17-11 Evaluation of Transit Priority Treatments in Tennessee

Many big cities are progressively implementing transit friendly corridors especially in urban areas where traffic may be increasing at an alarming rate. Over the years, Transit Signal Priority (TSP) has proven to be very effective in creating transit friendly corridors with its ability to improve transit vehicle travel time, serviceability and reliability. TSP as part of Transit Oriented Development (TOD) is associated with great benefits to community liveability including less environmental impacts, reduced traffic congestions, fewer vehicular accidents and shorter travel times among others.This research have therefore analysed the impact of TSP on bus travel times, late bus recovery at bus stop level, delay (on mainline and side street) and Level of Service (LOS) at intersection level on selected corridors and intersections in Nashville Tennessee; to solve the problem of transit vehicle delay as a result of high traffic congestion in Nashville metropolitan areas. This study also developed a flow-delay model to predict delay per vehicle for a lane group under interrupted flow conditions and compared some measure of effectiveness (MOE) before and after TSP. Unconditional green extension and red truncation active priority strategies were developed via Vehicle Actuated Programming (VAP) language which was tied to VISSIM signal controller to execute priority for transit vehicles approaching the traffic signal at 75m away from the stop line. The findings from this study indicated that TSP will recover bus lateness at bus stops 25.21% to 43.1% on the average, improve bus travel time by 5.1% to 10%, increase side street delay by 15.9%, and favour other vehicles using the priority approach by 5.8% and 11.6% in travel time and delay reduction respectively. Findings also indicated that TSP may not affect LOS under low to medium traffic condition but LOS may increase under high traffic condition

Simulating the Impact of Traffic Calming Strategies

This study assessed the impact of traffic calming measures to the speed, travel times and capacity of residential roadways. The study focused on two types of speed tables, speed humps and a raised crosswalk. A moving test vehicle equipped with GPS receivers that allowed calculation of speeds and determination of speed profiles at 1s intervals were used. Multi-regime model was used to provide the best fit using steady state equations; hence the corresponding speed-flow relationships were established for different calming scenarios. It was found that capacities of residential roadway segments due to presence of calming features ranged from 640 to 730 vph. However, the capacity varied with the spacing of the calming features in which spacing speed tables at 1050 ft apart caused a 23% reduction in capacity while 350-ft spacing reduced capacity by 32%. Analysis showed a linear decrease of capacity of approximately 20 vphpl, 37 vphpl and 34 vphpl when 17 ft wide speed tables were spaced at 350 ft, 700 ft, and 1050 ft apart respectively. For speed hump calming features, spacing humps at 350 ft reduced capacity by about 33% while a 700 ft spacing reduced capacity by 30%. The study concludes that speed tables are slightly better than speed humps in terms of preserving the roadway capacity. Also, traffic calming measures significantly reduce the speeds of vehicles, and it is best to keep spacing of 630 ft or less to achieve desirable crossing speeds of less or equal to 15 mph especially in a street with schools nearby. A microscopic simulation model was developed to replicate the driving behavior of traffic on urban road diets roads to analyze the influence of bus stops on traffic flow and safety. The impacts of safety were assessed using surrogate measures of safety (SSAM). The study found that presence of a bus stops for 10, 20 and 30 s dwell times have almost 9.5%, 12%, and 20% effect on traffic speed reductions when 300 veh/hr flow is considered. A comparison of reduction in speed of traffic on an 11 ft wide road lane of a road diet due to curbside stops and bus bays for a mean of 30s with a standard deviation of 5s dwell time case was conducted. Results showed that a bus stop bay with the stated bus dwell time causes an approximate 8% speed reduction to traffic at a flow level of about 1400 vph. Analysis of the trajectories from bust stop locations showed that at 0, 25, 50, 75, 100, 125, 150, and 175 feet from the intersection the number of conflicts is affected by the presence and location of a curbside stop on a segment with a road diet

Sensitivity Analysis on Traffic Crash Prediction Models by Using STATA

Traffic accidents results from the interaction of different parameters which includes highway geometrics, traffic characteristics and human factors. Geometric variables include number of lanes, lane width, median width, shoulder width, roadway length, number of intersections, access density and shoulder width while traffic characteristics include AADT and speed. The effect of these parameters can be correlated by predictive models that predict crash rates at particular roadway section. STATA software commands it can be used to test the sensitivity of these variables on crash rate after modeling. In the current research sponsored by Florida Department of Transportation titled "Evaluation of Geometric and Operational Characteristics affecting the safety of Six-lane divided Roadways" we use these commands to determine the effect in crash rate as the result of change on these independent variables. We selected our model based on the user written command nbvargr which gives dispersion factor between Poisson and Negative Binomial. By using Vuong's value we were able to choose between Zero-Inflated and normal models. Through the command listcoef, percent we determine percent change in crash rate for unit and standard deviation increase in independent variables. By using the command mfx compute we were able to determine numerically the marginal effects or the elasticities between crash rate and the independent variables. These commands and others built in STATA reveal if the increase in size or dimension for roadway geometrics will result in higher crash rate or reduction.

