Percent Time Spent Following Research Articles

Platoon-Based Assessment of Two-Way Two-Lane Roads Performance Measure: A Classification Method

Two-way two-lane roads have a significant impact on road transportation infrastructure. Platoon formation on two-lane roads is one of the factors that affect the quality of traffic flow on two-lane roads. More specifically, the creation of a platoon increases the density of vehicles and the number of overtaking maneuvers and decreases the traffic performance of two-lane roads. The present study made an effort to investigate the effect of the platoon characteristics on the traffic flow of vehicles on two-lane roads. Moreover, it strived to develop the nonlinear regression model with a new approach to capacity calculation. Finally, a method for estimating the level of service (LOS) based on the number of followers per capacity (NFPC) and LOS classification using the KNN method was presented. Considering these aims, first, the relevant variables (which were related to platoon) including time headway (Ht), average travel speed (ATS), platoon size (PS), average platoon speed (APS), percentage of heavy vehicles (HV), percent time spent following (PTSF), number of overtaking (NO), density (ρ), and traffic flow were investigated on the examined roads. The results showed that the speed and the Ht were the most effective and the least effective platoon characteristics, respectively. Moreover, it was accompanied by the increase in PTSF which resulted in the increase in overtaking maneuver. Finally, the results regarding the developed model showed that the NFPC measure was able to predict the traffic flow of two-lane roads in a more satisfactory way compared to the two criteria, namely, PTSF and ATS in the Highway Capacity Manual (2016) since it increased ATS by 65% and decreased the capacity of two-lane roads by 21%.

Traffic Performance Measures on Two-Way Two-Lane Rural Highways

The most appropriate service measure for a two-lane highway is the combination of average travel speed (ATS) and percent time spent following (PTSF). The local driver behavior and traffic operation characteristics in different countries affect the operational analysis results. The objective of this study is to evaluate the applicability of the HCM procedures on two-lane highways in Iraq. Ten highway segments in northern Iraq were selected, and more than 28,000 vehicles were observed to record traffic characteristics.
 The results show that for low flow rates, the HCM-2000 procedures tend to overestimate the ATS with an amount of 0.0085VP, while for moderate-to-high flow rates, the HCM procedures tend to underestimate the ATS with an amount of 0.0025VP for the highways considered. Moreover, the HCM procedures tend to overestimate PTSF; as well, ATS decreases as PTSF, density, and follower density increase for the highways under study. Equations are developed for the evaluation of traffic performance on two-lane highways in Iraq.

A multi-state merging based analytical model for an operation design domain of autonomous vehicles in work zones on two-lane highways

As a special application of connected and automated vehicles (CAVs), the Autonomous Truck Mounted Attenuator (ATMA) vehicle system is promoted to reduce fatalities in work zone locations. In this manuscript, we focus on the Operational Design Domain (ODD) problem of two-lane highways, i.e., under what traffic conditions should an ATMA be deployed. Due to the dramatic speed difference between ATMA vehicles and general vehicles, a queue will be formed, leading to a percent-time-spent-following (PTSF) increase during maintenance. General vehicles in the queue will assess a gap on the opposite lane to perform a passing maneuver, which is broken down into multi-stage merging behavior. As such, an analytical model is first made, based on queuing theory in which the arrival rate and service rate are analyzed to estimate the PTSF. In this way, the linkage between annual average daily traffic (AADT) and level of service (LOS) is analytically established. Then, the proposed model is validated by comparing the estimated PTSF with that of the Highway Capacity Manual (HCM) values. The comparison results show that the mean error is 9.58%, and the mean absolute error is 12.36%, which demonstrate that the developed model is able to generate satisfactory results when compared with the HCM model. Numeric analysis also shows that roadway performance is sensitive to the K factor and D factor, as well as the operating speed of an ATMA. If LOS = C is a desirable design objective, a good AADT threshold to use would be around 11,000 vehicles per day.

