Highway Facilities Research Articles

50th Anniversary Invited Article—Autonomous Vehicles and Connected Vehicle Systems: Flow and Operations Considerations

The impacts of autonomous vehicles, coupled with greater inter-vehicle and system connectivity, may be far-reaching on several levels. They entail changes to (1) the demand and behavior side, (2) the supply of mobility services, and (3) network and facility operational performance. We focus here on their impact on traffic flow and operations, especially in mixed traffic situations in which autonomous vehicles share the road with regular, human-driven vehicles, along with connected vehicles that may also have some automated functions. These mixed traffic situations correspond to likely deployment scenarios of the technologies, especially in the long transition towards 100% deployment. We explain using elementary traffic science concepts how autonomous vehicles and connected vehicles are expected to increase the throughput of highway facilities, as well as improve the stability of the traffic stream. A microsimulation framework featuring varying behavioral mechanisms for the three classes of vehicles is introduced. The framework is used to examine the throughput and stability questions through a series of experiments under varying market penetration rates of autonomous and/or connected vehicles; at low market shares, the impacts are relatively minor on either throughput or stability. However, as market shares increase, autonomous vehicles exert a greater influence on both dimensions compared to the same shares of connected vehicles. Applications of the framework to examine the effectiveness of selected traffic management approaches are discussed, including dedicated lanes for autonomous vehicles (good only if its use is optional and when the market share of autonomous vehicles is greater than the percentage of nominal capacity represented by that lane), and speed harmonization.

Comparison of travel time measurement methods along freeway and arterial facilities

Travel time is an important performance measure used to assess traffic operational quality of various types of facilities. Previous efforts to estimate travel time have also compared model-estimated travel times to field-measured travel times using various sources of data. Given the variety and diversity of travel time measurement methods, it is important to evaluate the accuracy of the data obtained by each of them and to develop recommendations regarding their suitability in the validation of travel time estimation models. The research objective for this paper was to collect field data along several freeways and arterials and to evaluate the travel times obtained by STEWARD (Statewide Traffic Engineering Warehouse for Regionally Archived Data), INRIX, BlueTOAD (Bluetooth Travel-time Origination and Destination), and HERE. Benchmark data were collected with the use of an instrumented vehicle at five freeway segments and two arterial segments in Florida. The field-measured travel times were statistically compared with the travel times provided through various methods. The results suggest that the HERE traffic data provide better freeway travel time estimates compared to the remaining methods. In oversaturated conditions, STEWARD, INRIX and BlueTOAD data seem to underestimate travel times, while HERE data were found to be more accurate. For undersaturated freeways, STEWARD, INRIX and BlueTOAD were found to perform better than HERE. At the arterial sites BlueTOAD and HERE travel time data were analyzed and the analysis suggests that none of the methods is accurate, possibly due to the small sample size.

Development of operating mode distributions for different types of roadways under different congestion levels for vehicle emission assessment using MOVES

ABSTRACTThe Motor Vehicle Emission Simulator (MOVES) quantifies emissions as a function of vehicle modal activities. Hence, the vehicle operating mode distribution is the most vital input for running MOVES at the project level. The preparation of operating mode distributions requires significant efforts with respect to data collection and processing. This study is to develop operating mode distributions for both freeway and arterial facilities under different traffic conditions. For this purpose, in this study, we (1) collected/processed geographic information system (GIS) data, (2) developed a model of CO2 emissions and congestion from observations, (3) implemented the model to evaluate potential emission changes from a hypothetical roadway accident scenario. This study presents a framework by which practitioners can assess emission levels in the development of different strategies for traffic management and congestion mitigation.Implications: This paper prepared the primary input, that is, the operating mode ID distribution, required for running MOVES and developed models for estimating emissions for different types of roadways under different congestion levels. The results of this study will provide transportation planners or environmental analysts with the methods for qualitatively assessing the air quality impacts of different transportation operation and demand management strategies.

