Browsing by Author "Medina, Alejandra"

Now showing 1 - 11 of 11
  • Thumbnail Image
    Analyzing Intersection Gap Acceptance Behavior with Naturalistic Driving Data
    Li, Yingfeng (Eric); Hao, Haiyan; Gibbons, Ronald B.; Medina, Alejandra (National Surface Transportation Safety Center for Excellence, 2022-09-14)
    Safety at unsignalized intersections continues to be a major concern for transportation agencies and roadway users. To improve intersection safety, this project conducted a comprehensive study of gap acceptance behaviors at unsignalized intersections using the second Strategic Highway Research Program (SHRP 2) naturalistic driving study (NDS) data. The team collected 1,170 accepted and rejected gaps/lags based on 466 NDS trips at 60 unsignalized T-intersections in Washington state and North Carolina. The project team utilized a number of data sources, including time series data measuring vehicle kinematics for the analyzed trips, forward-facing and rear-view videos for the analyzed trips, driver demographic and driving history data, the SHRP 2 Roadway Information Database, and satellite images. First, the team identified the critical gaps for a number of common scenarios using three widely accepted methods: binary logistic regression, maximum likelihood method, and probability equilibrium method. Results showed an overall critical gap of 5.3 seconds for right-turning trips and 6.2 seconds for left-turning trips. The team then went on to develop a complete understanding of the factors affecting gap acceptance decisions using logistic regression and machine learning techniques. A number of factors were identified that affect drivers’ gap acceptance decisions, including being a gap instead of a lag, presence of leading and/or following vehicles, higher volume, intersection being unskewed, and increased number of through lanes. Finally, researchers further investigated drivers’ longitudinal and lateral acceleration behaviors during turning after accepting a gap and factors affecting their turning behaviors. Overall, both left- and right-turning vehicles initially accelerated quickly after they accepted a gap, and then reduced to a lower but prolonged acceleration rate while turning to reach a desired speed. For lateral acceleration, the peak value for the left-turning profile was reached later in the turning process than for the right-turning profile.
  • Thumbnail Image
    Application of Naturalistic Truck Driving Data to Analyze and Improve Car Following Models
    Higgs, Bryan James (Virginia Tech, 2011-12-02)
    This research effort aims to compare car-following models when the models are calibrated to individual drivers with the naturalistic data. The models used are the GHR, Gipps, Intelligent Driver, Velocity Difference, Wiedemann, and the Fritzsche model. This research effort also analyzes the Wiedemann car-following model using car-following periods that occur at different speeds. The Wiedemann car-following model uses thresholds to define the different regimes in car following. Some of these thresholds use a speed parameter, but others rely solely upon the difference in speed between the subject vehicle and the lead vehicle. This research effort also reconstructs the Wiedemann car-following model for truck driver behavior using the Naturalistic Truck Driving Study's (NTDS) conducted by Virginia Tech Transportation Institute. This Naturalistic data was collected by equipping 9 trucks with various sensors and a data acquisition system. This research effort also combines the Wiedemann car-following model with the GHR car-following model for trucks using The Naturalistic Truck Driving Study's (NTDS) data.
  • Thumbnail Image
    Assessing the Safety Impact of Roadway Improvements Using Naturalistic Driving Data--Feasibility Study
    Li, Yingfeng; Medina, Alejandra; Gibbons, Ronald B. (National Surface Transportation Safety Center for Excellence, 2017-10-19)
    This project explored the feasibility of using Second Strategic Highway Research Program (SHRP 2) data, including the Roadway Information Database (RID), to evaluate the effectiveness of roadway safety improvements where traditional crash data are limited. The research team conducted two case studies based on naturalistic driving study (NDS) data from 200 trips. The two case studies evaluated the safety effects of (1) a paving project with newly installed pavement and markings, and (2) a median barrier replacement project with a newly installed and restored concrete median. A number of safety surrogate measures were used to develop a comprehensive understanding of how driver behavior changed with and without the safety treatment. The results from both case studies indicated that the roadway improvements had an impact on driver safety behavior, as indicated through the surrogate safety measures of speed, lateral and longitudinal accelerations, lane deviation, and car-following behavior. The two case studies illustrate two different methods for studying the effectiveness of roadway improvements on safety. The paving project case study compared driver behavior data collected at the project site after the roadway improvement with data from an adjacent site with similar roadway conditions but without the pavement improvement. The median barrier project case study compared data on the same segment of road before and after the improvement project. The two different methods illustrate the flexibility available with SHRP 2 safety data. In addition to the case studies, the research team also assessed the availability, suitability, and limitations of SHRP 2 and RID data for evaluating the safety impact of roadway improvements.
