Downstream Bottleneck Research Articles

Queuing and Statistical Analysis of Freeway Bottleneck Formation

A modified approach to treat traffic flow parameters (flow, density, and speed) has been introduced in this paper. A queuing analysis has been conducted on traffic flow data on Interstate 94 in the Minneapolis–St. Paul metro area. A methodology has been developed to calibrate loop detector count data. Corrected flow data has been subjected to analysis using queuing analysis to compute densities and speeds on freeway sections. Statistical analysis identifies “active bottleneck” locations on freeways and sections where bottlenecks occur because of disturbances caused by downstream bottlenecks propagating backwards in the form of shockwaves. A sample of 6 days on Interstate 94 was considered for the analysis. Our analysis reveals that the same section cannot always be characterized as a “bottleneck” location; at some times it is active and at others it is subject to downstream bottlenecks. Traffic flow characteristics change and that leads to changing situations on each freeway section.

Microscopic theory of spatial-temporal congested traffic patterns at highway bottlenecks.

A microscopic theory of spatial-temporal congested traffic patterns at highway bottlenecks due to on-ramps, merge bottlenecks (a reduction of highway lanes), and off-ramps is presented. The basic postulate of three-phase traffic theory is used, which claims that homogeneous (in space and time) model solutions (steady states) of synchronized flow cover a two dimensional region in the flow-density plane [B. S. Kerner, Phys. Rev. Lett. 81, 3797 (1998); Trans. Res. Rec. 1678, 160 (1999)]. Phase transitions leading to diverse congested patterns, pattern evolution, and pattern nonlinear features have been found. Diagrams of congested patterns, i.e., regions of the pattern emergence dependent on traffic demand, have been derived. Diverse effects of metastability with respect to the pattern formation have been found. The microscopic theory allows us to explain the main empirical pattern features at on-ramps and off-ramps which have recently been found [B. S. Kerner, Phys. Rev. E 65, 046138 (2002)]. (i) Rather than moving jams, synchronized flow first occurs at bottlenecks if the flow rate is slowly increasing. Wide moving jams can spontaneously occur only in synchronized flow. (ii) General patterns (GP) and synchronized flow patterns (SP) can spontaneously emerge at the bottlenecks. There can be the widening SP (WSP), the moving SP (MSP), and the localized SP. (iii) At on-ramps cases of "weak" and "strong" congestion should be distinguished. In contrast to weak congestion, under strong congestion the flow rate in synchronized flow in GP reaches a limit flow rate, the frequency of the moving jam emergence reaches a maximum, i.e., the GP characteristics under strong congestion do not depend on traffic demand. (iv) At the off-ramp GP with weak congestion occur. (v) A study of the pattern formation on a highway with two bottlenecks shows that diverse expanded patterns can occur, which cover both bottlenecks. SP first emerged at the downstream bottleneck can be caught at the upstream bottleneck (the catch effect). MSP, WSP, or wide moving jams first emerged at the downstream bottleneck induce diverse patterns at the upstream bottleneck. The onset of congestion at the upstream bottleneck can lead to an intensification of congestion at the downstream bottleneck. This causes a change in the pattern type and/or the pattern features.

Total quality management versus business process re-engineering: A question of degree

An increasing number of manufacturing organizations are placing direct emphasis on operations improvement as a means of achieving competitive success. Small and medium enterprises (SMEs), however, generally lack the resources in capital, time and expertise to implement business process re-engineering (BPR), as has been advocated by a number of authors. This paper presents a comparative analysis of continuous improvement (CI) versus BPR approaches to operational change. Change implies risk, and SMEs naturally require a means for establishing levels of uncertainty and net return. Equally, the performance measures adopted by these two (respectively, bottom-up and top-down) approaches differ significantly and normally defy direct comparison. A dynamic systems simulation is developed from a case study within the plastics industry and is used to evaluate the implementation of either varying levels of improvement or natural processes in the case of BPR. Although it is an industry-specific model, the approach raises several implications. Of specific interest is the trade-off between performance improvement and cost, time frame and risk. Attention is also focused on evaluation of the threshold at which the two philosophies overlap and the point at which companies may make the transition between the two philosophies. The paper goes on to evaluate the decrease in the return of investment (ROI), as improvements impinge on other stages within the process, creating up- and downstream bottlenecks. It also evaluates the level of a single ‘natural process’, as a means of costing BPR implementation. The paper concludes with the definition of ROI curves, which are intended to inform SMEs in the selection of appropriate improvement strategies.