The effect of Design Guideline for Expressway Facilities

Background The purpose of this study is to analyze the preference for highway facilities using before and after images and to assess the satisfaction of highway facilities. Throughout this process, the study shows the effectiveness of a public design guideline for highway facilities by the Korea Expressway Corporation. Methods The before images show the current facilities and the simulated after images represent the facilities that follow the public design guideline. The assessment is analyzed by the t-test and analysis of variance (ANOVA) test. Results The study found that the highway facilities with a public design guideline were mostly upgraded and the difference between the before and after images was considered statistically significant. Especially, all after images were valued over 4 in every assessment. Also, this study shows that there can be a difference of perception on a project between experts and common users. Thus, a public design guideline should be examined from the users’ point of view for practicality and usefulness. Conclusions The results of this study prove the effectiveness of a public design guideline and help implement an improvement project with guideline sustainability. Moreover, the results make it possible to analyze each facility characteristic and arrange specific management practices for highway facilities.

Toward an operating speed profile model for rural two-lane roads in Egypt

The geometric design, especially the horizontal and vertical alignments, of rural two-lane highway facilities is considered one of the most important factors affecting the quality of traffic service and safety. A consistent highway geometric design is defined to be one that conforms to the driver's expectations. In order to calculate the main measures of design consistency, an accurate operating speed profile model for road alignment is needed. Studies have shown that operating speed models are country dependent due to varying demographics, driver attitudes, habits, etc. This paper develops a speed profile model for two-lane rural roads in Egypt. This includes the development of operating speed models for horizontal curves and tangents, as well as the study of the characteristics and relationships between acceleration and deceleration rates before and after horizontal curves. The study uses a desert rural two-lane, two-way road sections that connect the city of Sohag with the city of Hurghada, in Upper Egypt. All geometric characteristics were obtained from highway authority. Speed data regarding individual drivers traveling on selected two-lane rural road sections were sampled using an on-board GPS system. The study confirms the finding in previous research that curvature is the most important factor in determining the speed on horizontal curves. Moreover, tangent length is the most important factor in determining operating speeds at tangents. The acceleration and deceleration characteristics were derived to gain an understanding of the behavior of individual vehicles traveling through curves of varying radii and lengths as well as preceding tangent length. Several operating speed models were developed for tangents and curves as well as for acceleration and deceleration rates. Incredibly effective, these models can be used for design consistency evaluations.

Enhanced Decision-Making Framework Using Reliability Concepts for Freeway Facilities

This paper presents a decision-making framework based on a travel time reliability methodology developed under the U.S. Strategic Highway Research Program. Existing methods consider a set of predefined prevailing conditions for the analysis of freeway facilities as the base case. However, a reliability analysis accounts for multiple recurring and nonrecurring congestion sources to estimate the travel time distribution over a long time horizon. This approach considers variations in traffic demand levels, inclement weather conditions, and incidents that occur stochastically on a freeway facility. Several performance measures are defined based on the travel time distribution, which comprehensively cover the full range of operational conditions on the system. Based on the proposed decision-making framework, mobility strategies can be identified, evaluated, and improved.

Development of Software Application for Nigerian Traffic Flow Monitoring and Prediction of High-Way Infrastructural Facilities

Development of Software Application for Nigerian Traffic Flow Monitoring and Prediction of High-Way Infrastructural Facilities

