These poster presentations on roadway design vary from research conducted on autonomous vehicles and the impacts on roadway design, interchange design, intersection design, overall roadway design, and rural roadway design.
Eliminating Infrastructure Barriers for Autonomous Driving: A Voxel-based Raycasting Approach to Assess Highway Design
Maged Gouda (email@example.com), University of AlbertaShow Abstract
Ishaat Chowdhury, University of Alberta
Jonas Weiß, Technical University of Munich
Alexander Epp, University of Alberta
Karim El-Basyouny, University of Alberta
Several highway design elements are presently determined based on constraints due to human drivers. Autonomous vehicles (AV) are expected to replace human drivers with an expectation of having differing driving characteristics. It is, therefore, imperative that current infrastructure is reassessed for autonomous driving scenarios. This paper proposes a novel approach for the assessment of sight distance and speed limits for autonomous vehicles along road infrastructure using LiDAR data. The proposed method considers observer points, representing the vehicle sensors, and target points, representing the vehicle’s path, along the road, then uses viewability and occlusion due to the road and roadside obstructions to determine available sight distance. Based on available sight distance as well as the AV and road characteristics, safe driving speed limits are also calculated. An alternative algorithm was used in order to compare it with the proposed approach and was found to produce results agreeing within 1.5%. As evident from the analysis, certain AV scenarios may lead to unsafe driving conditions for autonomous vehicles. Such information are crucial as it allows policy-makers to design guidelines and legislation to prevent unsafe driverless vehicle scenarios.
Eliminating Infrastructure Barriers for Autonomous Driving: A Case of Vertical Curve Design
Maged Gouda (firstname.lastname@example.org), University of AlbertaShow Abstract
Bruno Mello, University of Sao Paulo
Joshua Visser, Associated Engineering
Karim El-Basyouny, University of Alberta
The gradual introduction of autonomous vehicles (AVs) is expected to cause a significant improvement in road safety. While most of the advances will come about due to the introduction of automation, existing road infrastructure must be examined for its compatibility with AV systems and sensors, as current designs focus entirely on compatibility with human drivers. Accordingly, representatives from the automotive industry, governments, and academia have supported research on ways to prepare existing road networks for AVs. One aspect of roadways affecting AV compatibility is road grade and curvature. Highway vertical curves might pose restrictions to available sight distance (ASD). As Autonomous vehicles rely on sensory systems, reassessment of existing roadways is required to validate the safe operation of AVs. This paper, therefore, proposes a novel approach for the extraction of roadway vertical alignment data from 3D point clouds. The extracted road vertical profile is used to estimate the vertical curve sight distance and maximum safe speed based on AV design parameters. Out of 33 curves, six curves were found to exhibit limitations in their SD, resulting in maximum travel speeds that are lower than the design speed of the tested highways. For the remaining curves, it was found that the maximum speed could be increased above the current speed limits if all the vehicles using the facility are autonomous. On average, the analysis revealed that the required reduction in travel speeds was 11% (12.04 km/h), and the safe allowable increase in speeds was estimated at 23.63% (26 km/h).
Designing Highway Alignments for Fully-automated Vehicles
Xinchen Ye, Tongji UniversityShow Abstract
Xuesong Wang (email@example.com), Tongji University
Shuang Liu, Tongji University
In recent years, the development and testing of automated driving technology have been widespread around the world. However, due to differences in perception abilities between automated vehicles and human drivers, the current geometric design controls for highway alignments, designed for human drivers, may not be applicable to automated vehicles. Few studies, though, have systematically investigated the design control computation methods for highway alignments, though we face full driving automation in the near future. In this study, design controls for vertical alignments and combined horizontal and vertical alignments were separately computed for automated vehicles considering perception abilities, including perception-reaction time (PRT), perception height, angle, and distance. The stopping sight distance (SSD) and the length of sag and crest vertical curves were derived and compared with those for human drivers. Computations for combined alignments were based on coordination guidelines: minimum length of horizontal curve was analyzed when obeying the guidelines, and preview sight distance (PVSD) was computed when disobeying them. Results show: 1) design controls on vertical curves are more tolerant for automated vehicles than for human drivers; 2) perception distance of current common sensors might not be able to meet the required SSD at higher speeds or on steeper downgrades; 3) the dominating criterion of sag vertical curve design controls differ between automated vehicles and human drivers.
How Autonomous Vehicles May Influence Vertical Curves, At-Grade Railroad Crossings, And Ramp Terminals
David McDonald, Hanson Professional Services, Inc.Show Abstract
This paper builds on the author’s 2017 work on how connected vehicles/autonomous vehicles (CV/AV) may impact the geometric design of roads (1, 2). The previous work explored the potential modifications to stopping sight distance and provided some thoughts on the potential impacts to lane and shoulder widths, roadside modifications, intersections, and parking. How these differences between the human driver and the expected performance of fully automated vehicles may impact the design of roads are further explored in this paper, with attention on vertical curves, at-grade rail crossings, and ramp terminals. Three situations are considered: AV-only roads, AV-separated roads, and mixed-use roads (AV and human-driven vehicles in the same vehicle stream).
