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

Approximation of time headway on two-lane highways using test car approach

Time headway is an essential variable in various traffic engineering applications such as capacity and level of service (LOS) analyses of road segments and intersections, traffic safety analysis, generation of vehicles in microscopic simulations, and so on. From the context of LOS analysis of road segments, the proportion of traffic traveling with headways less than 3 seconds at a point is used as a criterion for assessing the operational performance of two-lane highways. Generally, headways are measured based on spot observation as the time interval between two consecutive vehicles passing a common point of a road. Spot measurement has been identified as the major problem associated with headway data collection as the approach does not consider the variation of the headways along the road segment. It is therefore, essential to develop other techniques for estimating headway along road section as opposed the current practice of spot measurement and deemed applicable for longer segment. This paper presents a new approach for measuring time headway based on space observation using test vehicle method. Field data on time headways were collected on two-lane highways using both spot and space observations and the results compared. Statistical analysis using t-test indicates that the two data sets do not differ significantly

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

Modelling of percent time spent following using spatial measurement approach for two-lane highways

Percent Time Spent Following (PTSF) is used as a key service measure for two-lane two-way highways, as recommended by the U. S. Highway Capacity Manual (U. S. HCM). 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. Hence, it is estimated using a surrogate measure, i.e. based on the percent of vehicles travelling with headways less than 3 s as recommended by the U. S. HCM or use of a model derived from such estimates or a simulation approach. However, the applicability of the 3 s headways as the sole criterion in the surrogate measure is still debatable. By definition, PTSF is a spatial variable, whereas its estimation is based on fixed point, which may not be a representative of a segment‟s performance. Therefore, this approach fails to incorporate the travel time associated with PTSF. Hence, it is desirable to develop a spatial measurement approach for PTSF that takes into account of travel time and to derive a new PTSF model. This could substantiate the application of the 3 s surrogate measure. This study explores the application of test vehicle method for spatial estimation of PTSF and derives a model based on traffic flow and roadway geometric variables. Data for the study were sampled from twenty four (24) directional segments of two-lane two-way highways in Johor and Pahang States, Malaysia. A test vehicle equipped with a GPS-based speed acquisition and video recording system was used for the data sampling. PTSF was estimated as the average percent of total travel time spent by the test vehicle behind slower vehicles at headways less than 3 s. An empirical model to estimate PTSF for ranges of traffic flow and roadway geometric conditions with a reasonable accuracy was developed. A statistical analysis showed that there is no significant difference between PTSF obtained from the model derived in this study and those from the surrogate measure at α = 0.05. This finding supports the application of the surrogate measure based on the U. S. HCM which had been debated for long. It equally serves as a response to the contentious issue, which had not received the desired attention from experts hitherto. However, a comparison between PTSF from this study model and each of the Malaysian Highway Capacity Manual (MHCM) and the U. S. HCM models revealed that both MHCM and U. S. HCM models overestimate PTSF significantly at α = 0.05. This implies that PTSF based on the MHCM and U. S. HCM models would lead to erroneous designation of a road segment‟s level of service, which would in turn suggest for a premature facility improvement with attendant unjustified expenditures

Spatial evaluation of speed-flow-geometry relationship on two-lane rural highways

The mean travel speed of drivers on uninterrupted flow facilities such as two-lane rural highways is deemed as good performance indicator for the subject road class; as the variable relates well with user perception. However, the operating conditions on two-lane roads relating to travel speed is different from those on other types of facilities, as fast moving vehicles in either direction are usually impeded by slower moving ones in the same travel direction and also facing oncoming traffic in the opposing lane. Thus, impeded vehicles may be compelled to travel at lower speeds than desired; particularly, in the absence of sufficient sight distance and permissible gap in the opposing traffic stream, being the appropriate lane used for passing maneuvers. This implies that the operating speed on two-lane highways substantially depends on the level of traffic flow and perhaps, its composition as well as the roadway geometric features. This paper examines the effects of traffic level, composition and road geometric features on the operating speed on two-lane highways based on a spatial approach. An empirical model relating mean travel speed to traffic flow parameters and highway geometric features was derived for prediction of mean travel speed on two-lane rural highways based on easily observable variables

Determination of Appropriate Source-to-Detector Distance Dependence of Gamma Spectrometry System to Achieve Higher Resolution

