vehicle units/mile/lane). It is based on the Nodes LOS result attribute vehicle delay (average). The current value range of vehicle delay depends on the level of service scheme type of the node signalized or non-signalized.

The LOS in Vissim is comparable to the LOS defined in the American Highway Capacity Manual of 2010. Signalized intersection: LOS_A Loss time < 10 s or no volume, as no vehicle is moving, also due to traffic jam LOS_B > 10 s to 20 s LOS_C > 20 s to 35 s LOS_D > 35 s to 55 s LOS_E > 55 s to 80 s LOS_F > 80 s

Since SPUI and DDI operate differently, the weighted average of all the MOE results were calculated so the comparison would be reasonable (i.e., comparing apple to apples). The figures below show each MOE results for all models considered in the study.

In Figure 4.1, it is clear that the DDI queue delay was approximately 45% less than the

SPUI. Vehicles will be stuck in a queue for longer time in SPUIs design and that is not adequate in solving the congestion issue. In the existing CDI conditions, the queue delay of existing signal timing is 87% higher than the optimized single timing CDI.

Average Queue Delay 280 261 240

200

160

120

80 Weighted [s] Average 35 40 29 16 0 CDI SPUI DDI Existing CDI

Figure 4.1 Queue Delay Results

The results of the evaluation of queue counters is the queue length. SPUI had a maximum distance of about 42 ft for the queue length while DDI had 33 ft as seen in Figure

4.2. The optimized signal timing CDI model performed better than the existing signal timing CDI in regards to the queue length.

Average Queue Length 350 323 300

250

200

150

100

Weighted [ft] Average 63 42 50 33

0 CDI SPUI DDI Existing CDI

Figure 4.2 Queue Length Results

The results of the evaluation of delay measurements are vehicle delays and stopped delays. In Figure 4.3, the average vehicle delay in DDI was slightly higher than SPUI. The results of the average stopped delay per vehicle are shown in Figure 4.4. DDI had the lower value compared to SPUI although they differed only by 3 seconds. DDI performed better in the VISSIM simulation for the existing conditions as can been seen in most of the MOEs considered in this study.

Average Vehicle Delay 116 120

100

40 32

Weighted [s] Average 21 22 20

0 CDI SPUI DDI Existing CDI

Figure 4.3 Vehicle Delay Results

Average Stopped Delay 100 96 90 80 70 60 50 40 30 23 Weighted [s] Average 20 16 13 10 0 CDI SPUI DDI Existing CDI

Figure 4.4 Stopped Delay Results

4.2 Overall Level of Service (LOS) Comparison

The level of service for each model was found from the node results using VISSIM.

In both junction locations (1st and 2nd), a node was inserted for the CDIs and DDI models.

The existing signal timing CDI showed LOS E and D respectively. The optimized signal timing CDI gave a LOS C in both locations while the DDI showed a better LOS B in both locations. Since SPUI intersection network has only a single junction, at one LOS value, which in this case was C. Table 4.2 summarizes the LOS in all simulated models.

Table 4.2 VISSIM LOS Node Results Location Model 1st 2nd Existing CDI E D Modified CDI C C DDI B B SPUI C -

4.3 Known Advantages and Disadvantages of SPUI and DDI

4.3.1 The Single Point Urban Interchange

One of the advantages of the single point urban interchange is that it improves the operational efficiency as well as safety due to lower injury rates (Chlewicki, 2011). Also, it provides capacity for wider turns, thereby easing the movement of large vehicles such as trucks; SPUI also maximizes the traffic flow thus easing the congestion in urban areas

(Chlewicki, 2011). It has also led to better arterial coordination since the traffic going through the interchange can be controlled with one signal; SPUI is known to take less space compared to any other interchange which allows construction to take place on limited space. This minimizes the State’s use of eminent domain and overall access to business facilities in urban areas (Chlewicki, 2011).

On the flipside, SPUI has been shown to be costlier than any other interchange due to the construction of wider bridges and retaining walls (Bonneson, 1993). It is also confusing for drivers who are unfamiliar with the interchange since it has uncontrolled pavements in the middle of the interchange. Also, SPUI does not accommodate pedestrian facilities where they cannot get through the intersection with one green light (Bonneson,

1993). Furthermore, the SPUI makes it difficult to clear roads of snow due to the large area involved and ends up causing poor visibility. Drivers are not able to re-enter the freeway after departing since it only has left and right turns (Bonneson, 1993). The SPUI is also known to have poor placement of signal heads and confusing pavement markings in the interchange which leads to a long clearance between intervals in the interchange.