Developing Level-of-Service Criteria for Two-Lane Rural Roads with Grades under Mixed Traffic Conditions

Traffic operations on two-lane rural roads differ substantially from those on divided carriageways due to vehicular interactions between traffic flows in the opposite directions. With the presence of grades and mixed (heterogeneous) traffic, traffic operations on two-lane highways become even more complex and challenging. The present study developed level-of-service (LOS) criteria for assessing the performance of two-lane rural roads with grades. Eight two-lane undivided study sections with grades varying from 1% to 8% were selected. The suitability of well-established performance measures such as percent time spent following (PTSF), number of followers per capacity (NFPC), follower density (FD), average travel speed (ATS), and percent of free-flow speed (PFFS) was evaluated. The results showed that the foregoing performance measures were not practically applicable for characterizing the operational LOS for two-lane rural roads with grades. A new performance measure termed density ratio (DR) was developed in the present study. The ATS, PFFS, and FD measures for different grades revealed no significant difference when visualized at similar DR ranges. Therefore, DR can be considered an effective measure for developing LOS criteria for such roads. The criteria were first developed using DR, ATS, and FD; subsequently, a design LOS was derived.

Development of Direct Models for Percent Time-Spent Following on Two-Lane Highways

The percent time-spent following (PTSF) is a key measure for estimating the level-of-service for two-lane highways. However, PTSF is currently estimated indirectly using various measured field data. This study proposes two alternative direct models for estimating PTSF: (1) a general linear regression model using typically-used input variables and (2) a nonlinear form using only the follower density. Both models are based on data generated from the corridor micro-simulation (CORSIM) software. Comparison of the proposed models with the new directional PTSF analytical model of the Highway Capacity Manual shows that the proposed models are capable of predicting simulation-generated PTSF quite closely with absolute mean error less than 3% using two different sets of validation datasets. The results of this research would be useful for a convenient and direct estimation of directional PTSF of two-lane highways.

Operational Evaluation of Climbing Lanes on Steep Grades and Heavy Trucks

Nearly 99% of Colombian roads have two lanes. In order to improve their level of service (LOS), they have been turned into multilane roads through the doubling of existing highways without technical criteria to justify such transformation, and without considering more appropriate alternatives such as auxiliary lanes. Due to Colombia’s mountainous topography and the high weight/power ratio of the vehicles in circulation, research on auxiliary lanes has been carried out to clarify their applicability. However, operational evaluation procedures such as the Highway Capacity Manual (HCM) may not be representative for the infrastructure and vehicles in Colombia.The hypothesis is that the operational benefits of climbing lanes on two-lane roads with Colombian infrastructures and trucks are higher than the HCM estimate. The objective is to carry out an operational evaluation of the effect of auxiliary lanes on traffic in 84.000 scenarios, and to determine threshold values of operational indicators in order to provide guidance for a better design of this kind of infrastructure.The operational analysis was performed on a virtual road with an auxiliary lane with Colombian trucks and a variety of road geometry and traffic features. Traffic operations were simulated with TWOPAS, part of the Interactive Highway Safety Design Model (IHSDM), for which the computational program PEMAT was created. The results demonstrate the benefits of auxiliary lanes on the improvement of Percent Time Spent Following (PTSF) and Average Travel Speed (ATS), and define criteria for geometric design.

PERCENT TIME-SPENT-FOLLOWING MODEL FOR SINGLE CARRIAGEWAY ROAD

Percent time-spent following (PTSF) is an important parameter in determining level-of-service of a single carriageway road but the current performance measure adopted in Malaysia is based on volume over capacity (v/c) ratio. Therefore, this study aims to develop a new PTSF model that is suitable for single carriageway roads in Malaysia. Traffic flow at 32 sites in various states in Malaysia were recorded using CCTV and video camera. Image processing software was used to extract volume, speed and headway data. Surrogate measure which is the percentage of vehicles travelling with headway threshold values of 3.0 and 5.0 seconds were used in estimating PTSF in the field. Initially, the base PTSF (BPTSF) model was developed and subsequently used to develop six different PTSF models using headway threshold values of 3.0 and 5.0 seconds and different variables. Analyses and performance indicators showed that the model developed based on the headway threshold value of 5.0 seconds with the inclusion of percentage of no-passing zone, opposing flow rate and percentage of heavy vehicles is the best model. This model was determined as the best fit as it has the highest score of 15, which is the maximum score based on performance indicator analysis.

