查看更多>>摘要：A procedure that can be used to compare a variety of common interchange types or make decisions about their design is described. The technique is based on the critical movement analysis approach traditionally used for signalized intersection analysis. This approach defines the rules for quantifying the sum of critical flow ratios for various interchange types. The concept of interchange delay is defined, and an equation for quantifying it is described. Simulation data are used to calibrate a series of models that relate the sum of critical flow ratio to interchange delay. A procedure that describes how these models can be used to obtain a quick estimate of the delay associated with a particular interchange type, given specific volume levels, lane assignments, and ramp separation distances, is documented.
查看更多>>摘要：Interchange ramp terminals are critical components of the highway network. They provide the connection between various highway facilities (e.g., freeway-arterial and arterial-arterial), and their safe and efficient operation is essential. The objective of this research was to develop improved methods for capacity and quality-of-service analysis of interchange ramp terminals. The research focuses on at-grade intersections but not on the freeway proper. All geometric configurations and interchange types except trumpet interchanges are considered, and the scope of the research includes only signalized interchanges and not "Stop" sign-controlled interchanges and roundabouts. The development of the analytical methodology is primarily based on simulation. The reason for using simulation is that adequate samples of field data are not available, and it is prohibitively expensive to collect them for all types of interchange configurations. The research team assessed several simulation models that were identified as capable of simulating all types of interchange ramp terminals and selected the most appropriate one for model development. Once a simulation model was selected, a variety of interchange configurations were simulated, and selected measures of effectiveness were obtained. Analytical models were developed on the basis of the results of simulation to predict different measures, such as average control delay, volume-to-capacity ratio, and queue-to-storage ratio, for a variety of design and traffic control characteristics.
查看更多>>摘要：This paper presents the results of a study that compared drivers' assessments of the performance of urban streets with objective measures of performance, including level of service (LOS). The purpose of the study was to test the ability of LOS to predict drivers' perceptions of service quality. Seventy-seven automobile drivers rated the service quality of half-mile segments of urban streets as depicted on videotaped scenes from the driver's perspective. Drivers rated 12 to 15 video segments on a six-point scale from very satisfactory to very unsatisfactory. After rating all segments, the drivers selected and ranked from a list of 36 factors the three factors that they considered the most important to quality. The results show that the mean driver rating had statistically significant correlations with operational and design characteristics and aesthetics, including the following variables: travel time, average travel speed, number of stops, delay, number of signals, lane width, the presence of trees, and the quality of the landscaping. LOS, calculated by the Highway Capacity Manual methodology, predicted 35% of the variance in mean driver rating. This finding suggests that LOS does not completely represent drivers' assessments of performance because drivers perceive the quality of urban street segments in several dimensions, including travel efficiency, sense of safety, and aesthetics.
查看更多>>摘要：Two-way stop control is a form of intersection operation in widespread use. Calculations of the level of service are usually based on gap acceptance theory. In the American Highway Capacity Manual, the influence of pedestrians is considered an impedance factor, whereas in the German guideline the influence of pedestrians and bicyclists has not been considered so far. To close this gap, an alternative calculation method, called the conflict technique, has been developed. This method allows consideration of the influence of nonmotorized road users on the traffic performance of motor vehicles. Moreover, the method provides a significant simplification of the entire theoretical approach. Different modalities of operation, such as a zebra crossing at the entries to an intersection, can be considered, as can the fact that some road users do not comply with the priority rules. It is possible to calculate the capacity for one movement from the minor stream from a single equation. To calibrate the calculation method, traffic at several intersections was observed by video and analyzed for traffic volumes, delays, compliance with priority rules, and other parameters. With these field measurements, the calculation method was calibrated to actual road-user behavior. Comparison of the conventional calculation concept based on gap acceptance and the new conflict technique showed that they provide similar results. In particular, the consideration of pedestrians and limited priority effects is a considerable benefit of the new method.
查看更多>>摘要：Traffic data were collected from 11 work zones on Interstate highways in Illinois in which one of the two lanes was open. The reductions in free-flow speed (FFS) due to narrow lanes and lateral clearances in work zones were studied. It was found that the reductions in FFSs of vehicles in work zones because of narrow lanes were higher than the reductions given in the Highway Capacity Manual for basic freeway sections. The data also showed that the narrower the lane was, the greater the speed reduction was. The data showed that the FFSs of heavy vehicles were statistically lower than the FFSs of passenger cars, even though the speed limit was the same for both types of vehicles. In addition, the reduction in the FFSs of heavy vehicles was greater than the reduction in the FFSs of passenger cars. This greater reduction in the speed of heavy vehicles affected the performance of the traffic stream in work zones. Thus, it should be considered in the computation of the passenger car equivalence for heavy vehicles. It is recommended that 10, 7,4.4, and 2.1 mph be used for speed reduction in work zones for lane widths of 10,10.5,11, and 11.5 ft, respectively.
Bruce W. LandisTheodore A. PetritschPeyton S. McLeodHerman F. Huang...