4.3.2 The Diverging Diamond Interchange

There are pros of the DDI which include the ability to increase the turning movement capacity to and from ramps (Sarangi, 2016). Besides, DDI has reduced off-road crashes due to the reduced horizontal curvature designed in the interchange. Moreover, it minimizes the conflicting points, thereby improving safety for the drivers (Sarangi, 2016).

It also increases the volume capacity of an existing underpass by reducing the need for turn lanes. Finally, the DDI improves the sight distance at turns as well as its construction

(Sarangi, 2016). In general, it reduces the risk of crashes by improving the flow of traffic and reducing the congestion at intersections (Sarangi, 2016).

On the other hand, the DDI requires buses driving through it to only stop outside the interchange which makes it rather inconvenient for both drivers as well as the passengers

(Dixon, 1997). The DDI is also quite risky for drivers who are not familiar with the interchange layout thereby making maneuvering difficult. Hence, big trucks cannot use the exit and ramps to bypass a bridge that is too low (Dixon, 1997). Also, it does not allow the existing traffic to re-enter the freeway in the same direction without first leaving the interchange since the signal cannot be green at both intersections when traffic is flowing in the same direction. This is only possible when the intersections are replaced with an underpass and pedestrians are forced to cross the interchange through free-flowing traffic which is quite dangerous (Dixon, 1997).

CHAPTER V

CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions

The comparison between the three interchange types CDI, SPUI, and DDI showed better simulation results for the DDI model in this study. Even after optimizing the signal timing for the CDI, the interchange needed improvements within the 2017 traffic volume data used. Adding more lanes might solve the congestion issue but safety is also what traffic engineers are mainly concerned about.

The current study compiled empirical results about CDIs, SPUIs, and DDIs from previous studies in order to determine which one among these would be the most effective in a real life scenario. The analysis shows a great amount of advantages and disadvantages, both from the points of view of SPUIs and DDIs.

It is true that SPUI is one of the most preferred system by the authorities across

United States because it is simply the best when it comes to efficiency and safety, two of the main considerations of drivers on the road, and the authorities as well. Additionally, as the number of vehicles and the size of vehicles increase, the need is increasing for such a design type. However, on the other hand, the cost of this interchange type acts as a significant barrier.

It is at such a juncture, that the use of DDI can be advocated. It is significantly less costly to implement, and due to the multiple signal point system, does not require too much

44 expertise to operate. Additionally, it incorporates many of the positive aspects of the SPUI, including a high amount of volume capacity, higher efficiency and safety, etc.

However, that does not make it the perfect method by any circumstances. It is difficult to maneuver for large vehicles like buses and trucks, and can also be difficult to operate for the drivers who do not have much experience in driving on these kind of interchanges because they are still very few in the country.

5.2 Recommendations

The current study recommends considering the pedestrian movement in the simulation. In addition to the spillback that might occur in the freeway and adjacent intersection. A good start before doing any simulation would be checking the signal timing.

Also, considering the morning peak hour data to see how the virtual models operate. The congestion issue might be solved within a new signal optimization without the necessity of changing the interchange design/type.

REFERENCES

Abatan, A., & Savolainen, P. T. (2018). Safety analysis of interchange functional

areas. Transportation Research Record, 2672(30), 120-130.

https://lib.dr.iastate.edu/etd/15479

Afshar, A. M., Bared, J. G., Wolf, S., & Edara, P. K. (2009). Traffic operational

comparison of single-point and diverging diamond interchanges (No. 09-2939).

Anderson, M., Schroer, B., & Moeller, D. (2012). Analyzing the diverging diamond

interchange using discrete event simulation. Modelling and Simulation in

Engineering, 2012, 47.

Bared, Joe, et al. “Crash Comparison of Single Point and Tight Diamond Interchanges.”

Journal of Transportation Engineering, 131(5), 2005, pp. 379-381.

Bared, J. G., Edara, P. K., & Jagannathan, R. (2005). Design and operational performance

of double crossover intersection and diverging diamond

interchange. Transportation Research Record, 1912(1), 31-38.