Development of a Mobility-Based Service Measure for Freeway Facilities

The Highway Capacity Manual (HCM) currently uses a bipolar approach to defining level of service (LOS) for freeway facilities: either (1) weighted density or (2) assigning LOS F if one or more segments experience LOS F. The major shortcoming of this approach is that density is a poor indicator of travelers’ experiences under congested conditions; speeds or travel times are more relevant to travelers and are consistent with how agencies measure and report congestion using field data. Likewise, saying a facility operates at LOS F if one only segment experiences LOS F is misleading. Further, five of the six LOS ranges exist where speeds are relatively high (above approximately 50 mph) and only one LOS range is used to define the congested regime, which is of the highest interest in large urbanized areas. Especially with regard to operations improvements, many congestion management techniques will improve congestion (e.g., delay) but the facility will still be classified as LOS F under the current definition.This paper deals with this issue by defining a travel time-based service measure for freeway facilities. Two HCM applications are explored: (1) traditional(static) freeway analysis and (2) the new travel time reliability (TTR) analysis procedure. Several performance measures are explored for the service measures by analyzing field data from seven U.S. urban areas. Although the research is not complete as of this writing, the mean travel time index is probably the best measure for the static procedure and either the 80th or 95th percentile travel time index should be used with the reliability procedure. Analysis of field data revealed strong correlation between the mean and upper percentiles of the travel time distribution, so these measures are internally consistent.A shift away from the current density-based LOS structure is recommended. The new structure uses ranges of the selected travel time measures that indicate different levels of the user experience. This approach is similar to what is done in the HCM for urban streets. Reconciling LOS concepts between freeways and urban streets will make the HCM more usable for the emerging field of performance management.It is recommended that travel time reliability be the service measure for freeway facilities which are part of an extensive freeway network in large urbanized areas, those over 500,000 population. An extensive freeway network is defined as having at least three freeway facilities. Analysts should use their judgment in cases that do not meet these Density would continue to be used on all other freeway facilities as well as for other aspects of freeways covered by the HCM (e.g., freeway segments).Recognizing that agencies may want to define their own service standards, a procedure for setting locally-defined standards is developed, based on the steps used in this research.It is expected that the freeway facility service measures will be an aid in setting transportation system and freight performance targets, a a demonstration of how they would be used for target setting is presented.

A Rationale for Enhancing the German Highway Capacity Manual to Incorporate Oversaturated Freeway Facility Analysis

Unlike the U.S. 2010 Highway Capacity Manual, the most recent edition of German Highway Capacity Manual does not include methodology to evaluate the facility within oversaturated time periods. To incorporate this traffic flow regime within the methodology, we identify several aspects of the methodology that require enhancements and propose modifications. Next, we implement these modifications in a macroscopic traffic model developed as a software implementation of the German guideline. In this manner, the HBS user can conduct traffic flow analysis that includes volume-to-capacity ratios above 1.00 which has not been foreseen by the guideline until now. The main contribution of this paper is the identification of methods within the German Highway Capacity Manual that require modification to enable incorporation of oversaturated traffic flow within the analysis. Further, we introduce traffic density as a variable within the HBS methodology and show benefits of its incorporation during the oversaturated time periods. Finally, the paper includes illustrative examples of empirical and model-based evaluation of congested freeway facility in Germany. The paper concludes with a discussion of proposed methods and their limitations.

Assessment of Level-Of-Service for Freeway Segments Using HCM and Microsimulation Methods

