Highway Capacity Manual改訂の動向--テイラ-教授の講演より

Many different methods for the estimation of crtical gaps at unsignalized intersections have been published in the international literature. This paper gives an overview of some of the more important methods. These methods are described by their characteristic properties. For comparison purposes a set of quality criteria has been formulated by which the usefulness of the different methods can be assessed. Among these one aspect seems to be of primary importance. This is the objective that the results of the estimation process should not depend on the traffic volume on the major street during the time of observation. Only if this condition is fulfilled can the estimation be applied under all undersaturated traffic conditions at unsignalized intersections. To test the qualification of some of the estimation methods under this aspect, a series of comprehensive simulations has been performed. As a result, the maximum likelihood procedure and the method developed by Hewitt can be recommended for practical application.

Useful estimation procedures for critial gaps.

Present paper reviewed the past studies on pedestrian flow characteristics (such as speed, flow, density, space, free-flow speed and jam density) and development of Pedestrian Level of Service (PLOS) for various pedestrian facilities (i.e., sidewalk, walkway, crosswalk, grade separated, stairways and escalators). Fundamental relationships (between speed and density) were observed over different facilities and were found to be significantly different. The fundamental relationships for sidewalk facility predicted the range of free flow speeds to be 65 − 85 m / min and jam densities to be 3 . 5 − 5 . 3 ped / m 2 . The minimum and maximum pedestrian speeds over sidewalk facility in different countries observed were 52 m / min and 98 m / min respectively, with a mean speed of 79 m / min . The male pedestrians walked at 4 − 9 m / min higher speed in comparison to their female counterparts; while the older pedestrians walked at 15 − 20 m / min lower speed than the younger ones over the various types of crosswalk facilities. Similarly, speed-density relationships for ascending and descending stairways showed that the difference between the two directions varied between 4 − 12 m / min , and that the speed was significantly higher in case of descending direction. Moreover, the jam densities for stairways were also observed to be lower in case of descending direction, as the pedestrians generally maintain higher gap (than in ascending direction) with other pedestrians in front to avoid pushing and the risk of falling down. The flow characteristics were significantly influenced by the type of facility, width, age, gender and location of the study. Primarily factors such as physique (height), culture (dress), attractions (presence of hawkers located along sidewalks), friction (due to parked vehicles), purpose of walking trip and environmentl conditions were the main reasons for pedestrians of countries such as Saudi Arabia, Iraq, Bangladesh, Indonesia and Sri-Lanka to walk significantly slower than the counterparts pedestrians in the USA, UK or Canada. The review conducted on the PLOS mainly looked into the type of survey conducted (qualitative vs. quantitative), LOS parameters and the various software/models used in development of LOS. Researchers from the USA and Japan preferably used both qualitative and quantitative approaches in defining LOS over sidewalks; while in India, China and Malaysia qualitative method was highly preferred. Pedestrian volume, safety, surface, obstruction and width were observed as essential parameters for qualitative survey while density, flow rate, pedestrian speed and width were used in quantitative survey for sidewalks. In developing the PLOS over sidewalk facility; Conjoint analysis, Landis method, HCM method, affinity propagation cluster algorithm and Gainesville method were preferred by various researchers. Studies conducted over crosswalk facility measured space, flow rate, vehicle volume and delay as the most significant factors in developing LOS based on quantitative technique; while vehicle speed, pedestrian volume and traffic control were mostly used for LOS development using qualitative technique.

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Pedestrian flow characteristics and level of service on dissimilar facilities: A critical review

The pedestrian fundamental diagram, which describes the relationship between speed, flow and density, is one of the key concepts for the design of pedestrian facilities. It allows to determine the capacity of facilities as well as to calculate estimated walking times, for example when changing trains. In the last decades, laboratory and field measurements have been conducted to obtain the fundamental diagram for different situations. Based on this it was revealed that the fundamental diagram differs significantly between different locations and pedestrian compositions. Various parameters which significantly influence the shape of the fundamental diagram curve have been determined. Thus, poor results might occur when using a general form of the fundamental diagram for design purpose. Still, only either fundamental diagrams measured in a single setting or ones aggregating these measurements are available. No comprehensive model was found which is able to describe the differences observed as well as being able to estimate fundamental diagrams for other pedestrian compositions. Currently, an estimation of a specific fundamental diagram without corresponding empirical data is not possible. The idea of this thesis is to address this research gap by creating a generic model, which describes the main walking principles and the interaction between pedestrians. Using this model allows to generate situation specific fundamental diagrams. In addition, the underlying principles which determine the shape of the fundamental diagram are determined and the effect of different influence factors on human walking can be studied. By applying situation specific input parameter values, it shall be possible to generate situation specific fundamental diagrams useful for the design of pedestrian facilities. The model creation was done in two steps. As a basis for the quantitative fundamental diagram model, a qualitative generic walking model was developed. A comprehensive overview of the basic principles of walking and the interaction of pedestrian was given in the generic walking model. This was done by combining individual findings available in literature. Starting from a simple case, where a pedestrian is walking alone at constant speed, the model is extended to include all relevant influences on a pedestrian. The generic pedestrian walking model was then used as a basis for the fundamental diagram model. Here, a microscopic model was established where also the distribution of input parameter values can be simulated. Again, first a simple model was set up and complexity was added step by step. In the

