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Multiple Passing Maneuvers : New Design and Marking Criteria to Improve Safety
Abstract
Passing maneuvers can be single or multiple, depending on how many vehicles are involved. In a multiple pass, one passing (or fast) vehicle passes at least two impeding (or slow) vehicles, without returning to the own lane until the whole maneuver is completed. Consequently, the required gap in the opposing traffic is longer. Nevertheless, all passing sight distance criteria consider only single passing maneuvers, so they could be not enough to accommodate multiple passes. Besides, any author did not focused on the potential safety problem even though about 20% of observed passing maneuvers involved more than two impeding vehicles. An instrumented vehicle was used to collect data of single and multiple passing maneuvers in Spanish twolane rural roads. The instrumented vehicle circulated at a constant speed, slightly lower than the operating speed, in order to be passed by faster vehicles. The whole passing maneuver, as well as the following process, was registered. External observations at certain locations complemented the observational data. The results provided guidelines to formulate a new passing sight distance model, valid also for multiple passes. Passing distance on the left lane was 43% higher for double maneuvers, and passing time on the left lane, 36% longer. On average, final speed of passing vehicle was 4 km/h higher in double passes. These results estimated the required passing sight distance. The comparison of the model with the existing criteria showed that passing zones with sight distance and length close to minimum values do not provide enough space to pass more than one vehicle with safety.
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A mathematical model is derived for describing the critical nature of the passing maneuver on two-lane highways. This model is based on the hypothesis that a critical position exists during the passing maneuver where the passing sight distance requirements to either complete or abort the pass are equal. At this point, the decision to complete the pass will provide the same head-on clearance to an opposing vehicle as will the decision to abort the pass. Current highway practice in both designing and marking for passing sight distance uses a model that assumes that once a driver starts a pass, he must continue until the pass is completed. In other words, the model assumes that the driver has no opportunity to abort the pass. Because this hypothesis is unrealistic, the model derived here is recommended for determining new passing sight distance requirements for both designing and marking passing zones. Suggested values are given for these requirements. A brief analysis is also presented of the sensitivity of passing sight distance requirements to vehicle length. This analysis shows that the effect of truck length is not as dramatic as previously reported in the literature.
Most studies on two-lane highway operations have focused on the percentage of following vehicles or the adjustment of the Highway Capacity Manual (HCM) procedure to local data. The HCM proposes the length of no-passing zones as a model parameter; however, the distribution and characteristics of passing zones are not addressed. In fact, only a few studies on the expected number of passes in a passing zone have been carried out. This research presents an analysis of the effectiveness of passing zones in terms of their length and traffic volume. Data were collected from four passing zones on a rural highway in Spain. The two-way traffic volumes ranged from 100 to 900 vehicles per hour (vph), and the passing zone lengths ranged from 265 to 1,270 m. More than 1,600 passing maneuvers were recorded. The operational effectiveness of the passing zones was obtained from the passing frequency and the passing rate. The results indicated that the longer the passing zone, the higher the passing frequency; however, the results stabilized with lengths above 1,100 m. Balanced flows with two-way traffic volumes between 600 and 700 vph optimized the number of passes. Nevertheless, the increase in the passing frequency with the traffic volume was lower than with the increase in following vehicles. The results were validated with data from another 12 passing zones. Finally, HCM adjustments based on the percentage of no-passing zones did not reliably represent the effectiveness of passing zones. Therefore, the effectiveness of every passing zone should be considered, and adjustment factors should be modified to maximize the passing opportunities for traffic volumes between 600 and 700 vph.
Drivers need sufficient passing sight distance (PSD) to pass slower vehicles with safety. This distance can help to improve traffic operation on two-way, two-lane highways. Existing models propose different values of PSD because of different assumptions. In only some cases were these models based on field data of passing maneuvers. This research proposed the design of a methodology to observe passing maneuvers on existing highways with the help of six video cameras installed at a fixed point next to passing sections. The use of more cameras allows complete registration of trajectories along the entire passing zone, with uniform image resolution. The methodology was applied to register a sample of 234 maneuvers on four passing zones. Trajectories of 58 maneuvers were completely described and analyzed with specific restitution software. Results were compared with those from existing PSD models. The distances traveled proposed by the AASHTO model on the left lane were (a) similar to average observed distances when the passed vehicle was one truck and (b) between 50 and 100 m higher when one passenger car was passed. Higher differences, greater than 100 m, were found between measured data and the PSD model (published previously), especially at high design speeds. The observed average speed difference between passing and impeding vehicles was significantly higher than that in any model. Variables with the strongest influence on the time and distance traveled on the opposing lane were the type and speed of the passed vehicle and the length of the passing zone. Left-lane time and distance increase with this length.