Bared, J. G., Granda, T., & Zineddin, A. (2007). Drivers' evaluation of the diverging

diamond interchange. Federal Highway Administration.

Bonneson, J. A. (1992). Operational Efficiency of the Single-Point Urban

Interchange. ITE Journal, 62(6).

Bonneson, J. A. (1993). Bridge size and clearance time of single-point urban

interchange. Journal of transportation engineering, 119(1), 77-93.

Chilukuri, V., Siromaskul, S., Trueblood, M., & Ryan, T. (2011). Diverging diamond

interchange performance evaluation (I-44 and Route 13) (No. OR11-012).

Missouri. Dept. of Transportation

Chlewicki, G. (2003). New interchange and intersection designs: The synchronized split-

phasing intersection and the diverging diamond interchange. In 2nd Urban Street

Symposium, Anaheim, California (pp. 28-30).

Chlewicki, G. (2011). Should the diverging diamond interchange always be considered a

diamond interchange form?. Transportation Research Record, 2223(1), 88-95.

Dixon, M. P. (1997). Calibrating and validating TRAF-NETSIM model of single-point

urban interchange. Transportation research record, 1591(1), 38-44.

Doctor, Mark, et al. Designing Complex Interchanges. US Department of Transportation

Federal Highway Administration. 2009. Retrieved from

https://www.fhwa.dot.gov/publications/publicroads/09novdec/01.cfm

Edara, P. K., Bared, J. G., & Jagannathan, R. (2005, June). Diverging Diamond

Interchange and Double Crossover Intersection-Vehicle and Pedestrian

Performance. In 3rd International Symposium on Highway Geometric Design,

Chicago, Ill.

Edara, P., Sun, C., Claros, B. R., & Brown, H. (2015). Safety evaluation of diverging

diamond interchanges in Missouri (No. cmr 15-006). Missouri. Dept. of

Transportation retrieved from https://www.modot.org/diamond-interchanges

Fang, F. C., & Elefteriadou, L. (2005). Some guidelines for selecting microsimulation

models for interchange traffic operational analysis. Journal of Transportation

Engineering, 131(7), 535-543.

Fowler, B. (1993). An operational comparison of the single-point urban and tight-

diamond interchanges. ITE journal, 64(4), 19-24.

Galletebeitia, B. (2011). Comparative analysis between the diverging diamond

interchange and partial cloverleaf interchange using microsimulation modeling.

Florida Atlantic University.

Garber, N. J., & Smith, M. J. (1996). Comparison of the operational and safety

characteristics of the single point urban and diamond interchanges (No.

FHWA/VA-97-R6). Virginia Transportation Research Council.

Garber, N. J., & Rivera, G. (2010). Safety performance functions for intersections on

highways maintained by the Virginia Department of Transportation (No. FHWA-

VTRC-11-CR1).Retrieved from https://safety.fhwa.dot.gov/intersection/

Hook, D. J. P., & Upchurch, J. O. N. A. T. H. A. N. (1992). Comparison of operational

parameters for conventional and single-point diamond

interchanges. Transportation Research Record, 1356, 47.

Hughes, W., Jagannathan, R., Sengupta, D., & Hummer, J. (2010). Alternative

intersections/interchanges: informational report (AIIR) (No. FHWA-HRT-09-

060). United States. Federal Highway Administration. Office of Research,

Development, and Technology.Retrieved from

https://www.fhwa.dot.gov/publications/research/safety/09060/09060.pdf

Hummer, J. E., Cunningham, C. M., Srinivasan, R., Warchol, S., Claros, B., Edara, P., &

Sun, C. (2016). Safety evaluation of seven of the earliest diverging diamond

interchanges installed in the United States. Transportation research

record, 2583(1), 25-33.

Hyatt, E., Griffin, R., Rue III, L. W., & McGwin Jr, G. (2009). The association between

price of regular-grade gasoline and injury and mortality rates among occupants

involved in motorcycle-and automobile-related motor vehicle collisions. Accident

Analysis & Prevention, 41(5), 1075-1079.Retrieved

from:https://www.bts.gov/content/number-us-aircraft-vehicles-vessels-and-other-

conveyances

Jones, E. G., & Selinger, M. J. (2003). Comparison of operations of single-point and tight

urban diamond interchanges. Transportation research record, 1847(1), 29-35.