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查看更多>>摘要：This paper compares users' accommodation-based pedestrian level-of-service (LOS) ratings of signalized intersections in a video simulation environment and the physical roadway environment. Video simulation and walking course responses were compared with the use of data obtained from Walk for Science 2004, in which the participants reported their perceived level of safety and comfort as pedestrians. These data were used to test the hypothesis that subjects rate intersections' LOSs differently in a controlled (video simulation) environment than they do by walking along a real-world course and experiencing real-time traffic conditions. The results for intersections common to both experiences (549 observations) indicated a statistically significant difference in the respective ratings (t = 2.34). Accordingly, a calibration factor was developed to adjust the participants' scores from the video event to what they would have scored in the real-time field event. The adjusted video simulation data were then used to refine a field-calibrated model for pedestrian LOS at intersections (which is discussed in detail in another paper). Although further hypothesis testing may be conducted, the resulting general model for the pedestrian LOS at intersections is highly reliable, has a high correlation coefficient (R~2 = .73) with the average observations, and is transferable to the vast majority of metropolitan areas in the United States. This video simulation research design can serve as a model for similar data-gathering initiatives in the future as the effort to calibrate the modeling of video simulation data to field-based perception data continues.
查看更多>>摘要：Most users of the Highway Capacity Manual (HCM) would prefer to have confidence intervals around the estimate of delay, but no procedure measures the uncertainty in delay and level of service. Four sensitivity analysis methods—partial differential analysis (PDA), partial correlation coefficient analysis, standardized regression coefficient analysis, and the Fourier amplitude sensitivity test (FAST)—and four uncertainty analysis methods—first-order analysis (FOA), Monte Carlo simulation (MCS), FAST, and the point estimate method (PEM)—were investigated. They were applied to data from an actuated signalized intersection. All input variables in the delay model except for the duration of analysis period were considered uncertain, for consistency with HCM. Day-to-day variation was the source of errors. Progression factor, cycle length, green time, and saturation flow are the most sensitive parameters. The incremental delay and upstream metering factors are the least sensitive. Volume and peak hour factor fall in between. The four uncertainty methods produced similar results for the mean, standard deviation, and confidence intervals of control delay for the base case. When the standard deviations of input parameters were doubled, MCS, FAST, and PEM produced similar results. PDA and FOA appear to be less suitable for sensitivity and uncertainty analysis, respectively, of the HCM delay model for signalized intersections.
查看更多>>摘要：The Manual on Uniform Traffic Control Devices (MUTCD) contains the national standard for installing and maintaining traffic control devices on all streets and highways. The 2003 MUTCD contains numerous corrections, revisions, and updates to the millennium edition (2000). One update is related to the definition of crossing distance at signalized intersections, where the crossing distance is extended to the far-side curb rather than the center of the farthest traffic lane. This study investigated the sensitivity of intersection performance to crossing distance and walking speed, critical constraints in the determination of the minimum green time. Three crossing distance standards and four walking speeds are considered. With Highway Capacity Manual (HCM) procedures, the impacts of the given crossing distance definitions and walking speeds on intersection operations were tested on two intersection configurations over a range of cycle lengths and traffic volumes. The effect on intersection performance was found to be most significant at low cycle lengths, in some instances with the delay increased manyfold. However, when cycle lengths were increased to account for the pedestrian constraints, optimal delay rarely increased by more than a few seconds. Additionally, as the discrepancy between the critical lane traffic volume on the main and cross streets was increased, the impact of pedestrian green times on vehicle delay also increased. It was seen that as the cycle length increased, pedestrian minimum green times no longer governed, so the impact of pedestrians on intersection performance became increasingly insignificant, often with a minimal impact on the optimal performance.
查看更多>>摘要：In Florida, the increased use of restrictive medians and directional median openings has generated many U-turns at signalized intersections. There is no widely accepted procedure for estimating the effects of U-turning vehicles on signalized intersection capacity. In the 2000 edition of the Highway Capacity Manual, U-turns are treated as left turns for estimation of saturation flow rates. However, the operational effects of U-turns and left turns are different. This study analyzed the effects of U-turning vehicles on the left-turn saturation flow rate. Data were collected at three signalized intersections in the Tampa Bay area in Florida. In total, the study team recorded the queue discharge times for 260 queues, including 571 U-turning vehicles and 1,441 left-turning vehicles. On the basis of the data collected in the field, a regression model was developed to estimate the relationship between the average queue discharge time for each turning vehicle and the various percentages of U-turning vehicles in the left-turn traffic stream. Adjustment factors for various percentages of U-turning vehicles were also developed by using the regression model. The adjustment factors developed in this study can be directly used to estimate the capacity reduction due to the presence of various percentages of U-turning vehicles at a signalized intersection.
查看更多>>摘要：Current methodologies for estimation of intersection capacity are based mainly on the concept of saturation flow. Saturation flow is the steady maximum queue discharge rate after the green light is turned on. According to the U.S. Highway Capacity Manual, this steady maximum rate is generally reached after the fourth queuing vehicle is discharged. Two recent studies conducted in Hawaii and Taiwan, however, have found that queue discharge headways tend to undergo compression for a considerable time as more vehicles in the same queue are discharged. Consequently, queue discharge rates often kept rising even after the 15th vehicle has entered the intersection. If this queue discharge characteristic is common in the United States, then there is a need to assess the implications of continued use of the traditional concept of saturation flow rate for capacity analysis of signalized intersections. To provide insight into this potential problem, this study examines the queue discharge characteristics at three intersections on Long Island, New York. The queue discharge characteristics at all three intersections were found to be similar to those observed in Taiwan and Hawaii.
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