Showing papers in "Journal of Advanced Transportation in 1994"

Modeling probability distribution of delay at signalized intersections

Abstract: Accurate estimation of vehicle delay is difficult because of the randomness of traffic flow and large number of factors affecting intersection capacity. Existing delay models simplify the real traffic conditions and provide only approximate point estimates of average delay, whereas its variability should also be of interest. A stochastic model was used to study the changing probability distribution delay. The model is based on sequential calculation of queue length probabilities with any type of arrival process. Delay probability distribution was investigated for different degrees of saturation, arrival types and control conditions. The variance of delay increases rapidly with degree of saturation and is inversely proportional to the approach capacity. Other parameters such as cycle time and saturation flow do not have a significant effect on delay distribution. Both the mean and variance of delay are sensitive to arrival process characteristics and increase with the variance of arrivals.

Overflow queues and delays with random and platooned arrivals at signalized intersections

Abstract: The traditional two-term analytical model for predicting delays, queues and stops with random arrivals as found at isolated signalized intersections is extended to the case of platooned arrivals. The work was carried out in the context of modeling traffic performance at signalized paired intersections. A cycle-by-cycle macroscopic simulation model was used to calibrate the overflow terms of the performance formulae for a single stream of platooned arrivals at the downstream approach of a paired intersection system. The steady-state form of the analytical model was used for calibration. The parameters derived for the steady-state model are then used in the time-dependent form of the model. Descriptions of the general analytical model, the cycle-by-cycle simulation model, its validation against several well-known models are presented, and the new models derived from this study are described. Extension of the model to multistream, multiphase applications is discussed and areas of further study are identified.

An evaluation of vehicle deceleration profiles

Abstract: Vehicles stopping at signalized intersections were examined for the purpose of evaluating the validity of the common assumption of constant and uniform deceleration rates. The data set consisted of the first vehicles to stop upon the onset of the yellow signal interval with measurements of the initial approach speed, deceleration time, and deceleration distance. The deceleration rate may be computed using only two of the three measured values; thus the rate for each vehicle can be determined by three differnt equations. With nonuniform deceleration profiles, the equations will produce different values; and the degree of nonuniformity can be determined by comparing the differences in the computed deceleration rates. The analysis of the field observations indicated that 69% of the vehicles demonstrated deceleration profiles associated with nonuniform deceleration rates. Furthermore, the deceleration profile and the degree of nonuniformity were found to be a function of the initial approach speed.

The Role of the Physical Environment in Child Pedestrian Accidents

Abstract: The injury of a child pedestrian by a motor vehicle is the result of a complex combination of circumstances involving elements of child behavior, the behavior of the driver of the vehicle and a host of environmental factors. This paper reports on a study of the significance of physical environmental factors on children's' pedestrian accidents, using data drawn from 786 police reports on child pedestrian accidents occurring on the Island of Montreal between October, 1980 and March, 1982. A series of statistical tests are conducted to examine the effect of temporal variables (month, day, time of day), pedestrian characteristics (age, sex), accident location descriptors (intersection, mid-block, etc.) and environmental characteristics (adjacent land-use, Toad type, etc.). Remedial measures that are expected to be most effective in reducing the incidence of child pedestrian accidents in large urban areas are proposed.

A new algorithm for optimal signal control in congested networks

Abstract: Optimization of traffic lights in a congested network is formulated as a linear programming problem. The formulation adapted here takes into account particular capacity constraints for road links and for intersections. A necessary prerequisite for the determination of optimal green times is that representative a-priori information about the origin-destination and route choice pattern inside the network is available . Because any particular control strategy temporarily alters the effective turning rates at intersections, an iterative procedure is proposed here which accomplishes convergence of optimal signal control and resulting O-D flows. The efficiency of this optimization procedure is demonstrated in a case study for a network with 15 intersections.

Priority for public transit in germany

Abstract: Priority for public transit includes a large variety of measures, including improvements to infrastructure and vehicles. For vehicles, the low floor concept is of particular importance. The central points of priority measures, however, are improvements of traffic control by traffic signals. Here, an improved sensitivity regarding public transit vehicles is the key to a remarkable reduction of factors causing delays. Different techniques for a traffic actuated signal control and different strategies regarding the degree of priority are applied. Thus, especially the reliability of public transit operations is increased. The priority efforts must be embedded in an integrated plan covering the whole urban or metropolitan transportation system.