Enhancing the Operational Efficiency of Signalized Diamond Interchanges with the New Displaced Diverging Diamond Interchange
Peter Yu (firstname.lastname@example.org), University of WashingtonShow Abstract
The signalized diamond interchange is the most common type of highway interchange and comprises the vast majority of service interchanges in the United States, providing numerous essential freeway-to-arterial connections. However, the traffic congestion experienced at traditional diamond interchanges with traffic signal control has become a challenging issue, especially in urban and suburban areas where traffic volumes are high and right-of-way is scarce. Many existing diamond interchanges are incapable of handling current traffic demands, creating both safety and operational problems. This paper introduces and examines a new service interchange design, the displaced diverging diamond interchange (DDI), which can overcome the limitations of conventional diamond interchanges as well as other diamond interchange configurations. Through a comprehensive series of microscopic simulation tests, the software PTV Vissim was used to analyze the operational performance of the displaced DDI in comparison to three commonly used diamond interchange forms–the conventional diamond interchange, single-point urban interchange, and diverging diamond interchange–over a range of traffic volume conditions, and the four interchange designs were compared using two measures of effectiveness (MOEs). Altogether, the results from the simulations demonstrate that the new displaced DDI performed statistically significantly better than all other three existing interchange designs in the vast majority of scenarios. Specifically, over the range of tests, the displaced DDI consistently provided significantly lower travel times, many fewer stops, and a considerably higher capability to serve large amounts of traffic. The displaced DDI shows great promise for substantially improving traffic operations at diamond interchanges suffering from congestion.
Examination and Modeling of Driver Behavior on Entrance Freeway Ramp Terminals Using Naturalistic Driving Study Data
Mohannad Alyamani, Carleton UniversityShow Abstract
Yasser Hassan, Carleton University
This paper studies driver behavior on freeway entrance ramp terminals using trip data from the SHRP-2 Naturalistic Driving Study (NDS) database from two different US states. The study included first a qualitative assessment of the driver speed behavior as they navigate the ramp and speed change lane (SCL). A trend of continuous vehicle acceleration was evident from the beginning of the ramp controlling curve that continued after merging onto the freeway right lane (FRL). It was also found that a portion of the drivers tend to merge onto the FRL on the taper after the SCL had ended, with this behavior being dominant on the taper-type SCL. Statistical tests showed that the driver behavior measures in general follow a normal distribution at each site. Tests of hypothesis examined the differences of different driver behavior measures on the study sites, and it was shown that the speed and acceleration behavior of the drivers differs on the different sites indicating that it depends on the complete set of geometric characteristics at the site. Linear-mixed models were developed for the speed and acceleration behavior measures to account for the repeated measures caused by repeated trips by the same drivers in the dataset.
Evaluating Safety Performance of the Offset Diamond Interchange Design using VISSIM and Surrogate Safety Assessment Model
Amirarsalan Mehrara Molan, California Polytechnic State UniversityShow Abstract
Joseph Hummer, North Carolina Department of Transportation
Logan Aspeitia, California Polytechnic State University
Alex Deatherage, California Polytechnic State University
Many of existing interchanges, which were built mostly in 1950s and 1960s based on old design guidelines, have operational and/or safety problems due to the inconsistency with current traffic and pedestrian demands. Therefore, upgrading existing designs based on recent policies and demands could result in improving the performance of old interchanges. This research evaluates traffic safety and pedestrian performance of the new offset diamond interchange (ODI) as a substitute for failing conventional interchanges. The ODI design, which showed potential in improving traffic operation in a past study by the authors, were compared to nine interchange designs using VISSIM and the Surrogate Safety Assessment Model (SSAM) in this study to examine the safety and pedestrian performance. Overall, 324 simulation scenarios were tested with various conditions of traffic and pedestrian volumes, turning traffic ratios, traffic distribution, and truck percentages. According to the results, the ODI showed potential to be a promising design in terms of safety and pedestrian performance. However, the diverging diamond interchange (DDI) resulted in fewer simulated conflicts compared to the new ODI. On the other hand, the ODI design had a better performance in terms of pedestrian performance.
Collecting and Extracting Trajectories of Freeway Ramp Vehicles Using Unmanned Aerial Vehicles and Video Processing
Fayez Alamry, Carleton UniversityShow Abstract
Yasser Hassan, Carleton University
Observing drivers as they travel along relatively long study areas , such as the ramp proper and speed-change lane (SCL) at entrance and exit interchange ramps, has been a challenge. Exiting traditional traffic data collection technologies suffer from numerous limitations and their use at high-speed facilities such as freeways can be either difficult, costly, or risky. In this paper, a methodological framework is presented for obtaining complete trajectory of freeway vehicles over the entire stretch of a ramp segment in a safe, efficient , and reliable manner using UAVs and video processing. The extraction of vehicle’s trajectories from the UAV footages was done in three steps using a combination of semi and automated approaches employing different software packages. The proposed methodology was verified with speed data acquired from differential GPS receivers using three different error metrics. The results revealed that the proposed methodology offers a great promise in providing reliable and comprehensive microscopic traffic data at ramp terminals including the ramp and speed change lane, which would help researchers to fill existing knowledge gaps about driver merging and diverging behavior and its interaction with the geometry of freeway ramps and terminals.