Measurement of percent time spent following on two-lane highways: an exploration of spot and space-based methodologies

Percent Time Spent Following (PTSF) is used as a key performance measure for two-lane highways as recommended by the HCM2010. PTSF is the average percent of total travel time that vehicles must travel in platoons behind slower vehicles due to inability to pass. Despite its acceptance as performance indicator, PTSF is difficult to measure directly in the field. It is therefore estimated using a surrogate measure based on the spot percent of vehicles travelling with headways less than three seconds (3 s) at a fixed point. However, the application of the 3 s headways as the sole criterion in the surrogate measure is still contentious. On the basis of definition, PTSF is both spatial and temporal variable whereas its estimation is based on fixed point. It is therefore desirable to develop a spatial measurement approach for PTSF that takes into consideration of travel time. A new method was therefore developed for spatial measurement of PTSF using a test vehicle equipped with a GPS-based speed acquisition and video recording system. This study explores the spot and spatial measurement techniques of PTSF. The indicator was then measured using the two approaches concurrently. Data for the study were sampled from 18 directional segments of two-lane two-way highways in Johor and Pahang States, Malaysia. Subsequently, the estimates from these approaches were compared. On comparing the PTSF values from the spot and space-based approaches, it was discovered the latter approach produced lower values than the former in most instances. A statistical test of difference of means at 95% confidence level indicated that the estimates from the two techniques do not differ significantly. This implies that PTSF from spot measurement do not differ much from those based spatial approach developed in this study. Finding from this effort would at least substantiate the application of the spot-based PTSF measuring technique; an issue that has been debatable. It also serves as a response to the contentious issue, which has not received the desired attention from experts previously.

A mini review on percent time-spent-following (PTSF) as the service measure for two-lane highways

Percent Time Spent Following (PTSF) is used by the Highway Capacity Manual (HCM) as one of the service measures to assess the level-of-service of two-lane highways since the 2000 edition. But, the problem facing to estimate this parameter is that the difficulty to measure it directly in the field. From several studies, it is known that the HCM analytical procedures applied in PTSF estimation produces inconsistent results with the 3 s surrogate measure and most of them are overestimate. This paper presents a review on estimating PTSF on two-lane highways from several studies that adopted HCM procedures.

Operational Considerations of Passing Zones for Two-lane Highways: Spanish Case Study

The U.S. Highway Capacity Manual (HCM 2010) methodology is used in Spain to evaluate traffic operation and quality of service. In two-lane undivided highways, the effect of limiting where drivers could pass slower vehicles, or passing restrictions, is considered through the percentage of no-passing zones. This measure does not account for how passing opportunities are distributed along the road. The objective of this research was to evaluate the effect percentage of no-passing zones and average passing zone length on a two-lane highway and, if significant, incorporate them in the analysis methodology,. The TWOPAS microsimulation program was calibrated and validated to the Spanish conditions. Passing restrictions had little effect on average traffic speed (ATS), with differences lower than 6 km/h between a road segment with no passing restrictions and a road segment with a passing restriction on 100% of its length. Conversely, passing restrictions can increase the percent time spent following (PTSF) up to 30%. Increasing the passing zone length beyond 2,000 m does not improve PTSF. The new models could be used to better estimate traffic operation on Spanish two-lane highways.

Istraživanje postotka vremena provedenog u koloni na dvotračnim izvangradskim cestama