Operation of gamma spectrometry requires intensive monitoring of gamma ray fluxes. When a radioactive intense source is placed close to a crystal detector, it becomes saturated as a result of detector dead time. On the contrary, when placed far away, there is loss of count statistics. For this reason, optimal position for placing the source has to be investigated. With the improvement in the instrumentation of radiation detection applications over the years, high count rate measurement accuracy is more crucial than ever. This is due to periodic measurement and new correction models for dead time. The aim of this study is to examine the performance of two gamma spectroscopic systems. The source detector distance dependence on dead time, peak-to-compton ratio, overall amplifier gain, FWHM, and voltage variation were investigated using American standard procedures (ANSI/IEE -325). Measurements were performed at five (5) different distances of detector cap for four (4) point sources (Co-60, Eu-152, Cs-137 and Ba-133). Source-to-detector distance at 25 cm was improved to avoid summing coincidence and dead time correction. The results obtained at 25 cm showed that the dead time was found less than 1% as compared to 4 cm. This will describe the stability of dead time. It also indicated that for both detectors the rise in biased voltage will yield a good resolution at 1332.5 KeV. This study is significant as it provides information to ensure that detectors are kept at optimal distance to achieve good dead time

Performance Evaluation for an Optimized Wenner (ALPHA, BETA, AND GAMMA) Arrays Using Synthetic Geological Models

The study aimed at comparing the resolution and effectiveness of three-electrode arrays (Wenner-α, Wenner-β, and Wenner-γ) in the 2D Electrical resistivity method using Numerical analysis of geological models. Three synthetic geological models that simulate block-one dyke and water layer were generated using RES2DMOD software. The inversion used for the geological models was based on smoothness-constrained least-square inversion which was carried out with RES2DINV. The inversion results were imputed into surfer11 software to examine the image resolution, thereafter absolute percentage error (APE) was calculated to measure the effectiveness of the arrays. The result for the block-one model shows that the Wenner-β array has an APE of 14.45%, the Wenner-α array has an APE of 32.67%, and the Wenner-γ array with an APE of 29.15%. Similarly, for the dyke model, the Wenner-α array, Wenner-β array, and Wenner-γ array have an APE of 69.61%, 57.43%, and 45.49% respectively. However, the results for the water layer model show that the Wenner-α array has an APE of 17.11%, the Wenner-β array has an APE of 12.16%, and that the Wenner-γ array has an APE of 16.21%.  Wenner-α is expected to produce an image with the best resolution having the highest APE, henceforth APE suggests the resolution capacity of an array

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

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

Pharmacognostic and Acute Toxicity Study of Burkea Africana Root

Burkea africana is a plant that belongs to then family Fabaceae; it is widely spread in tropical Africa including Nigeria. It is of valuable in  ethnomedicine especially in the treatment of antidote for venomous stings and bites, cutaneous and sub cutaneous parasitic infection, convulsion and pulmonary troubles. Despite the fact that roots of Burkea africana have several medicinal properties, no standardization parameter has been  assessed. Due to lack of standard parameters, proper identification and ascertaining quality and purity in the events of adulteration has been thwarted. The objective of the study was to establish some important pharmacognostic profile and safety margin of Burkea africana root with the hope of assisting in its standardization for quality, purity and safety. Elemental analysis was carried out using acid digestion method and phytochemical composition of the plants was evaluated using standard method. Acute toxicity was achieved using Lorke method to determine the LD50. Chemomicroscopical evaluation revealed the presence of cellulose, tannins, starch, lignin, calcium oxalate, suberin, aleurone grain and mucilage with the exception of calcium carbonate. The average moisture contents, total ash, acid insoluble, water soluble ash, alcohol extractive value and water extractive values in the powdered plant material were 3.8%, 7.5%, 4.43%, 8.07%, 25.0% and 20.33% respectively. In addition, Fe, Mn, Ni, Pb, Cd and Cu were found to be within the safety limit. Phytochemicals which include alkaloids, flavonoids, saponins, tannins, carbohydrates and triterpenes were detected in both aqueous and methanolic extracts. The LD50 of Burkea africana was found to be greater than 5000 mg /kg and could be considered safe for consumption. Keywords: Elemental analysis, Burkea africana, Pharmacognostic, Phytochemica