An Experimental Investigation into Driver Behavior along Curved and Parallel Diverging Terminals of Exit Interchange Ramps
Alberto Portera, Politecnico di TorinoShow Abstract
Marco Bassani (email@example.com), Politecnico di Torino
Current design manuals indicate how to design exit ramps to guarantee comfortable and safe operations, suggesting that interchanges should be built along straight roadway sections. These criteria may prove ineffective in situations where there is no alternative to terminals being located along curved motorway segments. The paper investigates driving behavior along parallel deceleration curved terminals, with particular attention paid to the difference in impact between terminals having a curvature which is the same sign as the motorway segment (i.e. egg-shape design), and those having an opposite curvature (i.e. S-shape design). A driving simulation study was set up to collect longitudinal and transversal driver behavioral data in response to experimental factor variations. Forty‑eight drivers representing the Italian population were stratified on the basis of age and gender, and asked to drive along three randomly assigned circuits with off-ramps obtained by combining experimental factors like motorway radius (2 values), ramp length (3), curve direction (2) and traffic conditions (2). The freeway radius was found to be significant for drivers’ preferred speed when approaching the terminal. Terminal length and traffic volume do not have any significant impact on both longitudinal and transversal driver outputs. However, the effect of curve direction was found to be significant, notably reverse terminals which do not compel drivers to select appropriate speeds and lane change positions. In conclusion, the fact that this terminal type can give rise to critical driving situations is a factor that should be considered at the design stage to adopt appropriate safety countermeasures.
Understanding How Drivers Accelerate on Interchange Acceleration Lanes
Essam Dabbour, Advantage Forensics Inc.Show Abstract
Olaa Dabbour, Ryerson University
Current geometric design guide in the United States presents design values for the required lengths of interchange acceleration lanes that are based on research studies conducted in the 1950’s. To update those design values, we need to understand how current drivers accelerate on interchange acceleration lanes based on actual driver behavior patterns and vehicle mechanical characteristics. This paper presents statistical models that describe acceleration behavior of light-duty vehicles on interchange acceleration lanes based on field data collected using Global Positioning System (GPS) data logging devices that recorded the positions and the instantaneous speeds of 32 light-duty vehicles piloted by 32 drivers. The models were validated by collecting more data from 12 other drivers in a different country to ensure that the models are stable and robust when being validated with data not used in the calibration process. Updated design tables were created based on the developed models to help designers select the required length of the acceleration lane based on the design speeds of the freeway and the entrance ramp.
Impact of Geometry and Operations on Left Turn Gap Acceptance at Intersections with Permissive Indication
Boris Claros (firstname.lastname@example.org), University of Wisconsin, MadisonShow Abstract
Madhav Chitturi, University of Wisconsin, Madison
Andrea Bill, University of Wisconsin, Madison
David Noyce, University of Wisconsin, Madison
Critical and follow-up headways are the foundation for estimating the saturation flow of permissive left turns at signalized intersections. Current critical and follow-up headways recommended in the 2016 Highway Capacity Manual (HCM) are based on limited data collected from five intersections in Texas in the 1970s. This study analyzed over 2,500 left-turning vehicles at 45 intersection approaches, provides insights into gap acceptance parameters, and evaluates the effect of different site-specific factors. Video data were collected and processed from different geographical regions in the United States—Arizona, Florida, North Carolina, Virginia, and Wisconsin. Using the Maximum Likelihood method to estimate gap acceptance parameters, the mean critical headway was 4.87 seconds and the mean follow-up headway was 2.73 seconds. To account for site-specific characteristics, effect of several geometric and operational variables on critical and follow-up headway were explored. Through a meta-regression analysis, the posted speed limit and width of opposing travel lanes were found to have a significant effect on gap acceptance parameters. Results showed that with decreasing posted speed limit and/or width of opposing lanes, critical and follow-up headways also decrease resulting in greater saturation flows. When site-specific saturation flow estimates are compared with HCM saturation flow estimates, the differences ranged from -30% to +23%. This paper quantifies and illustrates the impact of site-specific characteristics on gap acceptance parameters and saturation flow.