In Bosnia and Herzegovina (B&H), two-lane rural highways make up the largest percentage of road network and accommodate almost complete traffic. Because of this, platoons are often formed and vehicle speeds are reduced. To improve the quality of traffic flow, it is necessary to define the level of service (LOS) for the existing condition and for alternative possibilities of reconstructing critical elements of the road network. According to Highway Capacity Manual 2010 (HCM 2010), for two-lane highways LOS is defined by measures of efficiency: average travel speed (ATS) for road class I and percent time spent following (PTSF) for road classes I and II. HCM assumes very high ATS values for conditions on national roads that are classified as class I according to HCM classification, and the problem is also nonuniformity of highway geometry elements, which further complicates the application of ATS in B&H. Therefore, PTSF was studied in this paper as an appropriate measure for determining the efficiency of two-lane rural highways. Researches carried out in the world show significant differences in PTSF results compared to the HCM calculations. No research on this topic has been conducted in the region and HCM is used in its original form. The above reasons were the main motive to study this topic and develop a model that would be easy to apply in practice. The survey was conducted on main roads with calculation speed of 80 km/h, because they are the most important in the two-lane road network. In this dissertation, calibration and validation of the Vissim 9 simulation software was first made based on conducted field research. The reason for application of the simulation software is that it allows simulation of different traffic conditions that occur in the field but cannot all be covered by surveying, or for testing some new traffic conditions. Based on the simulations of different traffic conditions, a new model for calculation of PTSF on two-lane rural roads (for speed 80 km/h) was obtained. The obtained PTSF calculation model was validated on another section and the obtained results proved the applicability of the model.

Evaluating Measures of Effectiveness for Quality of Service Estimation on Two-Lane Rural Highways

AbstractThe level of service on two-lane rural highways can be estimated using the percent time spent following (PTSF) and average travel speed (ATS). Because PTSF cannot be directly observed in th...

Preferred time headway of drivers on two-lane highways with heterogeneous traffic

This paper presents an investigation on the adequacy of one of the major performance indicators for two-lane highways, the percent-time-spent-following (PTSF) under changing driver’s behavior in choosing headways. Field study was conducted on a two-lane highway in India that exhibits heterogeneity in its traffic composition and a wide range of flow levels was covered while collecting data. The appropriate headway distributions were selected based on goodness-of-fit test. Exponential or Erlang distributions exhibit their aptness in describing headways up to a volume to capacity ratio of 0.3 and gamma and exponential distributions were compatible for headway data corresponding to a volume to capacity ratio of 0.4 and above. Around 40% drivers were observed to adopt headways 2 s or less at heavy flow when a car-following situation prevails; these headways are considered unsafe in several instances. Further, speed–headway relationships were established to assess a headway threshold beyond which vehicles could be considered free. Empirical investigation indicates a value of about 6 s under such traffic unlike 3 s as considered in PTSF estimation. Another major implication on PTSF is a few drivers move in a platoon by choice even if they have a gap of more than 6 s and passing opportunities.

Evaluation of Models to Estimate Percent Time Spent Following on Two-Lane Highways

AbstractFour analytical models to estimate percent time spent following (PTSF) on two-lane highways were tested with data from 16 sites in Brazil. Besides percent following, the models are based on...

Avaliação de medidas de desempenho para rodovias de pista simples obtidas a partir de relações fluxo-velocidade

Para estimar o nível de serviço em rodovias de pista simples, o Highway Capacity Manual 2010 (HCM2010) adota como medidas de desempenho a porcentagem de tempo viajando em pelotões (PTSF) e a velocidade média de percurso (ATS). A PTSF, no entanto, é praticamente impossível de ser observada em campo. Na literatura, algumas pesquisas propõem medidas de desempenho alternativas à PTSF que podem ser coletadas diretamente da observação do tráfego. Além disso, as relações fluxo-velocidade têm um papel fundamental na determinação do nível de serviço no HCM2010 e no HBS2001. A meta deste trabalho foi avaliar medidas de desempenho provenientes de relações fluxo-velocidade que pudessem ser adequa-das para descrever a qualidade de serviço em rodovias de pista simples no Brasil. Usando dados de tráfego sintéticos produ-zidos com uma versão do CORSIM calibrada para rodovias no Brasil, foram obtidas relações fluxo-velocidade para diferentes condições (geometria, porcentagens de veículos pesados e velocidades de fluxo livre). Comparações dos valores provenientes desses modelos com dados de campo indicaram que a velocidade média de percurso dos automóveis e a densidade para automóveis poderiam substituir os critérios atuais do HCM para estimar o nível de serviço em rodovias de pista simples no Brasil.

