Uninterrupted Flow Facilities Research Articles

An overview of speed model study under different types of facilities in Malaysian roadway system

The present paper reviewed past studies related to speed model studies and the measured traffic parameters used by other researchers. The purpose of the paper is to discover the relationships between speeds with the differences in roadway condition & characteristics, traffic composition, driver behaviour and to propose a research gap related to the future study of Malaysian road conditions. Fundamental relationships were observed over different parameters and were found to be significantly different. However, under uninterrupted flow facilities, using free-flow speed as a prediction for highway capacity analysis and determining the level-of-service (LOS), the time headway threshold, and the speed of observations at certain flow rates must be carefully studied to represent the free-flow speed in ideal conditions. The paper review helps the authors find research gaps for an in-depth investigation of the free-flow speed on Malaysian highways or expressways. Hence, the finding from the paper reviewed will be used in a future research study on developing a free-flow speed model based on the basic section of roadway in Malaysia.

Characterizing the impact of production adaptive cruise control on traffic flow: an investigation

ABSTRACTThis research conducted a comprehensive study to better estimate the impact of production Adaptive Cruise Control (ACC) on uninterrupted flow facilities using the highly cited ACC car-following models in the literature. Four different car-following models were investigated, including the Autonomous Adaptive Cruise Control (AACC) model, Intelligent Driver Model (IDM), California Partners for Advanced Transit and Highways (PATH) empirical ACC model, and the Technical University of Delft empirical ACC model. Each of the four models were recalibrated using data collected by a 2013 Cadillac SRX with production ACC engaged while following a human-driven 2013 Cadillac SRX in northern Virginia. Off-the-shelf commercial microscopic simulation software VISSIM was utilized to simulate the ACC traffic flow. Sensitivity analysis was conducted on ACC market penetration and following headway. Capacity and fundamental diagrams were used to quantify the impact of the ACC on traffic flow. Results indicate that freeway capacity highly depends on the market penetration of ACC vehicles. Small number of ACC vehicles (<25%) is beneficial to roadway capacity, while wider deployment of ACC vehicles (>75%) significantly harms capacity. The results strongly suggest the urgent need for vehicle connectivity.

Lane by lane analysis of vehicle time headways — Case study of Izmir ring roads in Turkey

The studies on headway characteristics of traffic flow in Turkey are mainly dealing with signalized arterials, intersection approaches or roundabouts. Only a few studies can be found on headway characteristics of uninterrupted flow facilities and nearly none of them are on lane by lane basis. In this study, the authors are modeling headways of vehicles at zmir ring roads by lane by lane principle. The study demonstrates that lognormal distribution is an effective tool to define headways. In addition, the applicability of Cowan M3 distribution to time headways is investigated. Proportion of free vehicles is modeled for different lanes. The results show that traffic flow in the middle lane is highly affected by the vehicles in other lanes. Vehicles in the outer lane can be assumed to arrive randomly, but they are also disturbed by vehicles in other lanes. These results can be used in capacity and performance analysis of freeway segments, ramp junctions and weaving areas.

Calibration and Evaluation of Link Congestion Functions: Applying Intrinsic Sensitivity of Link Speed as a Practical Consideration to Heterogeneous Facility Types within Urban Network

This paper explores the use of archived data to calibrate volume delay functions (VDFs) and updates their input parameters (capacity and free-flow speed) for planning applications. The sensitivity analysis of speed to change in congestion level is performed to capture functional characteristics of VDFs in modeling specific facility types. Different sensitivity characteristics shown by the VDFs indicate that each function is suitable to a particular facility type. The results of sensitivity analysis are confirmed by the root mean square percent error (RMSPE) values calculated using the Orlando Urban Area Transportation Study (OUATS) model results and observed data. The modified Davidson’s function exhibits remarkable performance in nearly all facility types. The strength of the modified Davidson’s function across a broad range of facilities can be attributed to the flexibility of its tuning parameter, μ. Fitted Bureau of Public Road (BPR) and conical delay functions show lower RMSPE for uninterrupted flow facilities (freeways/expressways, managed lanes) and higher values for toll roads (which might have partial interruptions due to toll booths) and signalized arterials. Akcelik function underperforms on freeways/expressways and managed lanes but shows some improvements for toll roads and superior results for the signalized arterials. This was a desired strength of Akcelik function when modeling link travel speed on facilities where stopped delays were encountered.

