With the rapid changes in land use development along suburban arterials in Shanghai, there is als... more With the rapid changes in land use development along suburban arterials in Shanghai, there is also a corresponding increase in traffic demand along these arterials. With a preference toward increased accessibility and efficiency, these arterials have been installed with an increased number of signalized intersections and accesses to serve local traffic needs. The absence of a defined functional hierarchy along the road network, together with the non-uniform installation of signals and accesses tends to deteriorate arterial safety. Previous studies on arterial safety have generally been based on a single type of road entity (either intersection or roadway segment). These studies only analyzed partial safety impacts of signal spacing and access density, as these factors would significantly influence the safety performance of both intersections and roadway segments. Macro level safety modeling was usually applied to investigate the relationship between the zonal crash frequencies and demographics, road network features and traffic characteristics. In this study, a new modeling strategy was proposed to analyze the safety impacts of roadway network features (i.e., road network patterns, signal spacing and access density) of arterials by applying a macro level safety modeling technique. Bayesian Conditional Autoregressive models were developed for arterials covering 173 Traffic Analysis Zones in the suburban area in Shanghai. The results identified that the road network pattern with collector roads parallel to the arterials was shown to be associated with fewer crashes than those without parallel collectors. Higher signal density and access density also tended to increase crash frequencies on arterials.
BRIGHAM YOUNG UNIVERSITY As chair of the candidate's graduate committee, I have read the thesis o... more BRIGHAM YOUNG UNIVERSITY As chair of the candidate's graduate committee, I have read the thesis of Aaron Paul Jensen in its final form and have found that (1) its format, citations, and bibliographical style are consistent and acceptable and fulfill university and department style requirements; (2) its illustrative materials including figures, tables, and charts are in place; and (3) the final manuscript is satisfactory to the graduate committee and is ready for submission to the university library. Date Grant G. Schultz Chair, Graduate Committee
The collection and interpretation of data is a critical component of traffic and transportation e... more The collection and interpretation of data is a critical component of traffic and transportation engineering used to establish baseline performance measures and to forecast future conditions. One important source of traffic data is commercial motor vehicle (CMV) weight and classification data used as input to critical tasks in transportation design, operations, and planning. The evolution of Intelligent Transportation System (ITS) technologies has been providing transportation engineers and planners with an increased availability of CMV data. The primary sources of these data are automatic vehicle classification (AVC) and weigh-in-motion (WIM). Microscopic traffic simulation models have been used extensively to model the dynamic and stochastic nature of transportation systems including vehicle composition. One aspect of The majority of the value of trade that occurs between the United States, Mexico, and Canada is delivered between the three countries through the use of the highway network. The U.S. Department of Transportation (USDOT), Bureau of Transportation Statistics (BTS) reported that in 1999 trucks transported approximately 69 percent of the value of NAFTA merchandise trade, rail transported approximately 14 percent of the share, and air and water modes accounted for approximately 4 to 6 percent (10). More specifically, truck traffic has increased substantially since the implementation of NAFTA, particularly at United States border crossing locations with both Canada and Mexico. In the state of Texas, for example, total truck crossings into Mexico from Texas have increased from 974,017 in 1993 to 2,184,441 in 2001, an overall increase of 124 percent (11). Total truck crossings into Texas from Mexico have also increased during this time from 509,477 in 1993 to 2,239,313 in 2001, an overall increase of 340 percent (12). During the same time as truck crossings were increasing, vehicles crossings into
With rapid changes in land use development along suburban arterials in Shanghai, there is a corre... more With rapid changes in land use development along suburban arterials in Shanghai, there is a corresponding increase in traffic demand on these arterials. To accommodate the local traffic needs of high accessibility and efficiency, an increased number of signalized intersections and accesses have been installed. However, the absence of a defined hierarchical road network, together with irregular signal spacing and access density, tends to deteriorate arterial safety. Previous studies on arterial safety were generally based on a single type of road entity, either intersection or roadway segment, and they analyzed the safety contributing factors (e.g. signal density and access density) on only that type of road entity, while these suburban arterial characteristics could significantly influence the safety performance of both intersections and roadway segments. Macro-level safety modeling was usually applied to investigate the relationships between zonal crash frequencies and demographics, road network features, and traffic characteristics, but the previous researchers did not consider the specific arterial characteristics of signal density and access density. In this study, a new modeling strategy was proposed to analyze the safety impacts of zonal roadway network features (i.e., road network patterns and road network density) along with the suburban arterial characteristics of signal density and access density. Bayesian Conditional Autoregressive Poisson Log-normal models were developed for suburban arterials in 173 traffic analysis zones in the suburban area of Shanghai. Results identified that the grid pattern road network with collector roads parallel to arterials was associated with fewer crashes than networks without parallel collectors. On the other hand, lower road network density, higher signal density and higher access density tended to increase the crash occurrence on suburban arterials.