Calibration and Development of Safety Performance Functions for Two-Way Stop-Control Intersections on Rural Two-Lane Highways in Louisiana
Ming Sun (email@example.com), University of Louisiana, LafayetteShow Abstract
Xiaoduan Sun, University of Louisiana, Lafayette
M. Rahman, University of Louisiana, Lafayette
Subasish Das, Texas A&M University
The first edition of Highway Safety Manual (HSM) contains a simplistic version of crash prediction model for two-way stop-controlled intersections (TWSC) on rural two-lane highways. This model considers AADT on both major and minor roads with the base conditions simply defined as no intersection skewness, no turning lanes, and no lighting. A crash modification factor (CMF) will be applied if an intersection has the conditions different from the base condition. The HSM model does not take account of curvature. It is well known that curved TWSC intersections are less safe than non-curved ones particularly on rural two-lane roadways. This paper presents the development of crash prediction models incorporating intersection geometrics for TWSC intersections on rural two-lane highways in Louisiana and comparing the results from the developed model with the calibrated HSM model. The negative binomial model was used with 5,126 TWSC intersections verified one by one including both three- and four-leg intersections from all parishes (counties). The estimation results indicate that AADT, curve radius, and intersection skewness angle have a significant impact on expected crash frequency for both three- and four-leg intersections. Cumulative Residuals (CURE) plots, Mean Absolute Error (MAE), and Root Mean Square Error (RMSE) were used for comparative analysis of HSM models, HSM models with calibration and Louisiana-specific models. The results show that Louisiana-specific SPFs outperformed the calibrated SPFs with greater reliability. Calibration factors of 0.58 for three-leg intersections and 0.46 for four-leg intersections are estimated, suggesting that the original HSM model overpredicts crashes in Louisiana.
Speeds of Right-Turning Vehicles at Signalized Intersections during Green or Yellow Phase
Kay Fitzpatrick (K-Fitzpatrick@tamu.edu), Texas A&M Transportation InstituteShow Abstract
Michael Pratt, Texas A&M University
Raul Avelar, Texas A&M Transportation Institute
The operation and design of signalized intersections involves tradeoffs between operational efficiency and safety for a variety of users, including motorists, pedestrians, and bicyclists. Additionally, the mix of vehicle types in the fleet sometimes requires special considerations. These concerns especially apply to the selection of curb radius at the corners, where right-turning vehicles operate in close proximity to pedestrians. Larger curb radii accommodate the swept paths of trucks and allow right turns to occur at higher speeds but may compromise safety and security for pedestrians by increasing the crossing distance and increasing the frequency of higher-speed turns.The authors collected right-turn vehicle speeds at 31 urban signalized intersection approaches in Texas with radii ranging from 15 to 75 ft. The authors calibrated a model to predict right-turn speeds as a function of site characteristics including curb radius, leading headway, vehicle type (car versus truck), maneuver of the preceding vehicle (through versus right turn), and signal indication (yellow or green). The analysis results indicate that right-turn speeds increase slightly with increasing radius, if the preceding vehicle proceeds through (rather than turning right) at the intersection, or if the signal indication is yellow rather than green. The calculated 85th percentile turning speed is generally higher than the assumed speed calculated using the radius of curvature equation. These trends should be considered if the intersection is expected to have notable volumes of pedestrians or trucks, as lower speeds are desirable for pedestrian safety, but larger radii may be necessary to accommodate turning trucks.
Evaluation of a New Intersection Design “Shifting Movements”
Ma'en Al-Omari, University of Central FloridaShow Abstract
Mohamed Abdel-Aty, University of Central Florida
Several unconventional designs have been suggested to enhance traffic operation and safety at intersections. However, the operational benefits of implementing some of them are achieved only under certain traffic conditions. For instance, the operational performance of the restricted crossing U-turn (RCUT) intersection design manifests only under highly unbalanced traffic conditions. The RCUT intersection outperforms conventional intersections that are subjected to high major traffic and light minor traffic volumes, while its operational performance fades at intersections with moderate to heavy minor road traffic. In this technical paper, a new innovative 4-leg intersection design has been proposed to replace the RCUT implementation under moderate and heavy minor road traffic volume. The new intersection design which has been named “Shifting Movements” (SM) intersection has a low number of conflict-points compared to conventional intersections, but similar to the RCUT. Therefore, similar safety benefits are expected to be achieved by the implementation of the SM intersection. Operation evaluation and comparison between conventional, RCUT, and SM intersections have been conducted in the microscopic simulation environment. Different traffic volume levels and left-turn proportions have been assumed to represent the peak hour with moderate to high left-turn traffic. The results indicated that the SM intersection design significantly outperforms conventional and RCUT intersections that are subjected to high traffic volumes in terms of average control delay and throughput. Four hundred ft. for the side street length is sufficient at the SM intersection design, while 500 ft. length is recommended for very heavy traffic volumes.
Analysis of Passing Sight Distance for a Two-Lane Highway Using Vehicle Dynamics Simulation
Abhishek Raj, Indian Institute of Technology, MadrasShow Abstract
Parth Deshpande, Indian Institute of Technology, Madras
Bhargava Chilukuri, Indian Institute of Technology, Madras
Shankarram Subramanian, Indian Institute of Technology, Madras
Passing Sight Distance (PSD) is crucial in the design of undivided two-lane highways. It has major implications on the safety and operational efficiency of roads. Existing PSD standards and models are based on simplistic assumptions and incorporate minimal road and vehicle characteristics. This research evaluates the adequacy of PSD standards in practice by comparing them with more realistic values from IPG CarMaker®, a commercial vehicle and traffic simulation software. Similar test variables are chosen to ensure an identical comparison between the simulation and standards. Additionally, the effect of the road gradient and road-tire friction on PSD is also analyzed by configuring the parameters in the simulation. High deviations of up to 52% are observed in the PSD values when compared to existing standards under different road conditions. In the latter half of the paper, an analytical model for PSD is proposed. This model allows the selection of parameters as well as the application of physical vehicle constraints. The deviations observed in PSD values obtained from this model are lower than 5% for the specified test cases simulated in the vehicle dynamics simulator and signify the importance of considering the microscopic behavior of a vehicle during a passing maneuver.