Safe design of personal rapid transit systems

Abstract: The safety of personal rapid transit systems involves careful attention to all features of the design such as the use of a hierarchy of fault-tolerant redundant control systems, bi-stable fail-safe switching, back-up power supplies, vehicle and passenger protection, and attention to the interaction of people with the system. Safety, together with reliability and adequate capacity, must be achieved while making the system economically attractive, hence techniques to achieve these goals at minimum life-cycle cost are primary in PRT design. Building on theory of safe, reliable, environmentally acceptable, and cost-effective design of PRT systems developed during the 1970's, in 1981 the author and his colleagues initiated design of a new PRT system, now called Taxi 2000. The paper describes the relevant features of Taxi 2000 and principles of safe design incorporated into it.

Planning for pedestrian networks in North American downtowns

Abstract: While North American urban regions are served by mechanical modes of transportation, downtowns are largely pedestrian environments. The growth and consolidation of office districts over the last twenty years have revived interest in developing coherent and efficient pedestrian networks, which can be coordinated with other transportation needs within the downtown. Ambitious plans for expansion of the downtown for offices, the retail and service industries as well as for housing and entertainment have been adopted in many North American cities during the 1980s. The successful integration of these large central areas depends to a considerable extent on the implementation of expanded pedestrian networks. This paper discusses certain spatial characteristics of North American cities which call for specific network designs and research into the walking environments of central areas. More knowledge is needed of the relative contributions to pedestrian regeneration of land use combinations, the design of networks and of walking paths. Language: en

Comparison of results of two models of transportation demand in hong kong: cdam and a version of microtrips

Abstract: CDAM is a new computer program for solving the combined trip distribution and assignment model for multiple user classes, which enables transport planners to estimate consistent Origin-Destination (O-D) matrices and equilibrium traffic flows simultaneously if the trip production and attraction of each user class at zone centroids are available. This paper reports an application of CDAM to the central Kowloon study area in Hong Kong. The coefficients of the model related to the components of generalized costs are calibrated on 1986 travel data. A comparison of results of CDAM and a version of MicroTRIPS models of transportation demand in Hong Kong are presented. Finally, some conclusions are drawn and the advantage of the CDAM are discussed.

Child pedestrian fatalities: the size of the problem and some suggested countermeasures

Abstract: The child pedestrian death rates, per 100,000 population, for the USA and 22 European countries are compared. The safety measures used in some of these countries, for the two key areas of danger for children, the school journey and the residential environment, are outlined. Problems that might prevent the introduction of these countermeasures in some other countries are discussed. It is recommended that: 1) there should be special low speed limits on the roads outside all schools. On minor roads traffic calming measures would be suitable, on main roads new speed limits could be introduced and enforced by police surveillance using video camera techniques. 2) In suitable residential areas children should be enabled to play out in safety on the streets near their homes. In some countries the most acceptable way of achieving this might be by a change in the law whereby children would have priority in these designated Home Zones.

Safer signalized junction design and self‐optimizing control

Abstract: The UK Transport Research Laboratory has long had a worldwide reputation for contributions to the field of traffic signal control, especially as originators of the TRANSYT and SCOOT signal coordination methods. This article describes some less known work. Accident risk at urban junctions and on road links between them is related to a wide variety of factors including: traffic and pedestrian flows, signal control parameters, geometry, and other layout features. Comprehensive studies have derived, and are continuing to derive, quantitative risk relationships for use in off-line software. Those for individual signalized cross-roads have already been incorporated in the TRL's program OSCADY to assist junction design. Now, an area-wide safety model incorporating the CONTRAM traffic assignment program is being actively developed to provide a tool for evaluation of network traffic management schemes. For on-line signal control at individual junctions, the MOVA system has been developed to provide a delay-minimizing or capacity-maximizing control logic as appropriate. 'Before and after' comparisons with the UK's previous fully vehicle-actuated signal system are presented, including both delay and safety aspects.

Cost-based approach for sizing of pedestrian facilities

Abstract: Pedestrian facility size is currently determined in direct relationship to the design level of service. However, the design level of service is chosen arbitrarily from the six levels of service, which are assumed to represent the freedom available for movement at different levels of pedestrian flow. This direct and simple approach to facility sizing is shown to have two fundamental deficiencies that contribute to wasteful over capacity. In this article, a cost-based approach is introduced to overcome the deficiencies. Two analytical models, one for determining optimal design density and another for determining optimal design flow, are presented. The optimum design parameters minimize the total cost of the facility defined as the sum of construction cost and user cost. The sensitivity of the optimum parameters to the cost and pedestrian flow parameters is demonstrated using a numerical example.