Transportation Research Board 89th Annual MeetingTransportation Research Board, 2010
BRIGHAM YOUNG UNIVERSITY As chair of the candidate's graduate committee, I have read the thesis o... more BRIGHAM YOUNG UNIVERSITY As chair of the candidate's graduate committee, I have read the thesis of Katherine E. Winters in its final form and have found that (1) its format, citations, and bibliographical style are consistent and acceptable and fulfill university and department style requirements; (2) its illustrative materials including figures, tables, and charts are in place; and (3) the final manuscript is satisfactory to the graduate committee and is ready for submission to the university library. Date Grant G. Schultz Chair, Graduate Committee
ITE 2007 Annual Meeting and ExhibitInstitute of Transportation Engineers (ITE), 2007
Page 1. Evaluating the Impact of Raised Median Installations Grant G. Schultz, Ph.D., PE, PTOE; J... more Page 1. Evaluating the Impact of Raised Median Installations Grant G. Schultz, Ph.D., PE, PTOE; Jeff S. Lewis, EIT, Tim Boschert Abstract: Traffic volumes and congestion across the state of Utah and the throughout the nation ...
Raised medians offer a departure from more traditional two-way left turn lanes typically built on... more Raised medians offer a departure from more traditional two-way left turn lanes typically built on collector and arterial streets and can offer advantages in terms of safety, capacity, and aesthetics. At the same time, individual business owners often oppose raised medians due to fear of business loss. This paper summarizes research on the effects of raised medians on retail sales in Utah before and after the installation of raised medians. Sales analysis was also performed for corresponding control corridors in which a similar roadway project was completed that did not include the installation of a raised median. For all of the corridors in which raised medians were constructed, there was an increase in corridor-area retail sales and sales per square foot. Analysis showed that in every case there was no evidence of a negative impact on corridor sales due to the raised median installation. A business impact survey was administrated to qualitatively evaluate the perceived impacts of each road project in front of individual businesses. Business owners on corridors, where the project included the installation of a raised median, typically perceived the actual results of the project more negatively than corridors, where the project did not install a raised median.
Transportation research interdisciplinary perspectives, Nov 1, 2020
One common challenge of modeling intersection related crash data is the high proportion of sites ... more One common challenge of modeling intersection related crash data is the high proportion of sites with zero crashes. Extensive research has been done on appropriate methods to handle excess zeroes. There is some reluctance to use zero-inflated models in the traffic safety literature. The primary purpose of this paper is to evaluate zero-inflated models to determine if they are a suitable method for modeling crash counts. An appropriate approach to model selection is to choose the model that best accomplishes research objectives rather than attempting to discover the true underlying data generating process. Thus using zero-inflated models is warranted when they outperform other models relative to research objectives. In addition, using zero-inflated models does not assume sites are in an inherently safe or unsafe state, and should not be summarily dismissed on the basis of disagreement with the hypothesized underlying data generating process. Secondarily, we compare implementations of zero-inflated Poisson, zero-inflated negative binomial, and negative binomial-Lindley Bayesian hierarchical models using intersection related crash data for the state of Utah from 2014 to 2018. We specifically compare the quality of fit as determined by a Bayesian χ 2 test for goodness-of-fit and their relative predictive accuracy. The zero-inflated negative binomial performs best overall. We conclude that there are cases where zero-inflated models perform as well or better than other comparable models and may be considered as a viable option to model crash counts.
Traffic volumes and congestion continue to increase on arterial roads. As such the safety and per... more Traffic volumes and congestion continue to increase on arterial roads. As such the safety and performance of these roads is a continual concern. Transportation systems must be evaluated on an ongoing basis to ensure that people and goods can be moved as efficiently and safely as possible. Safety and performance indices provide a method to numerically measure given data about a system so that comparisons and rankings on safety and performance can be made as objectively as possible. One of the sets of tools that have proven successful in improving the safety and efficiency of arterial roads are access management techniques. To determine which roads can most benefit by the implementation of access management techniques, a prioritization process was developed to guide decision makers in the implementation process. Recommendations were given in the form of a decision tree classifying existing or future road segments into subcategories based on volume, signal spacing, adjacent land use, and other criteria. The objective of this paper is to document the steps followed to develop the prioritization process based on principles of performance indices that can be utilized to target arterial roads that would benefit from access management techniques and principles. Utilizing the results of the research, decision makers can better determine which sections of roadway can benefit from controlling driveway access, installing raised medians, providing future planning, or looking to a solution other than access management.
Journal of transportation engineering, Feb 1, 2010
Relationship between Access Management and Other Physical Roadway Characteristics and Safety. [Jo... more Relationship between Access Management and Other Physical Roadway Characteristics and Safety. [Journal of Transportation Engineering 136, 141 (2010)]. Grant G. Schultz, Ph.D., PE, PTOE, M.ASCE, Kordel T. Braley, EIT, Tim Boschert. Abstract. ...
