TRAFFIC CAPACITY THROUGH URBAN FREEWAY WORK ZONES IN TEXAS
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Findings of capacity studies conducted at urban freeway maintenance and construction work zones in Houston and Dallas are summarized. Studies were conducted on five-, four-, and three-lane freeway sections. The results indicate that the per-lane capacities are affected by the number of lanes open during the roadwork. For example, the average capacity on a three-lane section with two lanes open was 1500 vehicles per hour per lane (vphpl), whereas the average capacity with one lane open was only 1130 vphpl. Also illustrated is how the data can be used to estimate the effects of the lane closure. The results of the study can be used in scheduling work that involves lane closures on freeways. (Author)Keywords:
Highway Capacity Manual
Closure (psychology)
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For approximately ten years, the north Carolina Department of Transportation has used an adaptation of the Iowa Weave as a means to slow and control the traffic flow through highway construction zones. In this configuration, the open travel lane is switched into the lane that was originally closed in the advance buffer area of lane closures. A study of the effectiveness of these weaves follows here. This study is part of a larger research project undertaken by the NCSU Civil Engineering Department and the NCDOT to determine capacity and flow characteristics through freeway workzones and effective methods of modeling these zones.
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With the surge of traffic volume, more four-lane freeways have been converted into eight-lane freeways, which leads to a rise in vehicle driving freedom and complexity. Correspondingly, lane management strategy is employed to regulate traffic operation and thus modify road capacity. This paper investigates basic sections of an eight-lane freeway as the research object. Based on the operation data of the Shanghai-Nanjing freeway, a vehicle classification method taking rear-end spacing as the index was promoted, classifying vehicles into four kinds. Then by adopting empirical analysis and cellular automaton simulation model improved on vehicle division and lane changing rules, the eight-lane freeway capacity was studied and verified. Moreover, the impact of truck ratios and lane management strategies on capacity was specified. By conducting this research, it will be beneficial to control eight-lane freeway flow reasonably as well as improve operational efficiency and safety.
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This paper reports findings from recent investigations into freeway capacity at several reconstruction zones in Ontario, Canada. The aim is to provide guidelines for estimating freeway capacity at reconstruction sites. Findings are presented in two parts. The first involved results of individual investigations to estimate a base capacity at freeway reconstruction sites and the individual effect of several important factors that are believed to affect this capacity, namely; the effect of heavy vehicles, driver population, rain, site configuration, work activity at site, and light condition. In the second part, attempts to model work zone capacity are presented. Initially, two types of "site-specific" capacity models were developed using different analytical techniques at sites that have the most extensive and comprehensive capacity data. Finally, a "generic" capacity model for freeway reconstruction sites is proposed based on results from the individual investigations and the site-specific models. The proposed model suggests a base capacity value of 2,000 passenger cars per hour per lane for reconstruction sites under favorable conditions. Heavy vehicles and driver population were found to have the most significant effect on capacity.
Carrying Capacity
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The findings of a limited study aimed at examining the basic characteristics of freeway traffic flow at construction zones are presented. The intent is to expand the scope of previous research efforts in this area, which have focused on the determination of point estimates of work zone capacity, under a variety of freeway lane configurations upstream of and in the vicinity of the work area. Field studies conducted in Illinois, encompassing more than 21,000 vehicle observations, were used to examine the entire range of the speed-flow relationship in the open lane of traffic. A normalizing procedure was devised to isolate and quantify the impact of work zone activity descriptors, such as the location of work relative to the traveled lanes, crew size, equipment, and other pertinent parameters, on the observed traffic speed. It was found that the effect of work activity on traffic flow is significant in periods of (a) high approach flow rates, (b) high truck percentages, and (c) intense work activity near the traveled lanes.
