Headway Characteristics Research Articles

Analysis of Time Headway Characteristics at the Curbside Bus Stop on Multi-Lane Divided Urban Arterials under Mixed Traffic Conditions

Analysis of Time Headway Characteristics at the Curbside Bus Stop on Multi-Lane Divided Urban Arterials under Mixed Traffic Conditions

Capacity drop at the bus stop on multilane divided urban roads under mixed traffic conditions

Time headway characteristics are of great importance for planning and design of roadway. The present study determines time headway distribution pattern of vehicular stream at various urban roads and evaluate drop in capacity of roadway section having curb-side bus stops. Field data for present study was collected at 8 different locations on four-lane and six-lane divided sections in the cities of Warangal and Hyderabad in India. The mean time headway of heterogeneous vehicles fitted to various headway distributions for estimating capacity of road section. The factors affecting the capacity have been identified as bus frequency, dwell time, and the average roadway width lost. Percentage reduction in capacity (PRC) is determined to develop regression model. Further, speed-flow diagrams were developed using field observed traffic flow data for determining parameters free-speed, critical speed, and roadway capacity on selected section. After comparing capacity values obtained from two methods, the study determined avg. time headway of vehicular stream under the traffic flow at capacity and free flow conditions. The study also finds capacity value of bus stop section using methodology provided in Indo-HCM (2017). The PRC values estimated based on Indo-HCM guidelines are found to be significantly higher than those estimated by the proposed PRC model. It is due to the Indo-HCM guideline considering only one parameter i.e. bus frequency. The study finds, in addition to bus frequency the dwell time, roadway width lost, and presence of an extra lane also influences the drop in capacity of bus stop section on multilane divided urban roads.

Queue-Based Headway Distribution Models at Signal Controlled Intersection under Mixed Traffic

Headway of vehicles during platoon dispersion at signalized intersection is one of the critical microscopic traffic characteristics in traffic flow theory. The distribution of the discharge headways of vehicles also has a significant impact on the traffic generation process in most of the microsimulation approaches. However, few studies have investigated the vehicle discharge headway for interrupted flow at signalized intersections under mixed traffic conditions. The present study uses data collected from 20 intersections in six cities for comprehensive analysis of discharge headway. A box-and-whiskers plot is generated for discharge headway to quantify its reasonable profile. The diagram shows that headway of vehicles decreases with the queue dispersion. A stable headway can be observed after the fifth vehicle position of a queue, giving a saturation headway of 2.05 s per vehicle. Six types of continuous distribution are tested to model the discharge headway distribution. A statistical investigation is also performed to verify the best-fitted model for each vehicle position in a queue. The ranking of a best-fitted distribution is done for each vehicle position as per the statistical significance. This study demonstrates the discharge headway characteristics and distribution at each vehicle position, which can be useful for traffic flow analysis and especially for improving microsimulation models.

Discharge Characteristics Analysis of Queued-up Vehicles at Signal-Controlled Intersections Under Heterogeneous Traffic Conditions

Characteristics of discharge vehicle play a significant role in the concept of capacity estimation and designing of a signal-controlled intersection. Highway Capacity Manual (HCM) (Transportation Research Board of the National Academics, 5th edn, Washington, DC, 2000) presents a methodology for analysing signalized intersection considering details of each parameter for a lane-based car-dominated traffic stream, with limited applicability for the mixed traffic conditions. The present study analyses the departure headway characteristics of queued vehicles where a decreasing trend is observed with increase in vehicle position with a saturation headway of 2.05 s/veh. The distributions of departure headways are also analysed, and hypothesis result shows that the departure headways at each vehicle position follow a particular log-normal distribution with varying mean and variance. An optimization technique is framed to find out the discharge of vehicles through minimizing the difference between observed flow and ideal flow proposed by HCM (2000). Dynamic passenger car units (PCU) are also estimated through minimizing the Theil’s coefficient for accurate estimation of discharge pattern for mixed traffic conditions. The result shows that optimized discharge pattern is close to the ideal one with maximum saturation flow of 1908 PCUs/h (HCM proposed 1900 PCUs/h). A comparative analysis is done between the obtained flow value and flow value proposed by several guidelines and studies to check its suitability for mixed traffic stream.

Safety and Headway Characteristics in Highway Work Zones with Automated Speed Enforcement

This paper investigated the headway distribution of platooning vehicles in work zones with and without automated Speed Photo Enforcement (SPE). Data from two work zones were collected and analyzed. The portion of vehicles traveling with a very short headway (less than 0.7 sec) was also examined. In addition, the behavior of vehicles near the law enforcement vehicles was analyzed in terms of applying brakes and changing lane in one of the work zones. The results indicated that the mean headway of cars in the median lane significantly increased in both work zones when the SPE van was present compared to the base condition. For trucks, the mean headway increase was significant only in the shoulder lane when the SPE was present. This is a beneficial effect and indicates that drivers had a longer time to react to the lead vehicles. It was also found that the proportion of cars traveling with a very short headway in the median lane significantly decreased when a SPE van was present at one work zone (I-64). In the shoulder lane, no very short headway was observed when SPE was implemented. The difference in braking behavior was not significant when SPE was compared to police car presence. However, lane changing behavior was significantly different for cars traveling in the median lane and also for trucks traveling in the shoulder lane. The proportion of cars changing lanes was 5 percent with a police car present and increased to 8 percent when the SPE van was present. A significant number of trucks changed lanes from the shoulder to the median when the police car was present to comply with state law.