The intersections of major arterials are designed to facilitate the conflicting movements of nume... more The intersections of major arterials are designed to facilitate the conflicting movements of numerous vehicles in a manner that is both safe and efficient. Accesses located within the functional area of major arterial intersections complicate intersection activity because additional conflicts arise from ingressing and egressing movements at the accesses. This research analyzed the impact of accesses on crashes within the functional area of major arterials. The effects of access spacing within functional areas and access setback from intersections were addressed. The functional areas of 144 signalized major arterial intersections across the state of Utah were examined. A database was developed and contained the frequency, type, and severity of functional area crashes as well as the intersection and roadway characteristics within the functional area. Statistical analyses were conducted to determine the influence of accesses on crashes within the functional area of intersections. The statistical analyses showed that the existence of accesses within the functional area was correlated with increased crashes and crash severity costs. In particular, an increase in commercial access density was associated with increases in crash totals, crash rates, and rear-end crashes in intersection functional areas. The analyses also showed that study intersections meeting Utah Department of Transportation corner clearance standards exhibited fewer right-angle crashes and lower crash severity costs. Adherence to such standards improves safety and increases efficiency of the transportation network and thus aids jurisdictions throughout the nation in making the most of the existing infrastructure.
As motorists approach high-speed signalized intersections (HSSIs), they are often faced with a di... more As motorists approach high-speed signalized intersections (HSSIs), they are often faced with a dilemma as signal indications turn yellow, and subsequently red. This dilemma may exist due to inadequate signal timing (dilemma zone) or due to the variability in response times and driving habits of motorists (decision zone). One alternative to aid in eliminating, or reducing, this dilemma is the installation of an advance warning signal (AWS) in conjunction with advanced detection technology to reduce the probability that a motorist will be caught in a dilemma, while providing advance warning of impending signal changes to aid the motorist in the decision making process. In 2005, the Utah Department of Transportation installed dynamic AWS systems upstream of four HSSIs in Salt Lake County. These installations included a blank-out sign with the message “Prepare To Stop” activated in advance of the yellow indication. The installation at the intersection of Bangerter Highway and 13400 South was evaluated for a period of two years after installation. The metrics evaluated included crash data, speed distributions, and red-light running (RLR). The results of the analysis showed that the installation of the AWS system helped to reduce overall speeds just prior to the onset of the yellow change interval, while slightly reducing the overall rate and frequency of crashes. RLR results, however, were mixed with rates rising and falling throughout the study. The purpose of this paper is to briefly summarize the results of the final chapter of the research while providing references to the full results.
Transportation Frontiers for the Next Millennium: 69th Annual Meeting of the Institute of Transportation EngineersInstitute of Transportation Engineers (ITE), 1999
As the state capital and largest metropolitan area in Utah, Salt Lake City is the center of trans... more As the state capital and largest metropolitan area in Utah, Salt Lake City is the center of transportation activity along the Wasatch Front. An increase in vehicles of 70% is predicted for the Salt Lake Urbanized Area between 1995 and 2020. Regional long range planning along the Wasatch Front has confirmed the need for additional intercity mass transit. As a result, an environmental assessment (EA) and site selection process was begun in early 1997. The EA process was instrumental in establishing the purpose and need for the Salt Lake City Intermodal Center, determining the location of the center and providing a description of the uses intended at the center. Based on the results of the EA, recommendations were made to the Federal Transit Administration; while all through the process, many valuable lessons were learned by the city and its consultants.
With the rapid changes in land use development along suburban arterials in Shanghai, there is als... more With the rapid changes in land use development along suburban arterials in Shanghai, there is also a corresponding increase in traffic demand along these arterials. With a preference toward increased accessibility and efficiency, these arterials have been installed with an increased number of signalized intersections and accesses to serve local traffic needs. The absence of a defined functional hierarchy along the road network, together with the non-uniform installation of signals and accesses tends to deteriorate arterial safety. Previous studies on arterial safety have generally been based on a single type of road entity (either intersection or roadway segment). These studies only analyzed partial safety impacts of signal spacing and access density, as these factors would significantly influence the safety performance of both intersections and roadway segments. Macro level safety modeling was usually applied to investigate the relationship between the zonal crash frequencies and demographics, road network features and traffic characteristics. In this study, a new modeling strategy was proposed to analyze the safety impacts of roadway network features (i.e., road network patterns, signal spacing and access density) of arterials by applying a macro level safety modeling technique. Bayesian Conditional Autoregressive models were developed for arterials covering 173 Traffic Analysis Zones in the suburban area in Shanghai. The results identified that the road network pattern with collector roads parallel to the arterials was shown to be associated with fewer crashes than those without parallel collectors. Higher signal density and access density also tended to increase crash frequencies on arterials.