Studying the Dynamic Sight Distance Problem with a Machine Learning Algorithm
Manoj Jha, MKJha ConsultingShow Abstract
Hellon Ogallo, Maryland State Highway Administration
The Dynamic Sight Distance (DSD) problem involves the dynamically allocated sight distance as a left-turning vehicle makes it move to clear a signalized intersection during the permissive phase whose line-of-sight is obstructed from the presence of stationary vehicles in opposing left-turning lanes. In this paper we study the DSD problem with a Machine Learning (ML) algorithm called Random Forest (RF) classifier. In our previous works we used limited field data to measure gap sizes and a driver’s willingness to accept or reject critical gaps to formulate the DSD problem; and calculated the probability of line-of-sight in the analysis. Field data from 10 signalized intersections from Maryland with unprotected left turns were used in the study. This paper extends the previous methodology by introducing additional variables attributed to gap acceptance, such as obstruction angle, driver’s age, number of queued vehicles, and presence or absence of a peak hour. The results show that presence or absence of peak hour and number of queued vehicles are highly correlated to the driver’s decision-making in accepting or rejecting a gap. Several simulation runs are conducted to improve the accuracy of the model. We conclude that the RF classifier is highly effective and better than traditional Raff’s method in predicting a driver’s behavior to accept or reject a gap associated with the DSD problem. Future works may include extending the methodology for arterial network with many signalized intersections with DSD issues, traffic signal optimization, simulation related studies, Vehicle to Vehicle communication, and Vehicle Infrastructure Integration.
Develop a Google Earth-Based Method to Measure Sight Distance for U-turns at Unsignalized Intersections on Multilane Divided Highways
Li Quan (Lzq0007@tigermail.auburn.edu), Auburn UniversityShow Abstract
Beijia Zhang, Auburn University
Huaguo Zhou, Auburn University
The U-turn, as an alternative to a direct left turn, is one of the most popular access management techniques implemented by many state transportation agencies, sight distance (SD) is one of the major safety concerns for U-turn movement. The traditional method of measuring the SD is using sight rods in the field, which is inconvenient and unsafe; thus, it is important to develop a convenient method to measure SD for U-turn movement. The objective of this study is developing a safe and cost-effective method to measure SD and locate positions where have SD issues without going to the field for U-turns vehicles using tools in the Google Earth and a perspective grid that can be generated by Kinovea software. The methods can estimate the U-turn SDs for these two different road geometric conditions: i) a straight segment with crest curves; and ii) a roadway segment with a combination of crest curve and horizontal curve. For Condition i, a SD equation as a function of distance and elevation measured in Google Earth was developed. For Condition ii, a perspective grid was first applied on Google Earth Ground-Level view; then, the number of broken lines and gaps in each perspective grid cell were used as references to measure the SDs. All inputs can be collected using Google Earth. The field measurements of U-turn SDs at ten locations were conducted to verify method’s results. The results showed that the differences between the model measurements and field measurements are all less than 10%.
Super 2 Passing Lane Design: Operational and Economic Benefits
Marcus Brewer, Texas A&M Transportation InstituteShow Abstract
David Florence, Texas A&M Transportation Institute
Brianne Glover, Texas A&M Transportation Institute
Kay Fitzpatrick, Texas A&M Transportation Institute
Steven Venglar, Texas A&M Transportation Institute
Timothy Barrette, Texas A&M Transportation Institute
Super 2 corridors with passing lanes provide operational benefits to traditional two-lane highways by creating passing opportunities and reducing delay and crashes, leading to increased use of Super 2 corridors across Texas. However, as more passing lane length is added, the more it may resemble a traditional four-lane alignment and reduce the unique benefits of a Super 2. Recent research investigated operational and economic benefits of Super 2 corridors compared to traditional four-lane and two-lane cross-sections. Researchers analyzed the operational performance of a simulated 40-mile corridor with varying average daily traffic (ADT); heavy vehicle volumes; and length, number, and spacing of passing lanes to identify benefits in key scenarios. Operational and benefit-cost inputs formed the basis of a model to quantify the relative economic benefits of Super 2 corridors. Operational analysis showed that, at volumes up to 17,000 vehicles per day, Super 2 cross-sections provided higher average minimum speeds and lower delay than other options with less than four lanes, though the two-lane cross-section with left-turn lanes had similar performance as Super 2 for volumes of 15,000 vehicles per day or higher. Economic analysis showed that Super 2 had the highest benefit-cost ratios in all scenarios. In both the economic and operational analyses, the findings agreed with previous research that adding shorter passing lanes to a Super 2 corridor is more beneficial than providing fewer but longer passing lanes.
