PASSING EXPERIMENT ON TWO-LANE RURAL HIGHWAYS
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Abstract:
The major purpose of this study was twofold: (a) investigate the physical components of the overtaking maneuver on two-lane rural highways and the relationship between these components, and (b) evaluate whether current practices in highway design are adequate. Data for the study were collected by two instrumented vehicles driven simultaneously along two rural-road sections: the first car, the impeder, was overtaken by the second, faster car. Findings regarding the initial maneuver distance and time, space and time gap at encroachment onto opposing lane, distance traveled and time in opposing lane, space and time gap on completion of maneuver, speed differences, and acceleration characteristics are evaluated and discussed. Comparison of the findings with AASHTO values is presented, and it is concluded that the values given by AASHTO may be somewhat conservative. It is concluded that the passing maneuver should be studied more extensively, with the intention of re-reviewing current road-design guidelines.Keywords:
Overtaking
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In April 1990, the Transportation Association of Canada initiated a project to evaluate the effects of overall truck length on safety and level of service on two lane, two-way roads in Canada. The specific objectives were: 1) to determine if current intersection design and signal timing practices are adequate for vehicles longer than those presently permitted, and 2) to determine if current passing sight distances and pavement marking practices are adequate for overtaking vehicles longer than those presently permitted. Specific emphasis was placed on the implications of extending overall vehicle maximum length from 23 to 25 metres. The key findings were as follows: 1) an increase in maximum vehicle length from 23 to 25 metres would have little significant impact on the operation of intersections; 2) the impact of truck length on passing operations on two-lane highways is dependent on the geometric design standard and operating speed of the highway, and as the operating speed increases, the sight distance required to pass vehicles also increases; 3) at operating speeds over 80 km/h, the existing passing zone pavement markings may not provide adequate sight distance for passing 23 metre trucks, and an increase in maximum vehicle length to 25 metres would marginally increase this inadequacy; and 4) standards for passing sight distance and passing zone markings have traditionally been established based on one car passing another car, and it is recommended that these standards be reevaluated to take into account the maximum length of truck combinations in the Canadian fleet.
Overtaking
Sight
Geometric design
Daylight
Design speed
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In order to make the deceleration length more practical without compromising safety, a new concept left-turn lane design method was produced and was used on a new four-lane highway in Yunnan Province. We observed vehicles speed on a selected left-turn lane set up with the new concept and obtained speed data of normal section and split point. Then we analyzed the data by means of descriptive statistics analysis, the paired-samples T test and ANOVA. The result showed that the length of left-turn lane could be shorter than the specification without compromising comfort and safety. The speed used to determine the deceleration length could be reduced by 15km/h.
Turn (biochemistry)
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Variables in automobile design are discussed in relation to the present practices of marking no-passing zones on two- lane highways. One of the advantages in the recent increase in the horsepower of passing cars is the ability to complete passing maneuver in less time, thus reducing the possibility of being caught in the left lane of a 2-lane road with an oncoming vehicle rapidly reducing the time interval between life and death. This is closely allied with the lower height of the driver's eyes in the newer cars which, under certain highway conditions, reduces the distance that the driver can see a clear road ahead. Data were collected from a comprehensive series of investigations of passing practices on 2-lane highways. Detailed data were recorded for a total of 21,000 passing maneuvers at 32 locations in 7 states between 1938 and 1940. Data were obtained during recent studies by manual observations. The speeds of both the passed and passing vehicles were higher in 1957 than in 1938. However, the time spent in the left-hand lane by the newer vehicles in 1957 was 0.5 sec shorter than the time in 1938. The distance traveled in the left lane, increased 100 feet. It is concluded that there is little evidence to indicate that present practices of marking no-passing zones should be changed due to the changes that have taken place during the past years in vehicle design and driver performance.
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The safety implications of car-truck speed limits have not been adequately researched for two-lane highways. On two-lane highways speed controls can have a significant effect on vehicles interactions. Two different types of speed control strategies are considered: Uniform and Differential. Safety implications are considered using three overtaking-related indicators: Number of vehicles overtaking, 2) Percentage time spent in "desire to overtake mode", and 3) Average Time-to-Collision with the on-coming vehicle prior to returning to the original lane. Vehicle interactions affecting safety are estimated through the application of a calibrated microscopic traffic simulation model to a 6Km straight segment of two-lane highway.
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A highway need study was conducted in west virginia by reviewing speed studies on highways throughout the state. The operating speed on an existing highway is affected by design speed, traffic volume, and number of lanes. Also, for 2-lane roads, it is affected by the availability of sections on which the sight distance is of sufficient length to perform passing maneuvers safely. In the design of a new highway, it is the one factor which together with the traffic volume and assumed design speed determines the needed geometric features of a highway. An engineering analysis of the highway capacity requires the following information: (1) type of terrain through which the highway is located, (2) average highway speed and frequency of occurrence of sharp curves that cause abnormally low speeds, (3) percentage of the highway on which the passing sight distance exceeds 1500 feet, (4) the average truck factor and the truck factor on all long or steep grades, and (5) cross-section items such as shoulder and surface type, width, and condition. These items were determined for all highways in west virginia expected to carry annual volumes in excess of 1800 vehicles per day within the next 20 years.