Access management, defined in the Transportation Research Board Access Management Manual as "the ... more Access management, defined in the Transportation Research Board Access Management Manual as "the systematic control of the location, spacing, design, and operation of driveways, median openings, interchanges, and street connections to a roadway," has been shown to have a positive impact on roadway safety. Numerous studies have been conducted on the safety relationship of access management techniques as a function of access spacing, corner clearance, and medians. Several of these studies have been conducted in the United States, including studies completed in the state of Utah. The results of research performed at Brigham Young University for the Utah Department of Transportation are highlighted in this paper. Specific research includes raised median safety impacts from both a traditional analysis methodology and using Bayesian methods, as well as an analysis of access management techniques (e.g., corner clearance, access spacing, median openings, left-turn lanes, etc.) at major-arterial intersections. The purpose of the paper is to present an overview on the safety impacts of access management identified, while providing the necessary references to allow the reader to review details and specific analysis results of these and other safety studies. The results of the analyses indicate that access management techniques play a role in improving and maintaining safety along urban and suburban arterials and at major-arterial intersections in the state of Utah. Access management has, and will continue to, improve safety when implemented appropriately. Agencies across the world should identify how access management can best be implemented in their jurisdictions and apply these principles.
This report documents the first-year effort of a research project that provides recommendations f... more This report documents the first-year effort of a research project that provides recommendations for the use of access management techniques on state roadways in Texas. In the first year of the project, the research team focused on developing a matrix of guidelines for the application of different access management techniques for various roadway access classifications. The access management treatments for which recommended guidelines are presented include minimum access spacing, minimum corner clearance, median treatments, auxiliary lanes, alternate left-turn treatments, access separation at interchanges, frontage roads, and the use of traffic impact analyses for site development. The matrix allows the user to identify critical threshold criteria for the application of each access management technique, given the projected roadway access classification. The guidelines presented in this report will be valuable for state transportation professionals for use on new and retrofit projects as a toolbox of techniques for managing access to all state roadways-thus preserving the intended use of these facilities.
BRIGHAM YOUNG UNIVERSITY As chair of the candidate's graduate committee, I have read the thesis o... more BRIGHAM YOUNG UNIVERSITY As chair of the candidate's graduate committee, I have read the thesis of Jeff S. Lewis in its final form and have found that (1) its format, citations, and bibliographical style are consistent and acceptable and fulfill university and department style requirements; (2) its illustrative materials including figures, tables, and charts are in place; and (3) the final manuscript is satisfactory to the graduate committee and is ready for submission to the university library. Date Grant G. Schultz Chair, Graduate Committee
A driver approaching a signalized intersection where the light has turned yellow must make a deci... more A driver approaching a signalized intersection where the light has turned yellow must make a decision whether to stop or proceed. A signal that is properly designed will provide an opportunity for a safe and legal maneuver. As approach speeds increase, however, it becomes more difficult to execute a safe maneuver. One countermeasure that is used to help provide advance warning to drivers of an approaching intersection or the impending signal change at an approaching intersection is an advance warning signal (AWS) system. A number of AWS systems have been installed throughout the country. Four such systems were installed in the state of Utah in 2005. Since that time the effectiveness of these systems has been evaluated as a function of intersection safety. The metrics used for evaluation include crash data analysis, speed distribution analysis, and red-light running (RLR) analysis. The objective of this study is to evaluate and report the long-term effectiveness of the AWS systems installed in the state of Utah in June 2005, particularly at the intersection of Bangerter Highway and 13400 South. The results of the study indicate that overall the AWS system has generally had a positive impact on the community, with positive results noted in all areas of analysis. Given the nature of the study, however, it is difficult to quantify the extent of the overall impact as a function of only the AWS system.
Crash data are key components in transportation safety studies. In recent research completed by B... more Crash data are key components in transportation safety studies. In recent research completed by Brigham Young University (BYU) for the Utah Department of Transportation (UDOT), crash data were evaluated for 175 segments of 49 different state routes for a total of 207 miles of arterial roadway. Included in the crash dataset were the results of over 28,800 crashes aggregated by severity and collision type utilizing the UDOT web-based crash data almanac. The crash data almanac allows users to search reported crash data and establish filters for quick evaluation of results. In the research completed by BYU, crash data were evaluated to determine which characteristics of roadway sections were related to safety including crash rate, crash severity, and collision type. To accomplish this objective, several methodologies were developed to calculate crash severity scores, while the data almanac was utilized to collect crash rates and collision type data. The objective of this paper is to summarize the crash data collection process for this and other studies and to outline ways in which crash data can be useful in evaluating transportation safety. The specific application in this research is that of access management and the relationship between roadway characteristics and access management techniques. The results of this paper are expected to provide direction and guidance to engineers and planners on the use of crash data, specifically searchable crash databases, while also identifying the safety benefits of access management techniques based on the relationships between such techniques and crash histories.