Transferability of Crash Modification Effects via Graphical Causal Models: Application to Sight Distance and Left-Turn Lane Offsets
Gary Davis (firstname.lastname@example.org), University of Minnesota, Twin CitiesShow Abstract
Safety-based roadway design requires predictions of a design’s safety consequences. In the USA, the tools for making these predictions are essentially empirical summaries of the driver and vehicle mix prevalent during the last 20 years or so, which are likely to change as vehicle automation becomes widespread. A major challenge facing safety researchers will then be to adapt, if possible, this extensive existing research to new and different conditions. This paper presents an exploratory investigation into how Bareinboim and Pearl’s tools for “transportability” analysis can be used to adapt existing safety knowledge to new situations. Analytic results are presented and then applied to the problem of transporting a crash modification factor, associated with a change in left-turn lane offset, from a situation where no vehicle automation is present to a new situation containing vehicles equipped with automated emergency braking. Such analyses are feasible, when one has at hand a quantitative explanation of how a safety-related modification achieves its effect.
Automatic Identification of Roadway Horizontal Alignment Information Using GIS Data: CurvS Tool
Bekir Bartin (email@example.com), Ozyegin UniversitesiShow Abstract
Sami Demiroluk, AgileAssets, Inc.
Kaan Ozbay, New York University
Mojibulrahman Jami, Ozyegin Universitesi
This paper demonstrates CurvS , a web-based tool to allow researchers and analysts to automatically extract, visualize and analyze roadway horizontal alignment information using readily available GIS roadway centerline data. The functionalities of CurvS are presented along with a brief background on its methodology. The validation of its estimation results are presented using actual horizontal alignment data from two different roadway types, Route 83, a two-lane two-way rural roadway in New Jersey and I-80, a freeway segment in Nevada. Different metrics are used for validation. These are identification rates of curve and tangent sections, overlap ratio of curve and tangent sections between estimated and actual horizontal alignment data, and percent fit of curve radii. The validation results show that CurvS is able to identify all the curves on these two roadways, and the estimated section lengths are significantly close to the actual alignment data, especially for the I-80 freeway segment, where 90 percent of curved length and 94 percent of tangent section length are correctly matched. Even when curves have small central angles, such as the ones in Route 83, CurvS ’s estimations covers 71 percent of curved length and 96 percent of tangent section length
Study on Minimum Radius of Horizontal Curves of Two-Lane Highways in Plateau Area Based on Drivers' Psychological and Physiological Characteristics
Fei Hu, Southeast UniversityShow Abstract
Fei Chen (firstname.lastname@example.org), Southeast University
Jingyi Zheng, Southeast University
Yunlong Zhang, Texas A&M University, College Station
Wu Bo, Tibet University
Ping Zhang, Tibet University
The special natural and geographical environment in high altitude areas has a significant influence both on the physiological and psychological status of drivers, inducing the raise of the workload of drivers, which could negatively affect driving safety. Therefore, it is of great significance to consider the impact of hypobaric hypoxic conditions on drivers when researching the minimum radius of the horizontal curve which applied to two-lane highways of the plateau. The section from Nyingchi to the Mountain Shegyla on G318 is selected as the experimental road for field experiment. Besides, the model for simulated experiment is established by UC/Win Road, in order to exaggerate the ESS (Effective Sample Size). By adopting the Paired Sample T-test, the consistency of the field and simulated experiments is confirmed. Sample entropy is adopted to process the collected data, including the speed of the vehicle, HR, and EEG of the driver. Additionally, PCA (Principal Component Analysis) is applied to evaluate the comprehensive index CISE, which comprehensively represented the psychological and physiological load of drivers. Subsequently, the correlations between CISE with speed and radius of the horizontal curve at different altitudes is analyzed, verified that lateral acceleration is found to be the index of the greatest influence on CISE, from the perspective of driving dynamics. Values of minimum radius of horizontal curve of two-lane highways in plateau area were proposed to amend the current version of Design Specification for Highway Alignment .
Development of a New Intelligent Speed Adaptation System Based on Available Sight Distance to Promote Safe Speed Decisions along Highways.
Abrar Hazoor, Politecnico di TorinoShow Abstract
Alessandra Lioi, Politecnico di Torino
Marco Bassani (email@example.com), Politecnico di Torino
Highways and streets are designed without considering the improved performance of modern vehicles and the new onboard technologies available for assisted driving. Consequently, vehicles may travel at speeds which are substantially higher than the maximum considered in road design criteria. Hence, the need for speed and safety related countermeasures (e.g., field control, mobile or fixed speed cameras, traffic calming measures). However, such countermeasures are proving ineffective, and the proportion of speed‑related crashes to total crashes remains significant. This investigation is aimed at the development of a new Intelligent Speed Adaptation (ISA) system based on the available sight distance (ASD). The aim of the system is to inform drivers when they are travelling at inappropriate speeds, generate warning sounds to the same effect and, if necessary, intervene directly to compel drivers to adopt the speed which is most appropriate to the particular ASD. In this methodological paper, the functionality of the new ISA system has have been tested at the driving simulator of the Politecnico di Torino (Italy). The estimation in the virtual environment of the ASD has been validated and tested with successful results. Future experimental investigations will be devoted to assessing the effectiveness of the system on driver speed behavior.