15-09 Impact of Access Management Practices to Pedestrian Safety

This study focused on the impact of access management practices to the safety of pedestrians. Some of the access management practices considered to impact pedestrian safety included limiting direct access to and from major streets, locating signals, limiting the number of conflict points and separating conflict areas, removing turning vehicles from through traffic lanes, using nontraversable medians to manage left-turn movements and providing a supporting street and circulation system. The study evaluated through statistical modeling the correlation between access management practices to pedestrian crashes. Focused on the impacts of access management on pedestrian crashes, eight (8) major roadway corridors were selected and utilized for analysis. Utilizing Negative Binomial, the correlation between roadway features and pedestrian crashes were modeled. Four variables including AADT, access density, percentage of trucks and the presence of TWLT were found to be positively associated with the pedestrian crash frequency. Variables such as the presence of median, presence of crosswalk, presence of shoulders, presence of sidewalk and high speed limit had negative coefficients hence their increase or presence tends to decrease pedestrian crashes. It could therefore be concluded that though these variables had some influence on the pedestrian crashes, access density, crosswalk, sidewalk and speed limit were the most statistically significant variables that determined the frequency of the pedestrian crashes

14-07 Development of Decision Support Tools to Assess Pedestrian and Bicycle Safety: Focus on Population, Demographic and Socioeconomic Spectra

Despite the increase of these non-motorized trips, bicyclists and pedestrians remain vulnerable road users that are often over represented in traffic crashes. While the currently used methods that identify hazardous locations serve their purpose well, majority represent a reactive approach that seeks improvement after crashes happen. This research addressed these issues and proposed decision support tools to aid the implementation of bicycle and pedestrian safety strategies. This work developed an access based tool to predict the expected number of crashes at different neighborhood levels. This tool combines the traditional methods such as those provided in the Highway Safety manual to predict the expected number of bicycle and pedestrian crashes. First, a cluster analysis technique is proposed and developed a Geographic Information Systems (GIS) technique to facilitate the identification of high crash locations. Safety Performance Functions (SPFs) are developed in form of mathematical equations to relate the number of crashes to area socioeconomic and demographic characteristics. An integrated system consisting of access database and safety performance functions, and whose interface is designed to automatically compute the number of crashes given the input values is developed. Basing on crash value, the tool can be adopted as a framework to guide the appropriate allocation of safety improvement resources

16-11 Microsimulation of the Impact of Access Management Practices to Pedestrians

The study applied microsimulation to analyze the impact of access management (AM) to the operational performances of vehicles and pedestrians. A conceptual model was developed in VISSIM and VISWALK to examine the effect of access and signals density on different median types to the travel speed, travel time, delay and stopping. Access density, signal density, and presence of median were simulated in a scenario base analysis. The model scenarios shifted through changing both access density and signal density with no median, raised median and TWLT lane to provide interactions of arterial corridors in Nashville. The effect of access density on speed, delay and travel time was very vivid for the vehicles within the corridors showing speed decreasing with the increase in access density while delay increased and the number of stops increased. Additionally, as signal density increased, a decreasing pattern in corridor vehicle speed was observed. Pedestrian performances changes were less dramatic indicating that access density had a minimal effect on the pedestrian speed operations. The same trend was observed on signal density which affected pedestrian speed by a small decrease as signal density increased. The findings may provide useful understanding to state policy makers in implementing Access Management guidelines

Exploring Factors Contributing to Injury Severity at Freeway Merging and Diverging Locations in Ohio