Climbing Lane Level of Service Estimation in Spain

A road in Spain was monitored with cameras with the objective of calibrating the TWOPAS model, which was successfully achieved with the information gathered. The model was also applied for estimating its Level of service, with and without a climbing lane, and for comparing the results with those obtained with the Highway Capacity Manual (HCM) procedure.The basic indicators were Percent Time Spent Following (PTSF) and Average Travel Speed (ATS).As a result, it is concluded that the two procedures show improvements on the climbing lane applicable on the field. However, changes are recommended to improve the estimation

Measuring Driver’s Percent-Time-Spent-Following Using a Moving Video Recording Technique

The percent time spent following (PTSF) or proportion of following time (PFT) relative to total travel time taken by vehicles to traverse a particular segment of two-lane highways has been used as key performance index for evaluating the level-of-service of the road. From the context of travel time, this implies that PTSF is a space related indicator and thus supposed to be measured over a road segment. However, this indicator is measured in the field based on specific point observation; as equivalent to the percent of vehicles traveling with time headways shorter than 3 s. The accuracy of PTSF estimates based on this approach has been questioned and criticized by many; as spot measured values may not to be real representative of segment estimates. This paper presents an exploration into the application of moving video recording technique for PTSF measurement. PTSF was estimated based on test vehicle following time on two-lane highways using moving car observer method as an alternative approach for field measurement of the indicator along road segment as opposed the existing practice of spot measurement and assumed representative of long segment. Findings from this work demonstrate that the approach used in this study is promising for field measurement of PTSF; as estimates obtained relate well with the major vehicle’s following cause factors.

Review of Percent Time Spent Following (PTSF) as Performance Measure for Two-lane Highways

The Highway Capacity Manual (HCM) uses Percent Time Spent Following (PTSF) as key service measure for assessing the level of service of two-lane highways. However, the indicator is difficult to measure directly in the field. For this reason, its estimation to date has been based on analytical procedures using equations derived from simulations and field observations at representative location based on surrogate measure; as the percent of vehicles traveling with headway less than 3 seconds (3 s). Findings from empirical studies confirmed that the HCM analytical procedures used in estimating PTSF yield results that are inconsistent with the 3 s surrogate measure and mostly overestimate the indicator. This paper presents a review on the estimation of PTSF on two-lane highways and suggests probable approach to substantiate the application of the current practice. Further, the authors of this paper argued that the use of 3 s as surrogate for estimating PTSF based on field observation at a specific point may not represent the actual time spent following over a long segment of two-lane highway since PTSF is space related measure. Hence, the authors suggest the use of test vehicle approach over the highway segment to be evaluated to identify the variables that are required for the development of a representative PTSF measurement model. It is expected that this review and suggestion offered will contribute in advancing performance analysis of two-lane highways.

Models for Estimating Drivers following on Two-Lane Rural Highways

Traffic performance on two-lane rural highways is commonly characterized by percent time spent following (PTSF), a parameter that determines the level of service on a road segment. Although PTSF is frequently used by transportation engineers and researchers, there is no agreement about its estimation method and values. Therefore, a study was done to calibrate and compare models of PTSF with the data collected on 25 segments of 15 two-lane highways in Israel. The study showed large differences between the collected models and previous model values. Furthermore, the study estimated traffic intensity, which was an additional characteristic of the driver-following phenomenon; this variable did not approach its expected value of 1.0. This lack of agreement between actual and expected values may result from changing driver behavior, that is, impatience as platoon lengths and delays increase. To avoid long platoons, drivers prefer to travel between them and then to perform a passing maneuver sooner than expected. This phenomenon not only reduces platoon length and delays, but also increases the risk of serious and fatal crashes.

Estimating percent-time-spent-following on two-lane rural highways

This study concentrated on estimating the percent-time-spent-following (PTSF) on two-lane highways. This measure is a key estimate of level-of-service in traffic engineering applications. Its evaluation to date has been based on simulations that yielded over-estimated values. The present study shows how to estimate this variable from easily obtained field data based on queuing theory. The estimates accord with opinions on yielding significantly lower values of PTSF that are expressed in the relevant traffic literature. An improved relationship between PTSF and two-way flow is provided by fitting the new estimates by means of the least-squares method.