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Speed limit
Highway Capacity Manual
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This paper uses the method of kinematic waves, developed in part I, but may be read independently. A functional relationship between flow and concentration for traffic on crowded arterial roads has been postulated for some time, and has experimental backing (§2). From this a theory of the propagation of changes in traffic distribution along these roads may be deduced (§§2, 3). The theory is applied (§4) to the problem of estimating how a ‘hump’, or region of increased concentration, will move along a crowded main road. It is suggested that it will move slightly slower than the mean vehicle speed, and that vehicles passing through it will have to reduce speed rather suddenly (at a ‘shock wave’) on entering it, but can increase speed again only very gradually as they leave it. The hump gradually spreads out along the road, and the time scale of this process is estimated. The behaviour of such a hump on entering a bottleneck, which is too narrow to admit the increased flow, is studied (§5), and methods are obtained for estimating the extent and duration of the resulting hold-up. The theory is applicable principally to traffic behaviour over a long stretch of road, but the paper concludes (§6) with a discussion of its relevance to problems of flow near junctions, including a discussion of the starting flow at a controlled junction. In the introductory sections 1 and 2, we have included some elementary material on the quantitative study of traffic flow for the benefit of scientific readers unfamiliar with the subject.
Kinematic wave
Three-phase traffic theory
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Recommendations on estimating the capacity of short-term freeway work zone lane closures are presented. The recommendations are based upon 45 hours of capacity counts at 33 different work zones between 1987 and 1991. These new data indicate average capacities for short-term freeway work zone lane closures from 3 to 1 lanes and from 2 to 1 lanes that are significantly higher than older values reported in the 1985 Highway Capacity Manual. A base capacity value of 1,600 pcphpl is recommended for all short-term freeway work zone lane closure configurations. Adjustments are recommended for the effects of the intensity of work activity, percentage of heavy vehicles in the traffic stream, and presence of entrance ramps near the beginning of the lane closure. It is recommended that the new base capacity value and adjustments be used in lieu of the current procedures in the 1985 Highway Capacity Manual.
Highway Capacity Manual
Closure (psychology)
Work zone
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Highway pavement maintenance is very expensive not only in terms of costs to the responsible agencies but also in terms of disruptive delays to users. Construction and maintenance activities on four-lane highways (with two lanes in each direction) often require the closure of one of the two travel lanes. Longer work zones tend to increase the user delay costs. Maintenance work can be performed more efficiently, i.e., with fewer repeated setups, in longer zones. A relatively simple mathematical model is developed to optimize work zone lengths on four-lane highways where one lane in one direction at a time is closed. The objective is to minimize the total cost, including the agency cost, the accident cost, and the user delay cost. The optimized variable (e.g., work zone length) and the sensitivity results generated from a numerical example are presented in this study. With user-specified input parameters, this model can be used to optimize work zones on four-lane highways for a wide variety of circumstances.
Work zone
Closure (psychology)
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An important aspect of a highway work zone is the lane-closure strategy and the movement of traffic through the work zone. As part of the evaluation to determine the effects of different lane-closure strategies (e.g., one-, two-, or three-lane closures on a four-lane section), the additional costs to vehicle users should be considered. It is therefore necessary to have a model that will improve the accuracy of user cost estimates resulting from the forced movement through a restricted work zone. A computer model, Queue and User Cost Evaluation of Work Zones (QUEWZ), developed to estimate the additional user costs resulting from lane closures in one or both directions of travel is described. User costs can be estimated when one or more lanes are closed in just one direction of travel or when a crossover is used. Hourly as well as daily user costs are estimated, and when vehicle demand exceeds capacity, the model also estimates the length of queue. The model is designed specifically for freeway conditions, but it can be used in other situations if appropriate adjustments are made in the input data. Two vehicle types are used in the model--passenger cars and trucks.
Work zone
Closure (psychology)
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The objectives of this study were to investigate various independent factors that contribute to capacity reduction in work zones and to suggest a new methodology to estimate the work zone capacity. To develop the new capacity estimation model, traffic and geometric data were collected at 12 work zone sites with lane closures on four normal lanes in one direction, mainly after the peak-hour during daylight and night. The multiple regression model was developed to estimate capacity on work zones for establishing a functional relationship between work zone capacity and several key independent factors such as the number of closed lanes, the proportion of heavy vehicles, grade and the intensity of work activity. The proposed model was compared with other existing capacity models, and showed improved performance for all of the validation data.
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