The Highway Capacity Manual (HCM) 2015 freeway facilities methodology offers a supplemental computational engine FREEVAL, which is a macroscopic/mesoscopic tool that enables users to implement HCM-based freeway analysis quickly and conveniently. On the other hand, Vissim is a microscopic simulation tool that enables users to model real-world conditions with high level of accuracy and comprehensiveness. Thus, the two tools represent quite opposite sides in freeway modelling – Vissim requires time-consuming preparation and calibration of the model but it usually provides benefits that are more comprehensive. FREEVAL requires less on input and calibration sides but its results may not be as beneficial as comprehensive and accurate as Vissim’s. The problem, that has not been addressed enough, is that we do not know how different their results are (when compared between themselves) and, at the same time, how close to the field conditions. Researchers and practitioners use both tools for freeway analysis and tend to compare the results directly. One of the commonly used performance measures is the Level of Service (LOS), which is used to quickly evaluate the freeway segment or facility performance. The HCM Freeway Facility Methodology uses density to estimate LOS. However, density is calculated differently in FREEVAL and Vissim, and comparing the estimated LOSs between the two may not represent a proper comparison. In essence, FREEVAL, in the under-saturated condition, estimates the density from the fundamental equations where the volume is estimated from the user entered demand and the speed is calculated using the statistical models provided in respective chapters of each segment type. On the other hand, Vissim tracks each individual vehicle as it moves along a freeway and calculates key performance measures by using individually modeled driver’s behavior. This paper aims to compare and contrast the methodologies behind the two tools and offer explanation and discussion of their outputs. The paper will cover four major HCM freeway segment types (basic, merge, diverge, and weaving) in under-saturated conditions. Field data will be acquired from a section of I-880 freeway in California. FREEVAL and Vissim models will be calibrated and validated using Mobile Century Data provided by University of California at Berkley and Caltrans Performance Measurement System. The output of both tools will be evaluated against the field data. The assessment should reveal the ability of each tool to replicate the real-world conditions. Paper results will contribute to the existing body of knowledge by filling the gap in the literature related to comparison and contrast of the key (LOS-related) performance measures of these two tools.

Comprehensive Evaluation of Entropy-hierarchical Grey Correlation Analysis for Highway Safety Life Protection Engineering

Different highway safety life protection engineering decision-making have important meaning. The achieving goals and optimal highway safety life protection engineering scheme can not only improve the function of the highway facilities and service level, still can reduce the traffic accident, which caused by the imperfect highway facilities. Different highway safety life protection engineering decision-making is a multiple targets, multi-layers and multi-schemes system evaluation problem. With regard to lack of concrete data on multiple targets, multi-layers and multi-schemes system evaluation problem, make analytical hierarchy process combined with the entropy value analysis into the grey relational comprehensive evaluation method, and then get entropy-hierarchical grey correlation analysis method. This method is a qualitative and quantitative decision method, which combine comparison principle of analytic hierarchy process (AHP) and the entropy principle of entropy value analysis method to determine the relative weight of various indexes between factors layer-by-layer. Then using grey relational analysis by low-layer to high-layer step by step in the possible scheme and referenced scheme. Finally, calculating the comprehensive correlation degree between the possible scheme and referenced scheme, the best plan which has maximum grey correlation degree can be selected.

The New German Highway Capacity Manual (HBS 2015)

With the introduction of the German Highway Capacity Manual (HBS) in January 2002 (FGSV, 2002), all methods for the evaluation of the performance of highway facilities were, for the first time in Germany, simultaneously updated and consolidated in a single work following the ideas of the American Highway Capacity Manual (HCM). This paper gives an overview of the new 2015 edition of the German HBS and describes the changes as for example the addition of chapters for freeway, rural roads, and major urban street facilities, comprising segments and intersections.

Estimating Drivers’ Willingness to Pay by Using Empirical Data from a Variably Priced Freeway Facility

This paper presents a simplified method for estimating the percentage of drivers who would choose to use a priced facility in place of a free alternative by means of a year of revealed preference data from a variably priced freeway facility in Southern California. The resultant model showed a strong fit to the set of 5,071 bins of data (with an R2 value of .869) while using only three easily obtained predictor variables: the expected travel time savings by use of the managed lanes, the toll price being imposed, and the relative speeds between the two alternatives at the time the decision is made. This model contrasts sharply with other existing methods of analysis, which often use logit models and require much more detail about the population of drivers. The author then illustrates how these results can be used for planning analyses of other priced facilities with different operational conditions and roadway configurations (specifically, converting a current high-occupancy-vehicle facility to a high-occupancy-toll facility) by using only the level of data that would be available from common inductive loops, subject to assumptions about the transferability and generalizability of these results from Southern California to the facility being analyzed.