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Geometric design
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State highway
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Operating speed
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Pavement markings have definite functions in a proper traffic control system. They are applied for the purposes of regulating and guiding the movement of traffic, and promoting safety without diverting the driver's attention from the roadway. It was observed that pavement markings located to the right of the car are detected more easily and at distances farther away when compared with the corresponding markings placed to the left of the car. However, compared to other types of longitudinal markings, the effect of edge lines on safety and driver behavior has been much less investigated. The conducted crash statistic analysis found that edge-line treatments on rural two-lane roadways may reduce accident frequency up to 26 percent and the highest safety impacts occur on curved segments of roadways with lane widths of 9 to 10 feet. The next stage was focused on complex investigations of edge lines impacts on driver behavior and reactions, including vehicle navigational and positioning issues, speed selection, and effect on driver visual perception. Stationary traffic observation, test driving, and several laboratory experiments were conducted on the selected rural two-lane highways with different roadway width before and after edge lines placement. Studies indicated that edge line treatments increase speed on average by 5 mph or 9 percent on both straight and curved highway segments; moves vehicles toward the pavement edge at both daylight and darkness in an average of 20 inches; reduce vehicle fluctuation around trajectory center line by 20 percent; reduce driver mental workload; improve driver's estimation of roadway curvature; and increase driver's advance time of intersection identification.
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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.
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The Pennsylvania Department of Transportation and other state transportation agencies are required to provide edge line delineation on two-lane arterials when traffic volume exceeds 6,000 vehicles per day and the pavement width is at least 20 ft. Other combinations of pavement width and traffic volume may also warrant edge line delineation. The standard edge line width is 4 in.; however, an edge line width of 8 in. can provide greater emphasis for motorists. There is a need to evaluate the effectiveness of providing wider edge lines on horizontal curves to determine if they provide improved delineation for motorists on two-lane highways. The objective of this project was to evaluate the operational effects of using wider edge lines on horizontal curves along two-lane rural highways. A before-after observational study with comparison sites was used to evaluate the change in several performance measures, including mean speed, speed variance, encroachment frequency, mean lateral vehicle position in the travel lane, lateral vehicle position variance, and speed and lateral vehicle position differential between the tangent and midpoint of a horizontal curve. Day and night time periods were considered as were approach tangent and horizontal curve locations. The effects of vehicles traveling in the opposing travel lane were also considered in the evaluation. The results indicate that wide edge lines, applied to horizontal curves on two-lane rural highways in Pennsylvania, do not consistently change the encroachment proportion along curves, nor do they consistently change driver behavior patterns at all treatment locations as measured by speed and lateral vehicle position. The location of speed deceleration, based on a subjective assessment of speed profile plots, provides evidence that drivers recognize curves at night from a greater distance with wide edge lines when compared to similar curves with standard, 4-in.-wide edge lines.
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AbstractAbstractTransition zones are defined as locations where the posted speed limit changes from high- to low-speed. On high-speed two-lane rural highways, transition zones are often encountered when the roadway approaches a built-up area. The purpose of this study was to collect operating speed, roadway, roadside, traffic control, and land use data along two-lane rural highway transition zones in central Pennsylvania. These data were used to estimate passenger car operating speed models, recognizing the hierarchical nature of the data-generating process. The results showed that a three-level model could capture site-level speed variance that could not be captured in a panel data modeling framework; however, the parameter estimates and standard errors were very similar when comparing the model estimation results. It was also found that the presence of horizontal curves, presence of warning signs, the presence of curb, and increased access density were associated with reduced vehicle operating speeds. Increasing the lane width, shoulder width, and lateral clearance to obstructions was associated with increases in vehicle operating speeds. The models estimated in this paper could be used as a starting point to develop transition zone design guidelines.Keywords: vehicle operating speedrural highwaytransition zonesspeed limit
Speed limit
Operating speed
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In April 1990, the Transportation Association of Canada initiated a project to evaluate the effects of overall truck length on safety and level of service on two-lane, two-way roads in Canada. The specific objectives were: 1) to determine if current intersection design and signal timing practices are adequate for vehicles longer than those presently permitted, and 2) to determine if current passing sight distances and pavement marking practices are adequate for overtaking vehicles longer than those presently permitted. Specific emphasis was placed on the implications of extending overall vehicle maximum length from 23 to 25 metres. The key findings were as follows: 1) an increase in maximum vehicle length from 23 to 25 metres would have little significant impact on the operation of intersections; 2) the impact of truck length on passing operations on two-lane highways is dependent on the geometric design standard and operating speed of the highway, and as the operating speed increases, the sight distance required to pass vehicles also increases; 3) at operating speeds over 80 km/h, the existing passing zone pavement markings may not provide adequate sight distance for passing 23 metre trucks, and an increase in maximum vehicle length to 25 metres would marginally increase this inadequacy; and 4) standards for passing sight distance and passing zone markings have traditionally been established based on one car passing another car, and it is recommended that these standards be reevaluated to take into account the maximum length of truck combinations in the Canadian fleet.
Overtaking
Sight
Geometric design
Design speed
Daylight
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