Highway Capacity Analysis Research Articles

Developing Highway Capacity Manual Capacity Adjustment Factors for Connected and Automated Traffic at Two-Way Stop-Controlled Intersections

Connected and automated vehicles (CAVs) hold great promise in enhancing transportation operations and roadway capacity. However, there is still limited guidance in the field of highway capacity analysis to help agencies account for the potential benefits. This paper investigates the impact of CAVs on the capacity of two-way-stop-controlled (TWSC) intersections and quantifies capacity adjustments under different CAV scenarios. An isolated TWSC intersection is considered in this research to analyze the CAV impacts on various intersection movement capacities under different CAV market penetration rates (MPRs) and conflict flow rates (CFRs). To model CAVs, cooperative adaptive cruise control (CACC) is considered because it directly impacts the vehicle’s longitudinal car-following behavior and therefore the capacity. Additionally, enhanced gap-acceptance behavior based on vehicle-to-vehicle (V2V) communication is included because it can benefit minor road movements via advanced notifications. This paper collects data from customized, well-calibrated TWSC simulation models constructed in commercially available software. The results show that with the increase in MPRs, CAVs can substantially enhance the capacity of the stop or yield controlled movements, and the improvement is more significant under low CFR scenarios. CAVs can also reduce the follow-up headway and thus improve the potential capacity based on the existing HCM TWSC capacity estimation method. Finally, based on the data collected from the simulation, a capacity adjustment factor (CAF) table is proposed for HCM implementation.

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.

ANALYSIS OF IMPROVEMENT ROAD PALIMANAN – KRAMAT SECTION CIREBON REGENCY

Cirebon Regency has a good potential of both in trading and service. So, the roads should contribute to support the driving to comfort for road users . Palimanan – Kramat road is one of the access roads to RegencyCirebon. Along the way Palimanan - Kramat majority to be a place of business. Along Palimanan– Kramat road is a lot of structural damage such as potholes, cracked lengthwise and there is also almost the entire surface of the asphalt peeling. All this happened was possible because the line was often traversed by vehicles such as dump trucks which overload. The purpose of this study is to solve the damage to the road by means of the overlay. The method which is used in this study is a survey method in the location of the Overlay Palimanan – Kramat Road. Analysis of the data which is used are the Summary of Traffic Volume, Volume Peak Hour Traffic, Highway Capacity Analysis, Traffic Growth, Calculation of Pavement Thickness. The results of the study explained that the capacity of the vehicle on roads this time is at 1450 pcu/h, the degree of saturation of 0.3 into the current level of service B that is stable, high capacity most vehicles via this road for 378 pcu/hour. From these results, the road quite smoothly enough so that it can be concluded that the vehicles passing dominated by heavy vehicles with a load of overload which caused damage to the road and the re-layer thickness of 11 cm. Therefore, to note the level of vehicle load so as not to overload the structure of the pavement. Keywords: Road Pavement, Capacity of Road, Road Pavement Structure, Capacity of Vehicles

Applying Problem-Oriented and Project-Based Learning in a Transportation Engineering Course

AbstractA growing consensus in the literature on how to improve the quality of learning suggests that adaptions to problem-based learning (PBL) methods could firstly improve learning experiences, problem solving, skill acquisition and a reasonable level of skill transfer from a student perspective, and secondly develop better professional competence and preparation in these needed highway capacity analysis skills. This paper describes the educational basis of problem-oriented and project-based learning (POPBL) approaches that have been developed as an integral part of a four-year undergraduate engineering degree program at the University of Delaware and incorporated into the transportation curriculum, using real world cases to teach students how to think like expert practitioners. A seven-phase POPBL conceptual framework and the experiences of employing POPBL are presented to demonstrate how it operates in transportation engineering education.