  • Thumbnail Image
    Effectiveness of Lighted Work Zone Apparel: Effects on Visibility
    Bhagavathula, Rajaram; Kassing, Andrew; Gibbons, Ronald B.; Medina, Alejandra (National Surface Transportation Safety Center for Excellence, 2022-11-11)
    In United States, collisions between vehicles and workers in a work zone are a major problem. In 2020, there were 157 worker fatalities in work zone in the United States. Increasing worker conspicuity has the potential to reduce to fatalities by making them more visible to motorists. Retroreflective vests (Class 3) and trousers (Class E) worn by workers in a nighttime work zone are passive in nature; i.e., they require light from oncoming vehicle headlamps to work. The advancement of LED technology has made it easy to install them on retroreflective vests and hard hats to increase their conspicuity. Multiple configurations of LEDs and flash patterns installed on vests and hard hats could be used to increase worker conspicuity. Further, equipment manufacturers are now offering work zone apparel and head protection which incorporate lights into portions of the retroreflective material, or adds light to a specific piece of equipment (hard hats). One of the major benefits is that these do not require external light sources for activation whereas retroreflective material relies on an eternal light source. According to manufacturers, the new apparel and equipment improve visibility, and the pieces are washable. There is also the potential for lighted apparel that uses colors or operating features (such as flash patterns) to further increase worker conspicuity. However, a typical work zone is a visually cluttered with flashing lights on work vehicles. Therefore, it is important that the selected configuration of lights on workers apparel are not masked by the visual clutter in the work zone. The conspicuity of passive (retroreflective material only) and active (both retroreflective and LEDs) apparel in a work zone will help in determining the apparel that would increase the conspicuity of the workers in the work zone. The goal of the current study is to evaluate effectiveness of lighted work zone apparel under realistic conditions. More specifically, the goal is to compare the effectiveness of various kinds of lighted worker apparel (colors, flash patterns, lighted hard hat, etc.) to that of standard retroreflective material under varying visually cluttered conditions. In the current study, the effects of worker apparel and scene clutter on driver visual performance were evaluated under realistic work zone conditions. Driver visual performance was measured indirectly using the detection distance of work-zone workers as indicated by participants as they drove through the simulated work-zone environment. The results of the current study show that lighted worker vests and helmet-mounted lights plays a critical role in increasing the conspicuity of workers in active nighttime work-zone environments with visually cluttered environments. Lighted work-zone vests with white-colored LEDs paired with helmet-mounted LEDs (also white colored), either in flashing or in a steady-on condition, had the longest detection distances. Standard Class 3 retroreflective vests had the lowest detection distances among all the garments evaluated. When workers wore the lighted apparel with red and white LEDs without the lighted helmet, the detection distances were shorter than with the lighted helmet but longer than with the retroreflective vest alone. Based on these results, a combination of lighted garments along with a lighted helmet, preferably in a flashing pattern or steady-on, are recommended to increase the conspicuity of workers in active nighttime work-zone environments.
  • Thumbnail Image
    Enhanced Rear Signaling (ERS) for Heavy Trucks: Phase III – Development of Field Operational Test
    Schaudt, William A.; Bowman, Darrell Scott; Trimble, Tammy E.; Medina, Alejandra; Bocanegra, Joseph L.; Baker, Stephanie Ann; Marinik, Andrew; Wierwille, Walter W.; Hanowski, Richard J. (Virginia Tech Transportation Institute, 2010-09)
    The Enhanced Rear Signaling (ERS) for Heavy Trucks project was directed at investigating methods to reduce or mitigate those crashes where a heavy truck has been struck in the rear by another vehicle. Prior to the current effort, two phases of work had been completed on this project. The purpose of the current effort, Phase III, focused on exploring the benefits of the countermeasures developed in previous phases, and to develop a plan for a large scale Field Operational Test (FOT). During crash database analyses in the current project it was found that, in 2006, there were approximately 23,500 rear-end crashes involving heavy trucks which resulted in 135 fatalities and 1603 incapacitating injuries. Many different types of ERSs were investigated in this study across both the auditory and visual modalities. Visual warning signals were found to be the most beneficial at signaling following-vehicle drivers (more specifically rear warning-light configurations). The research team recommended that one specific configuration be selected for real-world data collection based on its high performance and the potential success of future design implementation. Overall, the final radar-based cautionary ERS system was robust in real-world driving conditions and is recommended for an FOT.