Identifying factors that affect crash injury severity and understanding how these factors affect injury severity is critical in planning and implementing highway safety improvement programs. Factors such as driver-related, traffic-related, environment-related and geometric design-related were considered when developing statistical models to predict the effects of these factors on the severity of injuries sustained from motor vehicle crashes at merging and diverging locations. Police-reported crash data at selected freeway merging and diverging areas in the state of Ohio were used for the development of the models. A generalized ordinal logit model also known as partial proportional odds model was applied to identify significant factors increasing the likelihood of one of the five KABCO scale of injury severity: no injuries, possible/invisible injuries, non-incapacitating injuries, incapacitating injuries, or fatal injuries. The results of this study show that semi-truck related crashes, higher number of lanes on freeways, higher number of lanes on ramps, speeding related crashes, and alcohol related crashes tend to increase the likelihood of sustaining severe injuries at freeway merging locations. In addition, females and older persons are more likely to sustain severe injuries especially at freeway merge locations. Alcohol related crashes, speeding related crashes, angle-type collisions, and lane-ramp configuration type D significantly increase the likelihood of severe injury crashes at diverging areas. Poor lighting condition tends to increase non-incapacitating injuries at diverging areas only. Moreover, adverse weather condition increases the likelihood of no-injury and fatal injuries at merging areas only and adverse road conditions tend to increase a range of injury severity levels from possible/invisible injuries to incapacitating injuries at merging areas only. Highlights Semi-truck, lanes on freeways and ramps, speeding, angle collisions, and alcohol increase severe injuries at merging areas. Females and older persons sustain severe injuries at freeway merge locations. Alcohol, speeding, angle collisions, and lane-ramp type D increase severe injuries at diverging areas. Adverse weather condition increases no-injury and fatal injuries at merging areas only. Adverse road condition tends to increase a range of non-fatal injury levels at merging areas only

Comprehensive Analysis on the Conversion of the Existing HOV Lanes into Hot Lanes in Tennessee

This study analyzed the conversion of HOV Lanes to HOT Lanes in Tennessee. The research applied several approaches including microsimulations of HOV/HOT Lanes that employed data from Greater Nashville Regional Council (GNRC) travel demand model and field collected traffic counts. Microsimulation was conducted through VISUM and VISSIM software by importing TransCAD based GNRC traffic travel demand. Apart from the comprehensive literature review on HOT Lane effectiveness from other states, the study reviewed best practices from other cities and states on conversion of HOV Lanes to HOT Lanes, enforcement, violation and penalty structures, and policy initiatives. A total of four scenarios were evaluated including:(1) the base scenario with HOV Lanes without effective enforcement as it is currently operated (2) HOV Lanes converted to HOT Lanes with no intermediate access (3) HOT Lanes with one intermediate access point and (4) HOT Lanes with multiple access points along the current HOV Lane corridors. The study found that converting HOV Lanes to HOT Lanes without intermediate access performs better (meaning reduced travel time) when compared to HOT Lanes with additional intermediate entrance/exit points. With HOT Lanes, travel time for all traffic along major interstate highways in Tennessee will be reduced by an average of 23% from the current travel times. Travel time for the traffic that will be using the HOT Lanes along major interstate highways in Tennessee will be much reduced compared to other GP lanes from the current travel times. Key findings from the case studies of other regions and Cities with currently operating HOT Lanes view them as effective means to manage congestion. Given the proper commitment by TDOT, HOT Lanes have the potential to be a better and more efficient usage of resources to relieve congestion on highways than the construction of more general-purpose lanes. Study recommends TDOT convert the current HOV Lanes to HOT Lanes without intermediate access (entrance/exit). The entrance/exit points should be only at the beginning and end of the HOT Lanes. Study recommends a toll fee of 10 cents per mile and tolls should be collected electronically (static or dynamic tolls). Study recommends that separation of the HOT Lanes and GP lanes should be through pavement marking (not physical barriers). Only single occupant vehicles (SOV) will be required to pay tolls, and all HOVs (2+) using the HOT Lane will be exempted from toll payment. Dynamic Message Signs should be initially located 1 mile prior to the starting of the HOT Lane to provide travel alerts and incident information. Video cameras installed along HOT corridors must be used for violators\u2019 identification and incident detection

EVALUATION OF GEOMETRIC AND TRAFFIC CHARACTERISTICS AFFECTING THE SAFETY OF SIX-LANE DIVIDED ROADWAYS By

I would like to express my gratitude to all those who gave me the possibility to complete this thesis. I want to thank the Florida Department of Transport safety office for giving me permission to use their database to extract data for this research. Special thanks should go to Pat Brady, Benjamin Jacobs and Charles Anderson who were readily available to give me access to their database. I am deeply indebted to my supervisor Prof. Dr. Renatus Mussa whose help, stimulating suggestions and encouragement helped me in all the time of research for and writing of this thesis. My sincere thanks also go to Dr. John Sobanjo and Lisa Spainhour who were my committee members in this research. They were available all the time to give me some directives and corrected me where was required. I would like also to thank my fellow research members at traffic laboratory who were with me all the time, giving me new ideas, and correcting me several times. I would like to thank Mr. Victor Muchuruza for his tremendous job in giving me new ideas in modeling and analysis. I would like also to thank Mr. Thobias Sando for his spiritual advices and Valerian Kwigizile who was my office mate. My final thanks go to Sprinkle Consulting who were the consultants for this project