Examination of Features Correlated with Roadway Departure Crashes on Rural Two-Lane Roads
Justice Appiah (Justice.Appiah@VDOT.Virginia.gov), Virginia Transportation Research CouncilShow Abstract
Mo Zhao, Virginia Transportation Research Council
Roadway departure (RD) crashes are one of the major causes of fatalities on highways. Reducing the number and severity of RD crashes is one of the emphasis areas of the strategic highway safety plan for many state departments of transportation in the United States. Many significant efforts have been aimed at reducing RD crashes, and a continued focus on preventing these crashes is needed. The purpose of this study was to identify roadway geometric design, roadside, and traffic characteristics that are correlated with RD crashes on rural two-lane roads. Using data collected in Virginia from 2014-2018, this study analyzed the characteristics of RD crashes on rural two-lane roadways and identified how the variation in RD crash frequency is related to roadway, roadside, and traffic features. There were several key findings: (i) shoulder width was significantly associated with RD crash frequency, and locations with narrower shoulders were more likely to have more RD crashes; (ii) roadway curvature was significantly associated with RD crash frequency, and locations with horizontal curves were more likely to have frequent RD crashes; and (iii) locations with narrow shoulders and high speed limits were more prone to RD crashes.
Evaluating the Impacts of Speed Limit Increases on Rural Two-Lane Highways using Quantile Regression
Md Shakir Mahmud, Michigan State UniversityShow Abstract
Nischal Gupta, Michigan State University
Babak Safaei, Michigan State University
Hisham Jashami, Michigan State University
Timothy Gates, Michigan State University
Peter Savolainen, Michigan State University
Eva Kassens-Noor, Michigan State University
Understanding speed selection behavior of drivers following speed limits increases is critically important. To date, the literature has largely focused on freeways and the effects of speed limit changes on two-lane highways remains under researched. Prior research has also generally focused on changes to mean speeds, though the speeds of both the highest and lowest drivers are also of great interest. This study investigates trends in free-flow travel speeds following 2017 legislation that increased the posted speed limit from 55 to 65 mph on 943 miles of rural highways in Michigan. Speed data were collected for over 46,000 drivers at 67 increase segments and 28 control segments, where the speed limits remained unchanged, before and during each of the two successive years following the speed limit increases. Site-specific traffic, geometric, and cross-sectional information was also collected. The impacts of the speed limit increases on the 15th, 50th, and 85th percentile speeds were evaluated using quantile regression. Separate analyses were conducted for passenger cars and heavy vehicles. Locations where the speed limits were raised experienced increases in travel speeds ranging from 3.8 to 5.1 mph. The control sites experienced marginal changes in speeds, which suggests any spillover effects of the higher speed limits have been limited. Significant differences were observed across the quantiles with respect to the effects of the speed limit increases, as well as numerous site-specific variables of interest. The results provide important insights as to the nature of driver speed selection and the impacts of speed limit increases.
Lessons Learned In Roadway Design: A Few Nuggets Of Knowledge
David McDonald, Hanson Professional Services, Inc.Show Abstract
With senior roadway design staff approaching retirement and 50% of the workforce to be millennials by 2020 (1), there are many design experiences that should be passed on to the next generation of roadway engineers and designers. It is important that this knowledge transfer occurs so the next generation of engineers can learn to minimize the number of design challenges they may experience. If some of these challenges can be reduced or avoided, the engineers can focus on reaching a beneficial design with fewer difficulties. This paper examines lessons learned in roadway design from the perspective of a chief roadway engineer and includes understanding design criteria, horizontal geometrics, combined geometrics, coordination with other disciplines, maintenance of traffic (MOT), plan production, and designing roads for the future.
SYSTEMATIC SAFETY EVALUATION OF DIVERGING DIAMOND INTERCHANGES BASED ON NATIONWIDE IMPLEMENTATION DATA
Ahmed Abdelrahman, University of Central FloridaShow Abstract
Mohamed Abdel-Aty, University of Central Florida
Jinghui Yuan, University of Central Florida
Ma'en Al-Omari, University of Central Florida
Diverging Diamond Interchanges (DDIs) are designed as an alternative to the conventional diamond interchange to enhance the operational and safety performance as they have a lower number of traffic conflict points. Since drivers are not familiar with DDIs’ operation, which results in many wrong-way maneuvers, there is a need to evaluate the safety performance of this type of interchanges to validate their effect, and to estimate reliable and representative Crash Modification Factors (CMFs). This paper evaluates the safety of DDIs using three methods, which are before-and-after study with comparison group, Empirical Bayes before-and-after method, and cross-sectional analysis. This study was conducted based on a nationwide sample of 80 DDIs in 24 states. The analysis results indicated that converting conventional diamond interchange to diverging diamond interchanges could significantly decrease the total, fatal-and-injury, rear-end, and angle/left turn crashes by 14%, 44%, 11%, and 55%, respectively. Moreover, the developed safety performance functions (SPFs) implied that two types of geometric characteristics (i.e., the distance between crossovers/ramp terminals and freeway exit ramp speed limit) have the potential to reduce the frequency of specific crash types. The study contributes to the existing literature by using a relatively large representative sample size, which provides more statistically significant safety measures. In addition, this study also explored the effects of different traffic and geometric characteristics on the safety performance of DDIs.