  • Thumbnail Image
    Equity in Transportation Safety
    Robinson, Sarah; Medina, Alejandra; Gibbons, Ron; Kassing, Andrew; Myers, Bradley (National Surface Transportation Safety Center for Excellence, 2024-09-24)
    Equity in transportation is a key issue for the Federal Highway Administration (FHWA), as well as state departments of transportation. Equitable transportation ensures safety for all road users across all modes of transportation for all communities. FHWA recommends the adoption and equitable application of a safe system approach to achieve Vision Zero objectives to eliminate traffic fatalities and severe injuries. A safe system fundamentally recognizes human error and accounts for it when designing systems and operations. Incorporating equity into roadway safety data is critical for conducting data-driven safety analysis. FHWA recommends collaboration with underserved communities through a process of collecting and analyzing data, engaging community representatives, implementing improvements, and evaluating impacts. Ensuring robust and accurate data is critical. State programs have worked to incorporate a wide variety of data into their crash models. Social and demographic data such as race, ethnicity, gender, age, education, employment status, income level, disability status, among many other variables, have been evaluated and demonstrated to be factors in the frequency of crashes. States have published mapping tools to visualize data trends and identify locations for targeted implementation efforts in conjunction with scoring metrics for evaluating proposed solutions.
  • Thumbnail Image
    Examination of the Current Practice of Lighting in Virginia: Nighttime Work Zones and Improving Safety Through the Development of Nighttime Lighting Specifications
    Bhagavathula, Rajaram; Gibbons, Ronald B.; Medina, Alejandra; Terry, Travis N. (Virginia Transportation Research Council, 2017-09)
    This project evaluated current nighttime work zone lighting practices for limited-access highways and primary routes in Virginia through (1) an on-site evaluation of lighting levels in work zones; (2) an illuminance characterization of various commercially available light towers; and (3) a human factors evaluation of those light towers and developed effective nighttime work zone lighting requirements for Virginia. The majority of the static nighttime work zones used metal halide portable light towers. Mobile operations such as milling and paving used equipment-mounted balloon lights and LEDs. Horizontal illuminance levels in the work zones were affected by the number of light towers, locations of the light towers, and number of traffic lanes in the work zone. The measured horizontal illuminance levels in the work zones were much higher than recommended levels. Milling and paving operations that used equipment-mounted lights had lower illuminance levels than operations that used portable light towers. Vertical illuminance levels in the traffic lane were significantly affected by the aiming of the luminaires on the portable light towers. Luminaires aimed into the traffic travel lane produced higher vertical illuminance levels, which can result in disability and discomfort glare and consequently reduce visibility. The visual performance of drivers in a work zone can be influenced by the type and orientation of the light tower. An orientation aimed toward the driver resulted in lowering drivers’ visual performance, both objectively and subjectively. This decrease in visual performance could be attributed to higher vertical illuminance. To increase the drivers’ visual performance and reduce glare in the work zone, efforts should be taken to aim the light towers in an active nighttime work zone away from the direction of traffic or perpendicular to it. In these orientations, all the three light towers tested had similar visual performance measures. The increase in the mean vertical illuminance level in the critical range is associated with higher perceived ratings of glare. Results showed that the mean vertical illuminance in the distance range of 260 to 65 ft to the light tower could be used as an objective measure of glare. A mean vertical illuminance of less than 17 lux resulted in lower perceived glare ratings. Results also indicated that light towers should be oriented so that the angle between the beam axis and driver line-of-sight axis is always greater than or equal to 90 degrees. Finally, a draft specification outline including a plan for on-site lighting evaluation of a work zone is presented.
  • Thumbnail Image
    Safety Countermeasures at Unsignalized Intersections – A Toolbox Approach
    Li, Eric; Medina, Alejandra; Gibbons, Ronald B. (National Surface Transportation Safety Center for Excellence, 2020-06-23)
    In 2015, approximately 8,000 intersection and intersection-related fatal crashes occurred on the nation’s highway system, resulting in more than 8,400 fatalities. That death toll represented about 24% of the traffic-related deaths across the country. Combining fatalities and injuries, intersection and intersection-related crashes represent more than 50% of the traffic-related injuries across the nation. Unsignalized intersections are of particular concern. Between 2010 and 2014, unsignalized intersections were responsible for more than 70% of the intersection and intersection-related fatalities. This report documents 83 suitable safety countermeasures that can be used at unsignalized intersections to mitigate crash risks. A number of these have potential for cost-effective, systemic implementation, including LED-enhanced Stop signs, retroreflective panels on sign posts, center line pavement markings in a median crossing, center line pavement markings on the minor road approach, and installation of intersection lighting.