With the rapid changes in land use development along suburban arterials in Shanghai, there is als... more With the rapid changes in land use development along suburban arterials in Shanghai, there is also a corresponding increase in traffic demand along these arterials. With a preference toward increased accessibility and efficiency, these arterials have been installed with an increased number of signalized intersections and accesses to serve local traffic needs. The absence of a defined functional hierarchy along the road network, together with the non-uniform installation of signals and accesses tends to deteriorate arterial safety. Previous studies on arterial safety have generally been based on a single type of road entity (either intersection or roadway segment). These studies only analyzed partial safety impacts of signal spacing and access density, as these factors would significantly influence the safety performance of both intersections and roadway segments. Macro level safety modeling was usually applied to investigate the relationship between the zonal crash frequencies and demographics, road network features and traffic characteristics. In this study, a new modeling strategy was proposed to analyze the safety impacts of roadway network features (i.e., road network patterns, signal spacing and access density) of arterials by applying a macro level safety modeling technique. Bayesian Conditional Autoregressive models were developed for arterials covering 173 Traffic Analysis Zones in the suburban area in Shanghai. The results identified that the road network pattern with collector roads parallel to the arterials was shown to be associated with fewer crashes than those without parallel collectors. Higher signal density and access density also tended to increase crash frequencies on arterials.
BRIGHAM YOUNG UNIVERSITY As chair of the candidate's graduate committee, I have read the thesis o... more BRIGHAM YOUNG UNIVERSITY As chair of the candidate's graduate committee, I have read the thesis of Aaron Paul Jensen in its final form and have found that (1) its format, citations, and bibliographical style are consistent and acceptable and fulfill university and department style requirements; (2) its illustrative materials including figures, tables, and charts are in place; and (3) the final manuscript is satisfactory to the graduate committee and is ready for submission to the university library. Date Grant G. Schultz Chair, Graduate Committee
The collection and interpretation of data is a critical component of traffic and transportation e... more The collection and interpretation of data is a critical component of traffic and transportation engineering used to establish baseline performance measures and to forecast future conditions. One important source of traffic data is commercial motor vehicle (CMV) weight and classification data used as input to critical tasks in transportation design, operations, and planning. The evolution of Intelligent Transportation System (ITS) technologies has been providing transportation engineers and planners with an increased availability of CMV data. The primary sources of these data are automatic vehicle classification (AVC) and weigh-in-motion (WIM). Microscopic traffic simulation models have been used extensively to model the dynamic and stochastic nature of transportation systems including vehicle composition. One aspect of The majority of the value of trade that occurs between the United States, Mexico, and Canada is delivered between the three countries through the use of the highway network. The U.S. Department of Transportation (USDOT), Bureau of Transportation Statistics (BTS) reported that in 1999 trucks transported approximately 69 percent of the value of NAFTA merchandise trade, rail transported approximately 14 percent of the share, and air and water modes accounted for approximately 4 to 6 percent (10). More specifically, truck traffic has increased substantially since the implementation of NAFTA, particularly at United States border crossing locations with both Canada and Mexico. In the state of Texas, for example, total truck crossings into Mexico from Texas have increased from 974,017 in 1993 to 2,184,441 in 2001, an overall increase of 124 percent (11). Total truck crossings into Texas from Mexico have also increased during this time from 509,477 in 1993 to 2,239,313 in 2001, an overall increase of 340 percent (12). During the same time as truck crossings were increasing, vehicles crossings into
With rapid changes in land use development along suburban arterials in Shanghai, there is a corre... more With rapid changes in land use development along suburban arterials in Shanghai, there is a corresponding increase in traffic demand on these arterials. To accommodate the local traffic needs of high accessibility and efficiency, an increased number of signalized intersections and accesses have been installed. However, the absence of a defined hierarchical road network, together with irregular signal spacing and access density, tends to deteriorate arterial safety. Previous studies on arterial safety were generally based on a single type of road entity, either intersection or roadway segment, and they analyzed the safety contributing factors (e.g. signal density and access density) on only that type of road entity, while these suburban arterial characteristics could significantly influence the safety performance of both intersections and roadway segments. Macro-level safety modeling was usually applied to investigate the relationships between zonal crash frequencies and demographics, road network features, and traffic characteristics, but the previous researchers did not consider the specific arterial characteristics of signal density and access density. In this study, a new modeling strategy was proposed to analyze the safety impacts of zonal roadway network features (i.e., road network patterns and road network density) along with the suburban arterial characteristics of signal density and access density. Bayesian Conditional Autoregressive Poisson Log-normal models were developed for suburban arterials in 173 traffic analysis zones in the suburban area of Shanghai. Results identified that the grid pattern road network with collector roads parallel to arterials was associated with fewer crashes than networks without parallel collectors. On the other hand, lower road network density, higher signal density and higher access density tended to increase the crash occurrence on suburban arterials.