Khan, T., & Anderson, M. (2016). Evaluating the Application of Diverging Diamond

Interchange in Athens, Alabama. International Journal for Traffic and Transport

Engineering, 6(1), 38-50.

Leisch, J. P., Urbanik, T. H. O. M. A. S., & Oxley, J. P. (1989). A comparison of two

diamond interchange forms in urban areas. ITE journal, 5(59), 21-27.

Lloyd, H. (2016). A Comprehensive Safety Analysis of Diverging Diamond

Interchanges.

Loveland, J. E., Taylor, J. C., Lewis, J. D., Childs, B. M., Reed, C. D., & Robertson, J.

W. (2016). U.S. Patent No. 9,501,700. Washington, DC: U.S. Patent and

Trademark Office. Retrieved from

http://www.dot.state.oh.us/Divisions/Engineering/Roadway/studies/IOS%20Exam

ples/MOT-I-75-0.76;%20PID%2099213.pdf

Maerz, N. H., Youssef, A., & Fennessey, T. W. (2005). New risk–consequence rockfall

hazard rating system for Missouri highways using digital image

analysis. Environmental & Engineering Geoscience, 11(3), 229-249.Retrieved

from https://www.modot.org/highway-features-0

Poppe, M. J., Radwan, A. E., & Matthias, J. S. (1991). Some traffic parameters for the

evaluation of the single-point diamond interchange (No. 1303).

Qureshi, M., Spring, G., Lasod, R., & Sugathan, N. (2004). Design of single point urban

interchanges (No. RDT 04-011,).Retrieved from https://www.modot.org/single-

point-urban-interchanges

Radwan, A. E., & Hatton, R. L. (1990). Evaluation tools of urban interchange design and

operation. Transportation Research Record, (1280).

Sarangi, Ashis K. "Diverging Diamond Interchange." IOSR Journal of Mechanical and

Civil Engineering, vol. 13, no. 05, 2016, pp. 32-40.

Schroeder, B. J., Salamati, K., & Hummer, J. (2014). Calibration and field validation of

four double-crossover diamond interchanges in VISSIM

microsimulation. Transportation Research Record, 2404(1), 49-58.

Sharma, S., & Chatterjee, I. (2007, November). Performance evaluation of the diverging

diamond interchange in comparison with the conventional diamond interchange.

In Transportation Scholars Conference, Iowa State University, Ames.

Siromaskul, Smith. “Breaking the Diamond: DDIs, CFIs, and SPUIs.” Western ITE,

2011, pp. 1-11. Retrieved from https://westernite.org/awards/bestpaper/2011-

Siromaskul.pdf

Smith, M. J., & Garber, N. J. (1998). Guidelines for selecting single-point urban and

diamond interchanges: Nationwide survey and literature review. Transportation

research record, 1612(1), 48-54.

Song, H., & Yang, X. (2012). Comparison of Operation Performance of Diamond

Interchanges between China and USA. Procedia-Social and Behavioral

Sciences, 43, 125-134.

Tarko, A. P., Romero, M. A., & Sultana, A. (2017). Performance of Alternative Diamond

Interchange Forms: Volume 1.Retrieved from

https://doi.org/10.5703/1288284316385

Torbic, D. J., Harwood, D. W., Gilmore, D. K., & Richard, K. R. (2007). Interchange

safety analysis tool (isat): User manual(No. FHWA-HRT-07-045). Turner-

Fairbank Highway Research Center.

Yang, X., Chang, G. L., & Rahwanji, S. (2014). Development of a signal optimization

model for diverging diamond interchange. Journal of Transportation

Engineering, 140(5), 04014010.Retrieved from

https://safety.fhwa.dot.gov/intersection/innovative/crossover/brochures/ddi/

Zhao, L., Malikopoulos, A. A., & Rios-Torres, J. (2019). On the Traffic Impacts of

Optimally Controlled Connected and Automated Vehicles. arXiv preprint

arXiv:1903.03459.

APPENDIX A

SPUI 12/05/2017 Volume Data

Passenger Cars and trucks pm % SB R 301 20 L 1210 80 total 1511

NB R 561 71 L 232 29 total 793

EB R 175 23 Thru 327 43 L 256 34 total 758

WB R 1029 49 Thru 444 21 L 608 29 total 2081