A New Generic Approach to the Pedestrian Fundamental Diagram

Estimation of passenger car unit (PCU) values is very important for traffic capacity analysis and other relevant applications such as level of service (LOS) measures, determination of satur...

Review of Methods for Estimation of Passenger Car Unit Values of Vehicles

Estimation of passenger car unit (PCU) is a vital component of any traffic study conducted in developing countries owing to the heterogeneity in the vehicular traffic. Past studies on PCU factors a...

Three methods of PCU estimation at unsignalized intersections

Critical gap estimated at four Indian intersections using six popular techniques revealed a wide variation and many of these values are found to be unrealistically low It indicates that all these methods are not adequate to address the complex traffic behaviour that exists in heterogeneous and non-lane-based traffic environment A new method based on the occupancy time (OT) of a vehicle in the intersection area is proposed for the estimation of critical gap under mixed traffic conditions The method is demonstrated to provide reasonably good results when applied to the data collected at one intersection in the US also The correctness of the proposed method is further demonstrated by comparing the field capacity of a non-priority movement at one of the intersections with the theoretical capacity It is found that the proposed method gives the capacity which is closer to field capacity than those estimated by the maximum likelihood method or modified Raff method

Critical gap estimation at two-way stop-controlled intersections based on occupancy time data

Queue Clearance Rate Method for Estimating Passenger Car Equivalents at Signalized Intersection

This study explored the use of queue clearance rate method for estimating passenger car equivalent (PCE) at signalized intersections. PCE was estimated based on the assumption that the rate at which a queue of vehicles clears the intersection is a function of its composition. Results of this method were compared with the results estimated by some popular techniques. A four-legged intersection was simulated in VISSIM software and different techniques were used to convert the traffic mix into a uniform one. Parameters of VISSIM were modified to closely reflect the traffic behaviour under heterogeneous traffic conditions. All approaches of the intersection were loaded to saturated conditions and accuracy of estimated PCEs were established by comparing converted flow (PCE/h) with the capacity of an all-car traffic stream. Method based on saturation flow delivered the best result, but its use was limited to traffic composed only of two types of vehicles. Results of regression and optimization techniques were almost similar and the converted flow was close to the capacity of all-car stream. However, accuracy of these methods strongly relied on the correct measurement of saturation flow. Queue clearance rate method did not require value of saturation flow and yielded good estimates of PCE throughout the simulation runs. The maximum difference between the converted flow and capacity estimated with all car situations was found to be less than 10% in all cases considered in this study.

Queue clearance rate method for estimating passenger car equivalents at signalized intersections

Pedestrian facilities are provided to facilitate and encourage for short distance travel. The level of service (LOS) criteria available in the literature for pedestrian facilities are more adaptable to the pedestrian scenarios in the US than in a developing country like India. This paper presents the LOS criteria under two conditions, one for pedestrian movements along the carriageway on or at its side and another for the movement on a pedestrian facility. Data was collected in two different years (2007 and 2009) for the above mentioned two conditions. The LOS criteria were developed using two different approaches and the two data sets. One approach is based on the rate of change of curvature of the pedestrian flow-area module curve and another is based on speed ratio-density plot. It is observed that the pedestrian space criterion is more uniform and stable than the pedestrian flow criterion in defining the LOS of a facility. The suggested criterion for sidewalks and wide sidewalks will be very useful in revising the IRC codes on pedestrian facilities.

Mithun Mohan

Papers

Three methods of PCU estimation at unsignalized intersections

Critical gap estimation at two-way stop-controlled intersections based on occupancy time data

Queue Clearance Rate Method for Estimating Passenger Car Equivalents at Signalized Intersection

Queue clearance rate method for estimating passenger car equivalents at signalized intersections

Development of level of service criteria for pedestrians