Highway Alignment Parameters Design and Capacity Analysis on Two-Lane Highway

A two-lane highway is an undivided highway with only one lane of traffic in each direction. Two-lane highways are one of the most common roadways at mountainous areas in China. Due to the wider range to choose the horizontal and vertical curves in the design of two-lane highways, the combination of both leads to larger differences on two-lane highway capacities. Thus, the highway alignments are one of the key factors which affect the two-lane highway capacities. According to the empirical data and existing studies, it is regarded that there is no impacts on the capacity for horizontal curves with a radius more than 400m and vertical curves with the gradient less than 3%. Two concepts are defined as effective bending and effective gradient which represent the extent the horizontal curve bends and the steepness of vertical curve respectively. The method to calculate effective bending of horizontal curve and steepness of vertical curve is given and its relevant properties are also discussed. According to the simulation results and the principle of speed differences, the effective bending and effective gradient have been classified into 7 and 6 levels, separately. As a result, there will be 42 combinations of different highway alignments of two-lane highways based on the different combinations of the effective bending and effective gradient. Under this circumstance, the relationship of speed-volume and volume-PTSF (percent time spend following) are obtained from the simulation results. Finally, the capacity of two-lane highway is given under different highway alignments of two-lane highway at mountainous areas in China.

Implementing Auxiliary through Lanes in Context of Highway Capacity Analysis

Auxiliary through lanes (ATLs) are often implemented at congested signalized intersections where fiscal and right-of-way constraints do not allow for full roadway widening. Previous research has suggested that ATLs are used significantly less than the theoretical capacity of a continuous lane. However, analysts have had little empirical basis for evaluating ATL operations in the context of the 2010 Highway Capacity Manual (HCM). Two empirical models that predict the flow in the ATL as a function of congestion and total through-movement flow are presented. A method is described for incorporating the model's findings into the HCM procedure for estimating approach capacity. The study addresses the challenges of modifying the HCM lane utilization factor and accounting for the iterative effect of actuated signal control on ATL use. The study suggests that a cyclic process can be used to balance the ATL flow with the green-to-cycle-length ratio. A method is presented for determining the upstream ATL length needed for efficient ATL operations. Two example problems illustrate the use of the new models in the context of HCM 2010.

Estimation of Passenger Car Equivalents Based on Capacity Variability

Passenger car equivalents are used in highway capacity analysis procedures to convert mixed traffic stream volumes into equivalent passenger car volumes. This paper presents a new empirical method for estimating passenger car equivalents for heavy vehicles on freeways. The proposed approach is based on the concept of stochastic capacities. Capacity distribution functions are estimated in passenger car units. With a determination of the equivalency factor for which the coefficient of variation of the capacity distribution function becomes minimal, passenger car equivalents for heavy vehicles can be derived. The methodology is demonstrated for a number of freeway bottlenecks. The new approach also gives insight into the extent at which the variance of prebreakdown volumes is attributable to variable percentages of heavy vehicles.

Effect of Weigh-in-Motion System Measurement Errors on Load-Pavement Impact Estimation

Weigh-in-motion (WIM) technology has found increasing application in the highway and transportation areas for traffic data collection for the purpose of highway capacity analysis, aiding enforcement and, most recently, pavement design. The measurement accuracy of a WIM scale is critical. There are numerous existing studies involving the measurement accuracy per se; however, the implications and effect of the accuracy in the context of pavement design have been rarely examined. To address this issue, two particular aspects are considered in this study. First, with traffic data obtained from WIM stations in Texas, axle load spectra are developed from both statistical data fit and load-pavement impact perspectives. Axle load spectra are shown to be captured best by mixed-lognormal distributions. Second, based on the first aspect, two scenarios are investigated by incorporating two types of errors into the load measurements: (1) A random error component due to the WIM scale intrinsic properties; and (2) a systematic error component due to the improper calibration of WIM system. The relationship between jointly varying measurement error levels and load-pavement impact estimation errors is established. It is demonstrated (and quantified) that both types of errors contribute to load-pavement impact estimation inaccuracy. The random error leads to overestimation of load-pavement impact. The results also show that WIM system calibration is of more importance because load-pavement impact estimation is more sensitive and significantly related to systematic error than random error. In addition, the estimated load-pavement impact is found to be more sensitive to overcalibration (positive bias) than undercalibration (negative bias) condition. In summary, the findings in this study provide an effective and efficient approach to evaluate WIM measurement errors in conjunction with load-pavement impact in pavement design and rehabilitation. The findings in this study could be further applied for the determination of adequate pavement design reliability standards. Results can also be useful to highway agencies in assessing and selecting WIM equipment.