Developing Analytical Procedures for Calibrating the Highway Safety Manual Predictive Methods

Performance-based safety goals and objectives are more attainable with the use of the Highway Safety Manual (HSM). However, the safety performance functions (SPFs) in the HSM may not be accurate when used with local jurisdictions. Each SPF and crash modification factor (CMF) assume a set of base site conditions that might not be realistic or representative of local highways. The calibration procedures provided in Part C, Appendix A, of the HSM should therefore be modified to accommodate local data availability as well as roadway, traffic, and crash characteristics. Furthermore, a set of base conditions applicable to local highways should be determined. Results show that the HSM models underestimate the total average number of crashes on highway segments for all rural highway facility types in South Dakota. To quantify highway safety performance better, this study analyzed the underlying factors contributing to the underestimation and proposed procedures to improve crash prediction accuracy. The HSM calibration was performed with crash data from rural two-lane, two-way highways and rural multilane divided and undivided highways during a 5-year period (2008–2012). The procedures included establishing new base conditions, developing jurisdiction-specific SPFs, and converting CMFs to new base conditions. The comparison results show that the customized models outperform the HSM models in predicting sites with crashes.

하이패스 운용가용도를 이용한 부품의 교체 추정 모델

FTMS, TCS, ITS equipment such as high-pass highway are just a situation that does not lack traceability and passive surveillance is related to fault DB has so far consisted of an integrated operations management to maximize utilization of the facility. In addition, there is no replacement parts are replaced when a failure occurs, increasing the number of parts and repair time I have trouble growing, and becoming a service interruption whenever you replace each time. In this study, proactively manage the failure history of a highway facility ITS tries to preventive maintenance. Therefore, the error history is based on the reliability of the high-pass facilities theory to calculate the reliability of the system through a systematic statistical analysis Operational Availability. The fault number and the time the replacement period through the estimate decreases and can reduce the budget expenses by securing the spare parts quantity, establish a management plan in part by improving the quality of the system through constant preventive maintenance, quality of service at all times It may direct the non-stop operation state of the available state.

Exploring Traffic Conflict-Based Surrogate Approach for Safety Assessment of Highway Facilities

This study explored potential use of a traffic conflict-based surrogate safety assessment as an alternative way of evaluating the safety performance of roads and identifying potential sites for safety improvement. The study compared two major safety assessment streams (a statistical modeling method and a traffic conflict-based method) in their evaluation of crash risk to investigate the performance of the traffic conflict-based method as an alternative to the crash-based method in identification of hot spots. The empirical Bayes (EB) method coupled with the safety performance function (SPF), called the EB-SPF method, was used as a benchmark, and the conventional crash frequency method was used as a comparison supplement. These two methods were viewed as the crash-based methods because they relied on crash data. Traffic conflicts were estimated through the microscopic traffic simulation model VISSIM. The safety evaluation was performed separately for 24 signalized intersections and 86 segments in the Tyson...

Assessment of Queue Length and Delay at Toll Plaza Using Microscopic Traffic Simulation

Highways and freeways usually experience severe traffic congestion due to the presence of toll plazas which is considered as a bottleneck. In recent years, traffic engineers around the world have utilised microscopic traffic simulation models as tools to evaluate the performance of selected freeway facilities based on known traffic pattern data. This study attempts to analyse the performance of toll plaza by utilizing the microscopic traffic simulation software VISSIM 6.0, based on two different output measures, namely: average queue length and average delay time. At the selected toll plaza, data are collected at toll booths for all three modes of payments, which are: cash mode, Touch n Go, and Smart TAG. Therefore, this study aims to build a microscopic traffic simulation model that is capable of analysing the behaviour of vehicles at toll plaza based on the mentioned output measures for each mode of payment and also to determine the type of payment mode that has the most significant impact on the overall performance of toll plazas and ultimately, to understand the causes of congestion at toll plaza.