Transportation Research Board 89th Annual MeetingTransportation Research Board, 2010
BRIGHAM YOUNG UNIVERSITY As chair of the candidate's graduate committee, I have read the thesis o... more BRIGHAM YOUNG UNIVERSITY As chair of the candidate's graduate committee, I have read the thesis of Katherine E. Winters in its final form and have found that (1) its format, citations, and bibliographical style are consistent and acceptable and fulfill university and department style requirements; (2) its illustrative materials including figures, tables, and charts are in place; and (3) the final manuscript is satisfactory to the graduate committee and is ready for submission to the university library. Date Grant G. Schultz Chair, Graduate Committee
ITE 2007 Annual Meeting and ExhibitInstitute of Transportation Engineers (ITE), 2007
Page 1. Evaluating the Impact of Raised Median Installations Grant G. Schultz, Ph.D., PE, PTOE; J... more Page 1. Evaluating the Impact of Raised Median Installations Grant G. Schultz, Ph.D., PE, PTOE; Jeff S. Lewis, EIT, Tim Boschert Abstract: Traffic volumes and congestion across the state of Utah and the throughout the nation ...
Raised medians offer a departure from more traditional two-way left turn lanes typically built on... more Raised medians offer a departure from more traditional two-way left turn lanes typically built on collector and arterial streets and can offer advantages in terms of safety, capacity, and aesthetics. At the same time, individual business owners often oppose raised medians due to fear of business loss. This paper summarizes research on the effects of raised medians on retail sales in Utah before and after the installation of raised medians. Sales analysis was also performed for corresponding control corridors in which a similar roadway project was completed that did not include the installation of a raised median. For all of the corridors in which raised medians were constructed, there was an increase in corridor-area retail sales and sales per square foot. Analysis showed that in every case there was no evidence of a negative impact on corridor sales due to the raised median installation. A business impact survey was administrated to qualitatively evaluate the perceived impacts of each road project in front of individual businesses. Business owners on corridors, where the project included the installation of a raised median, typically perceived the actual results of the project more negatively than corridors, where the project did not install a raised median.
Transportation research interdisciplinary perspectives, Nov 1, 2020
One common challenge of modeling intersection related crash data is the high proportion of sites ... more One common challenge of modeling intersection related crash data is the high proportion of sites with zero crashes. Extensive research has been done on appropriate methods to handle excess zeroes. There is some reluctance to use zero-inflated models in the traffic safety literature. The primary purpose of this paper is to evaluate zero-inflated models to determine if they are a suitable method for modeling crash counts. An appropriate approach to model selection is to choose the model that best accomplishes research objectives rather than attempting to discover the true underlying data generating process. Thus using zero-inflated models is warranted when they outperform other models relative to research objectives. In addition, using zero-inflated models does not assume sites are in an inherently safe or unsafe state, and should not be summarily dismissed on the basis of disagreement with the hypothesized underlying data generating process. Secondarily, we compare implementations of zero-inflated Poisson, zero-inflated negative binomial, and negative binomial-Lindley Bayesian hierarchical models using intersection related crash data for the state of Utah from 2014 to 2018. We specifically compare the quality of fit as determined by a Bayesian χ 2 test for goodness-of-fit and their relative predictive accuracy. The zero-inflated negative binomial performs best overall. We conclude that there are cases where zero-inflated models perform as well or better than other comparable models and may be considered as a viable option to model crash counts.
Traffic volumes and congestion continue to increase on arterial roads. As such the safety and per... more Traffic volumes and congestion continue to increase on arterial roads. As such the safety and performance of these roads is a continual concern. Transportation systems must be evaluated on an ongoing basis to ensure that people and goods can be moved as efficiently and safely as possible. Safety and performance indices provide a method to numerically measure given data about a system so that comparisons and rankings on safety and performance can be made as objectively as possible. One of the sets of tools that have proven successful in improving the safety and efficiency of arterial roads are access management techniques. To determine which roads can most benefit by the implementation of access management techniques, a prioritization process was developed to guide decision makers in the implementation process. Recommendations were given in the form of a decision tree classifying existing or future road segments into subcategories based on volume, signal spacing, adjacent land use, and other criteria. The objective of this paper is to document the steps followed to develop the prioritization process based on principles of performance indices that can be utilized to target arterial roads that would benefit from access management techniques and principles. Utilizing the results of the research, decision makers can better determine which sections of roadway can benefit from controlling driveway access, installing raised medians, providing future planning, or looking to a solution other than access management.
Journal of transportation engineering, Feb 1, 2010
Relationship between Access Management and Other Physical Roadway Characteristics and Safety. [Jo... more Relationship between Access Management and Other Physical Roadway Characteristics and Safety. [Journal of Transportation Engineering 136, 141 (2010)]. Grant G. Schultz, Ph.D., PE, PTOE, M.ASCE, Kordel T. Braley, EIT, Tim Boschert. Abstract. ...