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.

Evaluating the Time Headway Distributions in Congested Highways

Time headway is a significant traffic flow parameter that affects the capacity and safety of highways and freeways. Time headways are broadly used in different areas of traffic and transport engineering such as capacity analysis, safety studies, car following and lane changing behavior modeling, and level of service evaluation. In this paper, the time headway distribution is investigated for an urban highway at different traffic flow rates during congestion. To analyze the headway characteristics, the time headways to the preceding and following vehicles are analyzed for heavy vehicles and passenger cars. The trajectory data used in this study was provided for a highway section in California: Berkeley Highway, I-80. Appropriate models of headway distribution are selected for heavy vehicles and passenger cars using Chi-Square test. Using the selected models, headway distributions are predicted for each vehicle type at different traffic flow rates. The results confirm existence of different time headway distributions in vicinity of heavy vehicles and passenger cars which is due to the difference in the behavior of drivers in vicinity of heavy vehicles and passenger cars under congestion.

Roundabout Critical Headway Measurement Based on High-Resolution Event-Based Data from Wireless Magnetometers

Critical headway is an important parameter for roundabout design, particularly with regard to analytical modeling approaches. The models that have been developed over the past 30 years were typically based on data obtained from manually reduced video or field observations. This paper reports on the application of wireless magnetometers to collect point presence detection for calculating the rejected critical headways. Data were collected at a single-lane roundabout in Carmel, Indiana. Carmel has had more than 60 roundabouts in operation for several years: it represented a community that was highly experienced with roundabouts. More than 260,000 entering vehicles were observed at one of the single-lane roundabouts over a 2-week period with more than 45,000 rejected headways analyzed. For the roundabout studied, 75% of the rejected headways were found to be less than 3.0 s. The rejected headway values were somewhat lower than the values reported in NCHRP Report 572, perhaps because of the evolving driver familiarity with roundabouts. Although this community had a particularly large number of roundabouts, the rejected headway characteristics observed suggested that as roundabouts became more common throughout the United States, it was appropriate to revisit some of the basic traffic engineering parameters used for analysis, much as the traffic signal community did with saturation flow rate in the 1990s. The techniques presented in this paper could be scaled to several roundabouts with varying geometrics and traffic to diversify the data set necessary to update some of the values developed during the past decade before roundabouts were common in the United States.

Estimation of Saturation Flow Rates at Signalized Intersections

The saturation flow rate is a fundamental parameter to measure the intersection capacity and time the traffic signals. However, it is revealed that traditional methods which are mainly developed using the average value of observed queue discharge headways to estimate the saturation headway might lead to underestimate saturation flow rate. The goal of this paper is to study the stochastic nature of queue discharge headways and to develop a more accurate estimate method for saturation headway and saturation flow rate. Based on the surveyed data, the characteristics of queue discharge headways and the estimation method of saturated flow rate are studied. It is found that the average value of queue discharge headways is greater than the median value and that the skewness of the headways is positive. Normal distribution tests were conducted before and after a log transformation of the headways. The goodness‐of‐fit test showed that for some surveyed sites, the queue discharge headways can be fitted by the normal distribution and for other surveyed sites, the headways can be fitted by lognormal distribution. According to the queue discharge headway characteristics, the median value of queue discharge headways is suggested to estimate the saturation headway and a new method of estimation saturation flow rates is developed.

Computer simulation model for the prediction of traffic noise levels

This paper describes a computer simulation model capable of predicting the noise levels generated by traffic passing through road intersections controlled by roundabouts where departures from free-flow traffic conditions occur. The model depends for its operation on the acoustical and flow characteristics of single vehicles travelling on a road from which the overall noise generated by traffic streams can be deduced using a sampling/integration technique. Distance effects, ground cover, vehicle type, velocity and headway characteristics, etc. are taken into account in the model and the simplest possible input parameters are used deliberately to facilitate the eventual use of the model by highway and planning authorities. Good agreement has been achieved between measured and predicted L 10 values for freely flowing traffic negotiating roundabouts. Further applications of the model involving road intersections controlled by traffic lights and the effect of traffic queues are nearing completion.

Characteristics of Traffic Flow on Freeways

Traffic flow characteristics were studied on two high density controlled access facilities in Detroit, Mich; average speeds and volumes were recorded on per minute, per lane basis; paper presents traffic volume characteristics, speed characteristics, vehicle headway characteristics, and relationships of fundamental characteristics; it is concluded that traffic volume affects lane usage and that distribution of traffic volume between lanes follows definite pattern.