Considering Roadway Context in Setting Posted Speed Limits
Kay Fitzpatrick (K-Fitzpatrick@tamu.edu), Texas A&M Transportation InstituteShow Abstract
Subasish Das, Texas A&M University
Timothy Gates, Michigan State University
Karen Dixon, Texas A&M University
Eun Sug Park, Texas A&M University
The National Cooperative Highway Research Program (NCHRP) Project 17-76 investigated factors that influence operating speed and safety through a review of the literature and an analysis of the relationships for speed, safety, and roadway characteristics on urban/suburban streets. That knowledge along with a review of existing speed limit setting practices was used to develop a Speed Limit Setting Procedure (SLS-Procedure) along with a user manual to explain the SLS-Procedure. In addition, the SLS-Procedure was automated via a spreadsheet-based Speed Limit Setting Tool (SLS-Tool). These products will permit engineers to make informed decisions about the setting of speed limits. The SLS-Procedure is fact based and transparent relying on a set of decision rules that consider both driver speed choice and safety associated with the roadway. The SLS-Procedure was designed to be applicable across different roadway types and contexts by having a set of unique decision rules for four combinations of roadway types and contexts: limited-access, undeveloped, developed, and full-access facilities. The SLS-Procedure uses the operating speed distribution as a reference for the suggested speed limit, with the resulting suggested value based on consideration of roadway type, context, safety performance, and other characteristics.
Safety Performance of Crossroad Ramp Terminals at Single-Point and Tight Diamond Interchanges
Darren Torbic, Texas A&M Transportation InstituteShow Abstract
Richard Porter, VHB
Jeff Gooch, VHB
Kristin Kersavage, VHB
Single-point diamond interchanges and tight diamond interchanges are two alternative interchange types that are considered in urban areas where right-of-way is usually limited. The Highway Safety Manual (HSM) predictive methods for freeways and interchanges could currently address freeway mainline, freeway-ramp terminal, and ramp proper safety performance associated with these interchange types. However, limited research has been conducted to compare the safety performance of the crossroad ramp terminals for these two alternative interchange designs, as would be necessary fora performance-based approach to interchange alternatives analysis. Planners, designers, and safety managers would benefit by having tools to compare the safety performance of these crossroad ramp terminals to make more informed decisions regarding their use and application in the urban environment. Research was undertaken with the objective to develop new intersection crash prediction models for crossroad ramp terminals at single-point diamond interchanges and crossroad ramp terminals at tight diamond interchanges. In general, it was found that the crash prediction models for crossroad ramp terminals at single-point diamond interchanges predict more crashes than the models for crossroad ramp terminals at tight diamond interchanges in higher volume conditions. The differences are primarily driven by the property-damage-only crash models. Comparisons of the crash prediction models suggest that the two sets of models appear compatible and provide reasonable results over the range of applicable traffic volume conditions.
Curbside Management Challenges and Opportunities: Insights from the Public and Private Sectors in 14 US Cities
Caleb Diehl, University of WashingtonShow Abstract
Andisheh Ranjbari, University of Washington
Anne Goodchild, University of Washington
With spikes in on-demand delivery, ridehailing, and shared mobility use, cities are observing dramatic increases in demand for curbspace. In response, cities and private companies have proposed a diverse range of structural, policy and technology solutions to more efficiently manage the curb lane. Through structured interviews with public agency and private company staff and a review of existing pilot project evaluations and curb management guidelines, this study surveys contemporary approaches to curbside management in 14 U.S. cities. A total of 22 staff from public works departments, transportation agencies, and Metropolitan Planning Organizations (MPOs) in every census region of the United States were interviewed. Representatives of nine technology companies were also interviewed regarding the opportunities and challenges for curb management tools, including smart parking reservation systems, occupancy sensors and cameras, automated enforcement, and common data standards. The results show that the top curb management concerns among public officials are enforcement and communication, data collection and management, and inter-agency coordination. Interviewees reported success with policies such as passenger pick-up and drop-off (PUDO) zones, incentives for off-peak delivery, and requiring shared mobility data in exchange for reservable or more loading zones. Both public and private sector staff expressed a desire for citywide policy goals around curb management, more consistent curb regulations across jurisdictions, and a common data standard for encoding curb information.
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