Modeling vehicle–pedestrian interactions outside of crosswalks

Pedestrian and driver behaviors as well as their interactions, are essential in planning, designing and operating highway facilities. Pedestrian crossing outside of a marked or unmarked crosswalk (i.e. jaywalking), is one of those pedestrian behaviors that may highly affect safety and operations. Unlike permissible crossings at crosswalks, jaywalking events are not often anticipated by drivers, which may result in less driver reaction time and different vehicle operation dynamics. It is important to understand pedestrian crossing behavior outside of crosswalks, as well as driver yielding behavior towards them. To date, limited quantitative and behavioral research has been conducted to investigate this interaction or simulate it microscopically. This paper aims to explore both pedestrian jaywalking behavior (gap acceptance and speeds) and the corresponding driver reactions (yielding behavior) for modeling the vehicle–pedestrian interactions (VPI) outside the crosswalks in a micro-simulation environment. The study also quantifies the differences between vehicle–jaywalker and vehicle-permissible crossing. An observational study and an instrumented vehicle study were conducted on the campus of the University of Florida to collect data from pedestrian and driver perspectives, respectively.Crossing speed, yield acceptance and delay of jaywalking crossings and permissible crossings were observed in the study and these attributed can be used for replicating pedestrian operations in simulators. Moreover, behaviors of driver approaching jaywalkers versus pedestrians crossing at designated crosswalks were compared on the basis of yield rates, and vehicle speed profiles. Vehicle yield dynamics were analyzed to model the driver reactions towards jaywalkers. Lastly, it was found that the locations of jaywalking events are highly concentrated and influenced by the crossing environment, such as pedestrian and vehicular volume, bus stops presence and crossing distance.This paper establishes several quantitative relationships describing interactions between pedestrians crossing outside of crosswalks and approaching drivers, which provide the basis and assumptions for modeling such interactions in a micro-simulation environment for traffic operational analyses.

Portuguese two-lane highways: modelling crash frequencies for different temporal and spatial aggregation of crash data

The identification of contributory factors to crash frequencies observed in different highway facilities can aid transportation and traffic management agencies to improve road traffic safety. In spite of the strategic importance of the national Portuguese road network, there are no recent studies concerned with either the identification of contributory factors to road crashes or Crash Prediction Models (CPMs) for this type of roadway. This study presents an initial contribution to this problem by focusing on the national roads NR-14, NR-101 and NR-206, which are located in Northern region of Portugal. They are two-lane single carriageway rural roads. This study analysed the crash frequencies, Average Annual Daily Traffic (AADT) and geometric characteristics of 88 two-lane road segments. The selected segments were 200-m-long and did not cross through urbanized areas. The fixed length of 200 meters corresponds to the road length used in Portugal to define a critical point. Data regarding the annual crash frequency and the AADT were available from 1999 to 2010. Due to the high number of zero-crash records in the initial database, the data were explored to identify the best statistical modelling approach to be adopted. The Generalized Estimating Equations (GEE) procedure was applied to 10 distinctive databases formed by grouping the original data in time and space. The results show that the different observations within each road segment present an exchangeable correlation structure type. This paper also analyses the impact of the sample size on the model’s capability of identifying the contributing factors to crash frequencies. The major contributing factors identified for the two-lane highways studied were the traffic volume (expressed in AADT), lane width, vertical sinuosity, and Density of Access Points (DAP). Acceptable CPM was identified for the highways considered, which estimated the total number of crashes for 400-m-long segments for a cumulative period of two years.

Efficiency of a highway use reservation system for morning commute

This paper examines the design and efficiency of a highway use reservation system where commuters need reservations to access a highway facility at specific times. We show that, by accommodating reservation requests to the level that the highway capacity allows, traffic congestion can be relieved. Generally, a more differentiated design of the reservation system yields a higher reduction of travel cost and thus achieves a higher efficiency. The efficiency bound of the system is established. We also show that braking or tactical waiting behaviors of drivers would cause a loss of efficiency, which thus need be proactively accommodated. Given that user heterogeneity cause further loss of efficiency, we explore how two specific types of user heterogeneity affect the system efficiency. Auction-based reservation is then proposed to mitigate the efficiency loss.