Determining Level of Service on Freeways and Multilane Highways with Higher Speeds

The Highway Capacity Manual provides a means for evaluating level of service on freeways, highways, and urban streets. Presently, the Highway Capacity Manual methodology is not able to evaluate level of service on freeways with free-flow speeds greater than 75 mph or multilane highways with free-flow speeds greater than 60 mph, and many states now have facilities with posted speed limits that exceed these free-flow speeds. Recent research, conducted by the Texas A&amp;M Transportation Institute (TTI), developed speed prediction equations for uninterrupted flow facilities with higher posted speed limits. From these equations, this paper develops procedures for calculating free-flow speed on facilities with higher posted speed limits and develops methods for estimating level of service on freeways with free-flow speeds up to 85 mph and multi lane highways with free-flow speeds up to 80 mph. For freeways, the recommendations call for utilizing the TTI speed prediction equations to calculate free-flow speed and using the calculated free-flow speeds to determine level of service from speed–flow curves developed within this paper. For multilane highways, recommendations call for utilizing the TTI speed prediction equations to calculate base free-flow speed, which is part of the equation for calculating free-flow speed, and then using the calculated free-flow speed to determine level of service from speed–flow curves developed within this paper. To aid practitioners, step-by-step procedures are provided for applying the TTI speed prediction equations within the Highway Capacity Manual methodology.

Factors Affecting Driver Speed Choice along Two-Lane Rural Highway Transition Zones

Two-lane rural highways attract trips between traffic generators such as residential villages or small commercial areas and are generally uninterrupted flow facilities that provide a high level of mobility with high posted speeds limits. When passing through developed areas, the posted speed limit may be lowered to encourage reduced vehicle operating speeds. No published guidelines currently exist for the design of transition zones that connect high- to low-speed operating environments on two-lane rural highways. The objective of this research was to collect operating speed and roadway characteristic data along two-lane rural highway transition zones in Pennsylvania to explore the roadway, roadside, and traffic control factors that are associated with driver speed differentials. Single- and multilevel models were estimated and compared. The posted speed limit reduction as well as a change in the paved shoulder width, total number of driveways, various advance warning signs, the transition zone length, and the presence of horizontal curves were shown to increase the expected speed reduction in transition zones in the models. Additionally, drivers entering transition zones at higher speeds were found to have greater speed reductions than drivers entering the transition zone at lower speeds.

Development and calibration of the Anisotropic Mesoscopic Simulation model for uninterrupted flow facilities

This paper presents the development, analysis, and calibration of the Anisotropic Mesoscopic Simulation (AMS) model for uninterrupted flow facilities, such as freeways. The proposed AMS model is a vehicle-based mesoscopic traffic simulation approach that explicitly considers the anisotropic property of traffic flow into the vehicle state update at each simulation step. The advantage of AMS is its ability to address a variety of uninterrupted flow conditions in a relatively simple, unified and computationally efficient manner. The discussions focus on the key modeling concepts, the analytical properties and numerical analysis, and the calibration process and results. The addressed analytical properties are the overtaking conditions, acceleration and deceleration rate bounds, and shockwaves. The numerical analysis includes both freeway segments as well as merging junctions. Considerable efforts were devoted to employ the Next-Generation Simulation (NGSIM) program datasets to calibrate the AMS model parameters. The high traffic fidelity and satisfactory computational efficiency make AMS a promising simulation approach for large-scale regional dynamic traffic simulation and assignment.