The intersections of major arterials are designed to facilitate the conflicting movements of nume... more The intersections of major arterials are designed to facilitate the conflicting movements of numerous vehicles in a manner that is both safe and efficient. Accesses located within the functional area of major arterial intersections complicate intersection activity because additional conflicts arise from ingressing and egressing movements at the accesses. This research analyzed the impact of accesses on crashes within the functional area of major arterials. The effects of access spacing within functional areas and access setback from intersections were addressed. The functional areas of 144 signalized major arterial intersections across the state of Utah were examined. A database was developed and contained the frequency, type, and severity of functional area crashes as well as the intersection and roadway characteristics within the functional area. Statistical analyses were conducted to determine the influence of accesses on crashes within the functional area of intersections. The statistical analyses showed that the existence of accesses within the functional area was correlated with increased crashes and crash severity costs. In particular, an increase in commercial access density was associated with increases in crash totals, crash rates, and rear-end crashes in intersection functional areas. The analyses also showed that study intersections meeting Utah Department of Transportation corner clearance standards exhibited fewer right-angle crashes and lower crash severity costs. Adherence to such standards improves safety and increases efficiency of the transportation network and thus aids jurisdictions throughout the nation in making the most of the existing infrastructure.
As motorists approach high-speed signalized intersections (HSSIs), they are often faced with a di... more As motorists approach high-speed signalized intersections (HSSIs), they are often faced with a dilemma as signal indications turn yellow, and subsequently red. This dilemma may exist due to inadequate signal timing (dilemma zone) or due to the variability in response times and driving habits of motorists (decision zone). One alternative to aid in eliminating, or reducing, this dilemma is the installation of an advance warning signal (AWS) in conjunction with advanced detection technology to reduce the probability that a motorist will be caught in a dilemma, while providing advance warning of impending signal changes to aid the motorist in the decision making process. In 2005, the Utah Department of Transportation installed dynamic AWS systems upstream of four HSSIs in Salt Lake County. These installations included a blank-out sign with the message “Prepare To Stop” activated in advance of the yellow indication. The installation at the intersection of Bangerter Highway and 13400 South was evaluated for a period of two years after installation. The metrics evaluated included crash data, speed distributions, and red-light running (RLR). The results of the analysis showed that the installation of the AWS system helped to reduce overall speeds just prior to the onset of the yellow change interval, while slightly reducing the overall rate and frequency of crashes. RLR results, however, were mixed with rates rising and falling throughout the study. The purpose of this paper is to briefly summarize the results of the final chapter of the research while providing references to the full results.
Transportation Frontiers for the Next Millennium: 69th Annual Meeting of the Institute of Transportation EngineersInstitute of Transportation Engineers (ITE), 1999
As the state capital and largest metropolitan area in Utah, Salt Lake City is the center of trans... more As the state capital and largest metropolitan area in Utah, Salt Lake City is the center of transportation activity along the Wasatch Front. An increase in vehicles of 70% is predicted for the Salt Lake Urbanized Area between 1995 and 2020. Regional long range planning along the Wasatch Front has confirmed the need for additional intercity mass transit. As a result, an environmental assessment (EA) and site selection process was begun in early 1997. The EA process was instrumental in establishing the purpose and need for the Salt Lake City Intermodal Center, determining the location of the center and providing a description of the uses intended at the center. Based on the results of the EA, recommendations were made to the Federal Transit Administration; while all through the process, many valuable lessons were learned by the city and its consultants.
With the rapid changes in land use development along suburban arterials in Shanghai, there is als... more With the rapid changes in land use development along suburban arterials in Shanghai, there is also a corresponding increase in traffic demand along these arterials. With a preference toward increased accessibility and efficiency, these arterials have been installed with an increased number of signalized intersections and accesses to serve local traffic needs. The absence of a defined functional hierarchy along the road network, together with the non-uniform installation of signals and accesses tends to deteriorate arterial safety. Previous studies on arterial safety have generally been based on a single type of road entity (either intersection or roadway segment). These studies only analyzed partial safety impacts of signal spacing and access density, as these factors would significantly influence the safety performance of both intersections and roadway segments. Macro level safety modeling was usually applied to investigate the relationship between the zonal crash frequencies and demographics, road network features and traffic characteristics. In this study, a new modeling strategy was proposed to analyze the safety impacts of roadway network features (i.e., road network patterns, signal spacing and access density) of arterials by applying a macro level safety modeling technique. Bayesian Conditional Autoregressive models were developed for arterials covering 173 Traffic Analysis Zones in the suburban area in Shanghai. The results identified that the road network pattern with collector roads parallel to the arterials was shown to be associated with fewer crashes than those without parallel collectors. Higher signal density and access density also tended to increase crash frequencies on arterials.