Impacts of regional transportation improvements on urban development in Japan

Abstract: Urban agglomerations in Tokyo and Osaka in post-war period are largely attributable to the policies underlying the four National Development Plans implemented in that period. These policies, which were originally intended to achieve an effect on the opposite of agglomeration, relate primarily to the high-speed transit network known as the Tokaido shinkasen and the expressway segments linking the Kanto and Kansai regions. For the purpose of capturing the historical scenario of regional agglomeration, we have formulated a long-term macro-econometric model from 1950–85, with 5-year simulation cycles. This constitutes an employment distribution block, an input-output block, and an inter-prefectural activities block, incorporating all major macro-variables. In an earlier stage of this research the model was calibrated and the total tests upon all formulations were completed. Ascertaining that the accuracy of the model is well within permissible limits, an evaluation of policy scenarios due to the delay in the introduction of the shinkansen on the Tokaido line, has been conducted. Results indicate that Tokyo grows much less rapidly than in reality, Osaka maintains the same rate of growth, and the other areas show a substantial growth by 1985. In the present version, we improve on the model with respect to its qualitative performance by relaxing the exogeneity of national employment and GNP to allow for the evaluation of these policy variables. In completing these final tests on the model, we are able to confirm the validity of the model by demonstrating its accuracy to be in a satisfactory range. In a case study, the policy areas that have contributed to the present distribution of development have been explored in detail. Comparative policy transformations, necessary to achieve the opposite effects to agglomeration, are discussed.

Facing the Realities of Non-Motorized Transportation in Developing Countries

Abstract: The objective of this paper is to assess issues concerning non-motorized transportation in developing countries. This assessment is done through an examination of three topics: a brief overview of the transportation picture in developing countries; a study of city size and city form vis-a-vis pedestrian movement; and, a look at the characteristics of non-motorized modes, including their capacities. An analysis and discussion attempt to sort out the crucial issues connected with pedestrian planning in particular, and non-motorized transport in general. It is concluded (1) that special attention be paid to space/time capacity/cost issues connected with non-motorized modes (2) that some of the low-cost intermediate technology modes be examined for possible inclusion in traffic streams (3) that land-use patterns need to be rearranged keeping in mind the limitations of non-motorized modes, and (4) that the extent to which physical trip-making can be substituted by telecommunication needs to be examined very critically. An agenda for action reflects these concerns.

Alterations to the transyt-7f model to represent near-side transit stops

Abstract: Transit vehicles stopping to load/unload passengers on-line at a signalized intersection can obstruct the flow of other vehicles. The TRANSYT model ignores the delay to other traffic caused by this loading/unloading process. This can cause TRANSYT to use incorrect flow profiles, resulting in signal timings that cater to these profiles rather than the actual ones. This paper describes a new model for representing near-side transit stops in lanes shared by public transit and private vehicles, and its implementation into the TRANSYT-7F program. The results of an initial application of the proposed model are also described. The proposed model, which is a deterministic simulation model, is able to represent the effect of near-side transit stops on the other traffic; this representation covers both total and partial blockage of the approaches during the transit loading. The procedure has been incorporated into the TRANSYT-7F program. This allows appropriate representation of the adverse effects of transit loading on-line during a green phase. It thus encourages the TRANSYT optimizer to push transit loading to the red phases.

Profile of the accident prone older driver

Abstract: Accident histories and other related records of elderly drivers were used to develop a profile of the accident prone older driver in Michigan Elderly drivers were defined as drivers with age greater than or equal to 65 years The variables used in the study were developed by stratifying drivers age, sex, and residency; type of accident and violation; and number of traffic infraction points received Comparisons were made between these strata, and the statistical significance of observed patterns in cross tabulated data was tested by performing the chi-square test The results of the study indicate that, by and large, the elderly drivers from urban areas as compared to those from rural areas, and male drivers as compared to females are more likely to be cited for traffic violations The statistical analysis showed some recognizable traits of the ''young'' elderly drivers that suggest prioritized safety countermeasures oriented toward them Language: en

Advanced transportation economic development

Abstract: Transportation has been one of the fields proposed as a likely candidate for both improvements and jobs. The issues of economic development associated with mass transportation characteristic of urban and interurban environments are addressed.