Default Values for Highway Capacity and Level-of-Service Analyses

The Highway Capacity Manual (HCM) is the authoritative source providing state-of-the-art methodologies for evaluating highway, transit, bicycle, and pedestrian facilities. Default values are used to represent input parameters when the input parameters are difficult to measure or estimate. A default value is a representative value that may be appropriate for estimating an input parameter in the absence of local data. Before this study was done, no nationwide research effort had been conducted to assemble field measurements to determine whether the default values in the HCM represent typical field conditions. A sensitivity analysis was conducted for the input parameters in HCM 2000 that influence the service measures calculated in the HCM methodologies. Nineteen of these input parameters were determined to have a high degree of sensitivity in influencing the service measure results. These sensitive input parameters influence the service measures for the following HCM chapters: Urban Streets, Signalized Intersections, Pedestrians, Bicycle Paths, Multilane Highways, and Basic Freeway Segments. Based on the assembly of a nationwide database, specific default values were recommended for heavy vehicle percentages and peak-hour factors for uninterrupted flow facilities (freeways, multilane highways, and rural two-lane highways). It is recommended that default values for some input parameters continue to be developed based on existing HCM guidance. Other input parameters should be based on field measurements obtained from design plans. Additional guidance is provided to aid in the selection of default values based on the review of recent research documents.

Evaluation of Performance Measures for Two-Lane Expressways in Japan

Two-lane expressways exist as provisional sections for future expansion to four-lane expressways in Japan, although recently such roadway types have been considered for construction for permanent use. Their highway classification may fall somewhere between common (multilane) expressways and ordinary two-lane highways, with full access control and high speed limits but with only one lane per direction of travel. Since this type of highway is unique, methodologies for service level measurement of other uninterrupted-flow facilities are not applicable. Percent time spent following, for instance, is estimated with significant consideration of the opposing flow rate, which has practically no effect on driving conditions since a median barrier is present in all sections. The goal of this study is to analyze and compare possible performance measures that would best describe the traffic operational characteristics of two-lane expressways. Among the performance measures considered, follower density had much promise, having shown strong relationships with flow rate. Since the available data were only those taken during off-peak periods, further observations of follower flow must be made during congested or near-congested flow to establish follower density and volume relationships for all traffic conditions.

Evaluation of Performance Measures for Two-Lane Expressways in Japan

Two-lane expressways exist as provisional sections for future expansion to four-lane expressways in Japan, although recently such roadway types have been considered for construction for permanent use. Their highway classification may fall somewhere between common (multilane) expressways and ordinary two-lane highways, with full access control and high speed limits but with only one lane per direction of travel. Since this type of highway is unique, methodologies for service level measurement of other uninterrupted-flow facilities are not applicable. Percent time spent following, for instance, is estimated with significant consideration of the opposing flow rate, which has practically no effect on driving conditions since a median barrier is present in all sections. The goal of this study is to analyze and compare possible performance measures that would best describe the traffic operational characteristics of two-lane expressways. Among the performance measures considered, follower density had much promise, having shown strong relationships with flow rate. Since the available data were only those taken during off-peak periods, further observations of follower flow must be made during congested or near-congested flow to establish follower density and volume relationships for all traffic conditions.

Field Measurement of Signalized Intersection Delay for 1997 Update of the Highway Capacity Manual

The 1997 update of the Highway Capacity Manual changes the basis of delay for level-of-service determination at signalized intersections from stopped delay to conceptually more appealing total delay. Total delay is made up of components including volume, control, and geometric delay. Level of service is now defined in terms of control delay, which provides a more stable and tractable relation to total delay, but the issue of field measurement remains in any case. A combined theoretical and empirical approach to measuring field delay on the basis of typical vehicle deceleration and acceleration profiles is taken in this paper. The profiles are related to the relatively easily surveyed quantity of vehicles in queue, which is equivalent to estimating time in queue of all vehicles stopped by the traffic signal. The results indicate that after vehicles in queue are sampled, correction factors can account, in practical terms, for the unsurveyed deceleration and acceleration delay. The corrections are simple additive factors that are a function of free-flow speed and average number of vehicles stopped in queue. Another adjustment is included for the consistent tendency of human observers to overestimate vehicles in queue. All of these factors are included in the new 1997 HCM procedure for measuring signalized intersection delay in the field. Further identified work includes the need to fully develop the total delay concept to account for geometric delay consistently over a variety of interrupted- and uninterrupted-flow facilities. Such resolution should be included in HCM 2000 preparation currently in progress.