Implementing the Concept of Reliability for Highway Capacity Analysis

A stochastic concept for highway capacity analysis is presented. The capacity of a highway facility is regarded as a random variable instead of a constant value. Thus, the stochastic approach provides new measures of traffic flow performance based on aspects of traffic reliability. A method for the estimation of capacity distribution functions from empirical data based on statistical methods for lifetime data analysis is introduced. This method is derived for the analysis of freeway capacity. However, the stochastic approach also is shown to be applicable to intersections. Results of the analysis of data samples from freeway sections in Germany indicate that freeway capacity is Weibull-distributed with a considerable variance. A Monte Carlo technique based on the stochastic description of capacity is proposed to quantify freeway traffic performance over a whole year. This technique also provides a quantitative assessment for oversaturated conditions.

Space Standards for Sizing Air-Terminal Check-in Areas

The appropriateness of the current space standards (occupancy rates) for airline check-in area design is discussed. Based on a study of passenger walking patterns at the two international airports in Montreal, it is suggested that the design standards recommended in the International Air Transport Association guidelines result in an oversupply of space, sometimes in excess of twice the required minimum. This is attributed partly to the definition of capacity and the lack of a formal procedure for treating items such as luggage, carts, and stationary passengers that impede movement. It is proposed that the design occupancy rate be determined by adjusting the maximum occupancy rate to account for the impedance. Maximum occupancy rate is derived according to the relationship between occupancy rate and walking speed of passengers without baggage or carts, whereas adjustment factors are computed along the same principles as the passenger-car equivalency factors used in highway capacity analysis. The standard equivalent passenger in the present case is defined as a stationary passenger without a cart, and the space required by moving passengers with and without carts is estimated relative to the standard passenger. Application of the technique is explained using a numerical example.

Travel Impact Evaluation for Major Highway Reconstruction Projects

A key issue in planning major highway reconstruction projects is the allocation of roadway space between the reconstruction activities and the motorists. Estimates of the travel impacts of alternative allocations are required to determine the appropriate use of roadway space. A review of available analysis tools and of experiences with traffic management during reconstruction led to the development of the travel impact evaluation process and the guidelines for selecting appropriate analysis tools presented herein. In summary, the magnitude of the capacity reduction (relative to traffic demand) on the highway being reconstructed determines the appropriate scope of the evaluation. If the capacity reductions are minor, then traffic is unlikely to divert from the reconstruction zone and the evaluation may be limited to the highway being reconstructed, in which case the evaluation could be performed using highway capacity analysis procedures or traffic simulation models. If capacity reductions are significant, then motorists are likely to change their travel patterns and the evaluation should be corridor‐wide, in which case an analysis tool with traffic assignment capabilities must be used.

Driver Population Factor in New Highway Capacity Manual

The 1985 Highway Capacity Manual suggests the use of an adjustment factor called fp to reflect the influence of driver population on the highway capacity analysis for freeways and multilane highways. The manual recommends a value of fp equal to 1.0 for commuter traffic streams or other regular users of a facility and a range of fp between 0.75 and 0.90 for ``other'' types of traffic streams. As a prerequisite to an appropriate application of the factor fp, a systematic and objective method that can be used for classification of highways according to driver population characteristics is described. Using data from two Canadian provinces, seven classes of roads are identified on the basis of trip purpose and trip length distribution. Suggested values of fp are listed that can be used as a ``guide'' in exercising an engineering judgment in selecting a specific fp value for a particular type of traffic stream.

The driver population factor and its influence on highway cost–volume curves

The Highway Capacity Manual is a publication widely used throughout the world as a guide to highway capacity and level of service analysis. The third and the latest edition of the Manual, a 1985 publication of the United States Transportation Research Board, has introduced, among many other changes, an adjustment factor called fp to reflect the influence of driver population on the highway capacity analysis for freeways and multilane highways. This note reviews and elaborates on the driver population factor. As a prerequisite to an appropriate application of the factor fp, this note refers to a systematic and objective method that can be used for classification of highways according to driver population characteristics. By taking an example of the road classes in Alberta, the note suggests a set of fp values that can be used as a guide to exercise an engineering judgement in selecting a specific fp value for a particular type of traffic stream. Also included in this note is a brief economic analysis carried out with an objective of determining the importance and sensitivity of the factor fp in transportation analysis. Key words: cost–volume curves, driver population factor, economic analysis, highway capacity, road classification, traffic stream characteristics.