Estimation of distance headway on two-lane highways using video recording technique

Distance headway is the physical separation, in meters, between any pair of successive vehicles in a traffic lane measured from same common feature of the subject vehicles; either rear-to-rear or front-to-front. It is a significant microscopic traffic flow characteristics parameter used in various traffic engineering applications such as level of service, highway capacity analysis, traffic safety and microscopic traffic simulation. Its values are also essential in evaluation of congestion level and overtaking manoeuvre related problems. Distance headway, being spatial parameter is difficult to measure directly in the field. However, it is usually estimated from other parameters; particularly, traffic density, which is also difficult to measure directly but estimated from other parameters based on spot observation. Estimates of distance headways from such approaches may not be real representation of desired values, especially for situations where the parameter is to be evaluated at intervals over a roadway segment. This paper presents a novel approach for direct field measurement of distance headway on two-lane highways using video recording instrumented vehicle. Data for the study were collected from six segments of two-lane highways from Johor, Malaysia. Findings form the study demonstrate that the approach reported herein can be used to measure distance headway directly in the field as against the existing practice of estimating it from other variables based on spot observation despite the fact that it is a spatial parameter

Comparison of free flow speed estimation models

Free flow speed (FFS) is the drivers’ desired speed on roadways at low traffic volume and absence of traffic control devices whose determination is a fundamental step in the analysis of two-lane highways. FFS can either be estimated using either analytical model or based on field measurement. Regarding the former approach; the Malaysian Highway Capacity Manual (MHCM) established a model for estimating FFS based on base-free-flow-speed (BFFS), roadway’s geometric features and fraction of motorcycles in the traffic stream. On the other hand, the Highway Capacity Manual (HCM) suggested an approach for field measurement of FFS; preferably at a two-way flow rate not exceeding 200 veh/h. For many highways, observing a two-way flow rate of 200 veh/h or less is seldom met or impossible. In such situations, mean speed could be observed at higher flow rates and adjusted accordingly using a model provided by the HCM. This study describes the application of the two approaches for measuring FFS. Moving car observer (MCO) method was used for collecting the relevant data related to travel time, speed, flow rate, and traffic composition with using a video recording instrumented test vehicle while the roadway geometric features were measured manually. Data for the study were collected on four directional segments of rural two-lane highways with varying geometric features and traffic composition in Johor, Malaysia. Field data obtained were analyzed to estimate the FFS using the two approaches. Results obtained from both methods were compared to ascertain the degree of their consistency or otherwise. Statistical analysis using student t-test indicates that there is no statistically significant difference between the FFS estimates from the two approaches

Empirical evaluation of drivers’ operating speeds along curvatures on single carriageway roads

Choice of vehicle’s speed is one of the most important factors for a driver for proper vehicle’s control and selecting a wrong speed results in loss of vehicle’s control; particularly in negotiating road curvatures. Many of such speed related errors could be attributed to inconsistencies in the road alignment, that surprise the driver as a result of sudden change in road characteristics leading to an excess critical speed, hence, losing the vehicle’s control. This inconsistency should be accounted for and controlled by the engineers. This study was carried out to evaluate the speeds of the drivers when negotiating various layouts of road bends, determination of possible factors affecting drivers’ operating speed and development of prediction models for operational 85th percentile driver’s speed. Speeds of over 4000 vehicles (light and heavy) were collected at 10 road curves of various designs using speed radar meter and video recording system. Speeds were measured at three different points along the curves; the entry, mid and exit points. Preliminary findings from this study revealed that there are some inconsistencies in the features of the existing road curves. The design of the existing curves used in this study can be regarded as fair as the change in the operating speed of light vehicles was found to be higher than 10 km/h; being the established lower limiting value. Likewise, the road curves could also be regarded to fall within a fair and poor design because the average change in operating speed exceeded the limiting value of 20 km/h when compared with the posted speed limit. However, more data would be required to improve the accuracy of the results

Drivers decision model at an onset of amber period at signalised intersections

Driving is a complex task and, probably, the most dangerous activity on roadways because it involves instantaneous decision making by drivers. A traffic signal–controlled intersection is one of road facilities which require drivers to make an instantaneous decision at the onset of amber period. This paper describes the application of a regression approach to evaluate the factors that influence the decision made by a driver whether to proceed or to stop at the stop line at the onset of amber period at signalised intersections. More than 2,700 drivers approaching the stop–line at the onset of amber period at six intersections installed with a fixed–time traffic signal–control system were observed. Two video cameras were used to record the movements of vehicles approaching the intersection from a distance of about 150 metres. The data was abstracted from the video recordings using a computer event recorder program. The parameters considered in the analysis include vehicles’ approaching speed, distance from the stop line at the onset of amber, the position in the platoon as well as the types of vehicles driven. The result of the analysis shows that about 13.43% of the drivers tend to accelerate to clear the intersection at the onset of amber period and about 26.32% of the drivers ended up with running the red light. A binary logistic model to explain the possible decision made by a driver for a given set of conditions was developed. The analysis shows that the probability of drivers’ decision either to stop or proceed at an onset of amber period is influenced by his/her distance from the stop line and his/her position in the platoon

Effect of vehicular traffic volume and composition on carbon emission

Road intersection is one of the causes of air pollution or toxic gases emission because at such location vehicular traffic are either required to slow down or completely stop for them to secure a safe and acceptable gap to perform a particular type of manoeuvre. The level of gaseous emissions usually increases with corresponding increase in traffic. The level of the environmental pollution depends on the type of intersection. This study evaluated the amount of carbon monoxide (CO) emissions from vehicular traffic for both morning and afternoon peak periods at roundabout and priority intersections. Carbon monoxide emissions at the intersections were first measured using GrayWolf Sensing Solution (GWSS) upon which the results obtained were used in calibrating SIDRA software for estimation of CO emission. SIDRA emission estimates were derived from traffic flow parameters; traffic volume, compositions, speeds and turning movements, as well as road geometry. Calibration factors were then derived in order to make SIDRA a reliable means for measurement of vehicle emission. Further, CO emissions traffic models were developed for the two types of intersections evaluated in this work for both morning and afternoon peak periods for two different observations periods (5 minutes and 1 hour traffic volumes) using multiple regression analysis. The models developed described how vehicular traffic volume and compositions affect CO emissions at road intersections. Further analysis revealed that roundabout is a better form of intersection as it reduces the amount of CO emission when compared to simple priority intersectio

Effect of skewed signalised T-intersection on traffic delay

Intersections are places where two or more highways intersect. Their performance dictates the performance of the rest of the traffic network. When two highways cannot intersect at right angles due to some geometric constraints, skewed intersection forms. Generally a traffic signal system is designed to control traffic movements at road intersections without considering the orientation of the intersection. Such an approach might lead to inaccurate assessment of operational performance of a signalised intersection because such a configuration influences turning radius and hence the vehicle’s negotiation speeds. This paper describes the result of a study carried out to evaluate the effect of orientation of a signalised intersection on the control delay to vehicular traffic. The evaluation was carried out using aaSIDRA software, which was calibrated using the data collected from site. Two models of skewed intersection based on a normal T–intersection were simulated at minor approach at 45º (i.e. skewed to the left), and 135º (i.e. skewed to the right), respectively. The result of the analysis showed that delay to the motorists in the minor approach increases when the minor approach is skewed from left to righ