Access management, defined in the Transportation Research Board Access Management Manual as "the ... more Access management, defined in the Transportation Research Board Access Management Manual as "the systematic control of the location, spacing, design, and operation of driveways, median openings, interchanges, and street connections to a roadway," has been shown to have a positive impact on roadway safety. Numerous studies have been conducted on the safety relationship of access management techniques as a function of access spacing, corner clearance, and medians. Several of these studies have been conducted in the United States, including studies completed in the state of Utah. The results of research performed at Brigham Young University for the Utah Department of Transportation are highlighted in this paper. Specific research includes raised median safety impacts from both a traditional analysis methodology and using Bayesian methods, as well as an analysis of access management techniques (e.g., corner clearance, access spacing, median openings, left-turn lanes, etc.) at major-arterial intersections. The purpose of the paper is to present an overview on the safety impacts of access management identified, while providing the necessary references to allow the reader to review details and specific analysis results of these and other safety studies. The results of the analyses indicate that access management techniques play a role in improving and maintaining safety along urban and suburban arterials and at major-arterial intersections in the state of Utah. Access management has, and will continue to, improve safety when implemented appropriately. Agencies across the world should identify how access management can best be implemented in their jurisdictions and apply these principles.
This report documents the first-year effort of a research project that provides recommendations f... more This report documents the first-year effort of a research project that provides recommendations for the use of access management techniques on state roadways in Texas. In the first year of the project, the research team focused on developing a matrix of guidelines for the application of different access management techniques for various roadway access classifications. The access management treatments for which recommended guidelines are presented include minimum access spacing, minimum corner clearance, median treatments, auxiliary lanes, alternate left-turn treatments, access separation at interchanges, frontage roads, and the use of traffic impact analyses for site development. The matrix allows the user to identify critical threshold criteria for the application of each access management technique, given the projected roadway access classification. The guidelines presented in this report will be valuable for state transportation professionals for use on new and retrofit projects as a toolbox of techniques for managing access to all state roadways-thus preserving the intended use of these facilities.
BRIGHAM YOUNG UNIVERSITY As chair of the candidate's graduate committee, I have read the thesis o... more BRIGHAM YOUNG UNIVERSITY As chair of the candidate's graduate committee, I have read the thesis of Jeff S. Lewis in its final form and have found that (1) its format, citations, and bibliographical style are consistent and acceptable and fulfill university and department style requirements; (2) its illustrative materials including figures, tables, and charts are in place; and (3) the final manuscript is satisfactory to the graduate committee and is ready for submission to the university library. Date Grant G. Schultz Chair, Graduate Committee
A driver approaching a signalized intersection where the light has turned yellow must make a deci... more A driver approaching a signalized intersection where the light has turned yellow must make a decision whether to stop or proceed. A signal that is properly designed will provide an opportunity for a safe and legal maneuver. As approach speeds increase, however, it becomes more difficult to execute a safe maneuver. One countermeasure that is used to help provide advance warning to drivers of an approaching intersection or the impending signal change at an approaching intersection is an advance warning signal (AWS) system. A number of AWS systems have been installed throughout the country. Four such systems were installed in the state of Utah in 2005. Since that time the effectiveness of these systems has been evaluated as a function of intersection safety. The metrics used for evaluation include crash data analysis, speed distribution analysis, and red-light running (RLR) analysis. The objective of this study is to evaluate and report the long-term effectiveness of the AWS systems installed in the state of Utah in June 2005, particularly at the intersection of Bangerter Highway and 13400 South. The results of the study indicate that overall the AWS system has generally had a positive impact on the community, with positive results noted in all areas of analysis. Given the nature of the study, however, it is difficult to quantify the extent of the overall impact as a function of only the AWS system.
Crash data are key components in transportation safety studies. In recent research completed by B... more Crash data are key components in transportation safety studies. In recent research completed by Brigham Young University (BYU) for the Utah Department of Transportation (UDOT), crash data were evaluated for 175 segments of 49 different state routes for a total of 207 miles of arterial roadway. Included in the crash dataset were the results of over 28,800 crashes aggregated by severity and collision type utilizing the UDOT web-based crash data almanac. The crash data almanac allows users to search reported crash data and establish filters for quick evaluation of results. In the research completed by BYU, crash data were evaluated to determine which characteristics of roadway sections were related to safety including crash rate, crash severity, and collision type. To accomplish this objective, several methodologies were developed to calculate crash severity scores, while the data almanac was utilized to collect crash rates and collision type data. The objective of this paper is to summarize the crash data collection process for this and other studies and to outline ways in which crash data can be useful in evaluating transportation safety. The specific application in this research is that of access management and the relationship between roadway characteristics and access management techniques. The results of this paper are expected to provide direction and guidance to engineers and planners on the use of crash data, specifically searchable crash databases, while also identifying the safety benefits of access management techniques based on the relationships between such techniques and crash histories.
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