Passing is one of the most complex driving maneuvers performed on two-lane rural roads and has important effects on road safety and traffic operation. Passing is affected by driving behavior, road geometry, traffic volume, and traffic composition as well as external factors. Research was developed to compare the passing process under daytime and nighttime conditions. An experimental method was designed to collect video data of passing maneuvers on a two-lane rural road segment located near Valencia, Spain. Two methods were used: (a) external observations of four passing zones with six video cameras and (b) an instrumented vehicle equipped with video cameras and laser rangefinders, driven slightly below the operating speed along a segment of the same road so it would be passed by other vehicles. A total of 291 maneuvers were observed, up to 20% of which were at night. Macroscopic analysis results indicated that approximately 17% of passes were at night, even though passing frequency and passing demand decreased at night. Also, the behaviors of individual drivers who passed other vehicles were different at night and during the day. Maneuvers limited by the presence of an opposing vehicle were performed more quickly at night, even if the accepted gaps were longer. In this case, a more difficult perception of distances to opposing vehicles and of vehicle speeds explained the differences. In contrast, maneuvers limited by sight distance (without a visible opposing vehicle) were slower at night. This observation matched a traditional hypothesis: passing at night is safer because the headlights of an opposing vehicle allow a driver to anticipate the vehicle's position before it becomes visible.
Overtaking is one of the most dangerous manoeuvres on two-lane rural highways. The most influential factors are related to drivers, so ITS and assistance systems are not yet common. This research is based on experimental data of overtaking manoeuvres collected using an instrumented passenger car, equipped with four cameras, laser rangefinders and a global positioning service (GPS) tracker. This vehicle was driven along four different road segments in the surroundings of Valencia (Spain) at a speed slightly slower than the operating speed of each segment. Overtaking time and speeds were measured. Unlike previous work, the influence of human factor was also considered. Age and gender of overtaking driver, as well as time spent following were used to characterise this influence. More than 200 manoeuvres were recorded and the influence of driver characteristics and delay on gap acceptance, manoeuvre duration and speed differences have been analysed. Results show differences in behaviour between age and gender groups, since young male overtaking drivers have shown a more aggressive behaviour. Overtaking times were around 1 s lower than other drivers, whereas average speed difference was 4 km/h higher. Collected data and their analysis have provided a basis to review design criteria and to develop future assistance systems.
Daytime high-speed passing maneuvers were recorded along a straight and flat 15-mi section of a rural two-lane, two-way highway in Texas. The posted speed limit was 70 mph. Passing maneuvers were covertly recorded from the overtaken vehicle, which was driven at three specific study speeds: 55, 60, and 65 mph. A total of 105 single-vehicle daytime passes were analyzed. Speed profiles of the passing vehicles' passes were developed for each of the three studied speeds. The results were compared with AASHTO's assumptions and criteria for minimum passing sight distance (PSD) for two-lane, two-way highways. In particular, the analysis focused on the elements associated with a passing vehicle while it occupied the opposing lane of travel. The specific elements that were studied included these four: the average passing speed, the speed differential between passing and passed vehicles, the distance traveled while making the pass, and the total elapsed time. The general findings provided support for the AASHTO PSD model. For the assumptions made, the model provided reasonable results. However, the assumptions may need to be updated or to have more flexibility added. For instance, for a 70 mph design speed, the assumed speed of the overtaken vehicle is 54 mph in the AASHTO PSD model. The PSD associated with these speeds was verified in this study. But what if the overtaken vehicle was traveling at 60 or 65 mph? The results of this study show that the current AASHTO PSD model would provide inadequate PSD values for overtaken speeds greater than those currently assumed.