  • Thumbnail Image
    Speed Management Countermeasures: Gaps and Opportunities
    Wotring, Brian; Medina, Alejandra; Antin, Jonathan F. (National Surface Transportation Safety Center for Excellence, 2023-02-01)
    The number of speeding-related crashes continues to be a major concern on U.S. highways, with 29% of roadway fatalities determined to be due to speeding (National Center for Statistics and Analysis, 2022). To reduce the number of fatalities and move towards a goal of zero roadway deaths, it is important to understand the risks and factors that lead to speeding behaviors as well as to evaluate currently deployed speeding countermeasures. In order to determine the state of speeding countermeasures, a highly targeted literature review was focused on published documentation from national agencies and the peer-reviewed literature. These specific sources were chosen to rely solely on the highest quality countermeasure information currently available. Using these sources, a gap analysis was then completed based on statements and postulations within the noted literature. Additionally, the research team engaged in a brainstorming session to determine additional gaps and potential opportunities for improved countermeasure implementation not yet represented in the formal literature. Finally, the research team also collected information on several speeding campaigns and initiatives currently in place. In order to better organize the findings, they were grouped by domain. Such groups include advanced technologies, education and outreach, enforcement, engineering, and other. Overall, the review of documentation on speeding countermeasures revealed a large number of gaps and opportunities in the current knowledge space. One benefit of housing so many in a single location is to aid in the process of hypothesis generation. This collection may prove useful in guiding or eliciting future ideas.
  • Thumbnail Image
    Traffic Sign Characteristics for Machine Vision Safety Benefits
    Kassing, Andrew; Gibbons, Ronald B.; Li, Eric; Palmer, Matthew; Hamen, Johann; Medina, Alejandra (National Surface Transportation Safety Center for Excellence, 2024-07-03)
    Machine vision has become a central technology for the development of automated driving systems and advanced driver assistance systems. To support safe navigation, machine vision must be able to read and interpret roadway signs, which provide regulatory, warning, and guidance information for all road users. Complicating this task, transportation agencies use a large variety of signs, which can have significantly different shapes, sizes, contents, installation methods, and retroreflectivity levels. Additionally, many environmental factors, such as precipitation, fog, dew, and lighting, also affect the visibility and legibility of roadway signs. Understanding how environmental factors and sign conditions affect machine vision performance will be important for transportation agencies to maximize the technology’s safety benefits. Research began by conducting a literature review cataloguing current research concerning roadway sign and visual performance, vehicle vision systems, and sign significance for automated driving. Information and insight gained during the literature review process informed the design and system development of data collection systems. Field data collection was then performed over the course of 3 months in late spring to early summer in 2021. Simultaneously, sign data were harvested using Google Street View and mapped using ArcGIS. Data collected during the experimental trips were then reduced and carefully prepared for analysis. Researchers conducted a thorough data analysis, particularly looking at sign location, viewing distance, sign color, font size, sun position, and illumination, to assess the impact of many environmental and infrastructure factors on the legibility of sign characters. Results showed that blue and brown signage with white legend text provided the best chance of sign character legibility during the daytime; sign characters were easy to read during the day at all three experimental distances (200, 400, and 500 ft), with small characters becoming less legible as view distance increased; daytime legibility decreased as light levels decreased; sign images captured at nighttime illumination levels had poor legibility results; sign characters on overhead signage were found to be more legible and are expected to be identified at a higher rate by vehicle vision systems; and vehicle vision systems should use a high-quality camera capable of taking pictures at night without motion blur.
  • Thumbnail Image
    Understanding Crashes Involving Roadway Objects with SHRP 2 Naturalistic Driving Study Data
    Li, Eric; Hao, Haiyang; Gibbons, Ronald B.; Medina, Alejandra (National Surface Transportation Safety Center for Excellence, 2023-03-08)
    This project used the second Strategic Highway Research Program (SHRP 2) naturalistic driving study (NDS) data as an alternate data source to police-reported crash data to better understand roadway object crashes. The objectives included determining crash causation, recommending strategies for crash prevention, and understanding the implications for highly automated vehicles (HAVs). Researchers addressed these objectives with a three-pronged approach: (1) a detailed engineering study of roadway object events to identify and quantify effects of a large number of relevant variables; (2) a machine-vision-oriented study to document the implications of roadway object events on machine vision performance; and (3) a detailed case study analysis of representative roadway object events to provide further qualitative results on how and why roadway object crashes occur and what potential actions can prevent such events effectively.