The main purpose of this research was to develop models to quantify the major components of the passing process. A second goal was to compare the results with existing highway-design models and to arrive at conclusions about the applicability of the existing models. Additional objectives were to evaluate several time elements of the passing process, such as the response time of drivers from the arrival of a proper gap until the start of the passing maneuver. The evaluation is based on an analysis of data that were collected by videotaping six tangent two-lane highway sections from high vantage points and from a helicopter hovering above one site. Normal driver behavior was not disturbed during the data collection process. About 1,500 passings were recorded; of these, 54 percent were characterized as "single passing," in which one driver passed a single, slower vehicle. About half of all passing maneuvers were found to involve two cars; in the other half, at least one truck was overtaken. A model showing the relationship between the speed of the impeding vehicle and the passing distance was calibrated, and the implications for highway-design procedures were discussed. Several of the findings had unique safety implications, such as the very short headway before the start of the passing maneuver and very short driver-reaction times. The primary results of the analyses enabled determination of the required passing distances and, therefore, the sight distances needed for different design speeds and various traffic combinations. Additional safety-related aspects are evaluated and discussed.
The maximum permitted length of trucks in North America and other parts of the world has increased significantly over the past 20 years. This has led to concern regarding the interaction of trucks with other elements in the traffic stream. There are many highway infrastructure design criteria that need to be reassessed in light of recent evidence on the behavior and properties of trucks. One of them is the passing sight distance (PSD), which is crucial for a safe overtaking maneuver. In addition, to overcome the increased congestion of modem roads, the development of the Intelligent Transportation System also requires an on-line overtaking model, which is able to provide the desired trajectory for the control. This paper presents a mathematical model that enables the determination of the safe PSD and calculates the desired trajectory for overtaking on two-lane highways. In addition to vehicle length, 10 other parameters that have an effect on the PSD are also included in this model. Specifically, the effects of various input parameters have been examined. Simulation results from this model are compared with those suggested by the American Association of State Highway and Transportation Officials (AASHTO) to test the validity of the model. Also, we explain why the standards given in the AASHTO study of 1994 could be thought to be conservative.
This contribution presents the results of a microscopic traffic simulation study of the potential effects of an overtaking assistant for two-lane rural roads. The overtaking assistant is developed to support drivers in judging whether or not an overtaking opportunity can be accepted based on the distance to the next oncoming vehicle. Drivers have been found to consider this to be a difficult part of an overtaking manoeuvre. The assistant’s effects on traffic efficiency, driver comfort and road safety have been investigated using traffic simulation. The results indicate that this type of overtaking assistant can provide safety benefits in terms of increased average time-to-collision to the next oncoming vehicle during overtaking manoeuvres. This safety benefit can be achieved without negative consequences for traffic efficiency and driver comfort. A driver assistance system that supports the distance judging part of overtaking manoeuvres can therefore contribute to improved traffic conditions on the two-lane rural roads of the future.
Several models have been developed to determine the minimum passing sight distance required for safe and efficient operation on two-lane highways. The American Association of State Highway and Transportation Officials has developed a model assuming that once the driver begins a pass, he/she has no opportunity but to complete it. This assumption is believed to result in exaggerated passing sight distance requirements. Considerably shorter passing sight distance values are presented in the Manual of Uniform Traffic Control Devices and are used as the marking standards in Canada and the U.S.A. More appropriate models have been developed considering the driver's opportunity to abort the pass, and are based on a critical sight distance which produces the same factor of safety whether the pass is completed or aborted. However, these models need to be revised to determine the passing sight distance requirements more accurately and to closely match field observations. In this paper, a revised model for determining the minimum required passing sight distance was developed, based on the concept of critical sight distance and considering the kinematic interaction between the passing, passed, and opposing vehicles. The results of the revised model were compared with field data and showed that the revised model simulates the passing manoeuvre better than the currently-available models which are either too conservative or too liberal. The results showed that the passing sight distance requirements recommended in the Manual of Uniform Traffic Control Devices are sufficient at low design speeds (50-60 k.p.h.) and for manoeuvres involving passenger cars only. For higher design speeds, the Manual of Uniform Traffic Control Devices standards are less than the passing sight distance required for safe and comfortable passes. The deficiency was found to increase with the increase in design speed, and reaches about 36% at a 120-k.p.h. design speed. Based on these results, major revisions to the current Manual of Uniform Traffic Control Devices marking standards are recommended.