Coordination of traffic management instruments using agent technology

The objective of this paper is to prove by example the opportunities for cooperation between dynamic traffic management instruments. Agent technology is presented as a useful way to support the deployment of these ideas. In the Netherlands, more and more instruments are installed to promote the flow of traffic. As more and more instruments are deployed, chances are that conflicts will arise when control tools are applied in the same area. The increase in the number of the deployed instruments implies a bigger responsibility for the Dutch Traffic operators, who will have to ascertain which control scenarios are relevant to the situation at hand and implement them. By modeling the separate instruments as intelligent agents, it might be possible to tune the actions of the individual instruments through the agent concept of collaboration. Letting the individual instruments handle the most basic forms of coordination automatically might also relieve the traffic operator. This paper will demonstrate the aforementioned ideas using two simple examples: one in which consecutive ramp metering installations coordinate their actions to promote the flow at a downstream bottleneck and one in which traffic management instruments coordinate their actions to attain a common goal on the network-level.

Improvement of "hit-to-lead" optimization by integration of in vitro HTS experimental models for early determination of pharmacokinetic properties.

Development of predictive in vitro surrogate methods for traditional approaches assessing bioavailability and pharmacokinetics of lead compounds must be made to both keep pace with high-throughput (HT) lead identification and to mitigate the high costs associated with progression of compounds with poor chances of developmental success. Indeed opportunities for improvement still exist in the lead optimization phase versus the lead identification phase, where HT methodologies have been nearly optimized. Review of examples, limitations, and development of high-throughput microtiterplate-based assays for evaluating metabolic liabilities, such as in vitro radiometric and fluorometric assays for inhibition of cytochrome p450 (CYP) activity, determination of stability of a compound in liver microsomes, or cloned CYPs coupled to reconstituting systems are described. Parallel approaches to improve speed, resolution, sample preparation, as well as data analysis using LC/MS and LC/MS/MS approaches and technologies to assess compound integrity and biotransformation by automation and multiplexing are also discussed. Realization of the benefits in automation of cell-based models for determining drug permeability to predict drug absorption are still hampered by bottlenecks in analytical analysis of compounds. The implementation and limitations of surrogate physiochemical methods for passive adsorption such as immobilized artificial membranes (IAM) and parallel artificial membrane permeation assays (PAMPA), and compound solubility by laser nephelometry are reviewed as well. Additionally, data from a high-throughput 96-well equilibrium dialysis device, showing good correlation to classical methods, is presented. Finally, the impact of improvements in these downstream bottlenecks in lead optimization and preclinical drug discovery are discussed in this review.

Evaluation of ramp control algorithms using microscopic traffic simulation

Ramp metering has emerged as an effective freeway control measure to ensure efficient freeway operations. A number of algorithms have been developed in recent years to ensure an effective use of ramp metering. As the performance of ramp metering depends on various factors (e.g. traffic volume, downstream traffic conditions, queue override policy etc), these algorithms should be evaluated under a wide range of traffic conditions to check their applicability and performance and to ensure their successful implementation. In view of the expenses of and confounding effects in field testing, simulation plays an important role in the evaluation of such algorithms. This paper presents an evaluation study of two ramp metering algorithms: ALINEA and FLOW. ALINEA is a local control algorithm and FLOW is an area wide coordinated algorithm. The purpose of the study is to use microscopic simulation to evaluate systematically how the level of traffic demand, queue spillback handling policy and downstream bottleneck conditions affect the performance of the algorithms. It is believed that these variables have complex interactions with ramp metering. MITSIM microscopic traffic simulator is used to perform the empirical study. The study consists of two stages. In the first stage, key input parameters for the algorithms were identified and calibrated. The calibrated parameters were then used for the second stage, where the performance of the algorithms were compared with respect to three traffic variables mentioned above using an orthogonal fraction of experiments. Regression analysis was used to identify the impacts of some of the interactions among experimental factors on the algorithms' performance, which is not otherwise possible with a tabular analysis. These results provide insights which may be helpful for design and calibration of more efficient ramp control algorithms.

Traffic Congestion at a Two-Tandem Bottleneck

Equilibrium queuing patterns are analyzed in the context of a two-tandem bottleneck with two origins and one destination. The individual in the model chooses his/her departure time, considering the trade-off between travel time and schedule delay. At equilibrium, no one can alter his/her departure time in the sense of the Wardrop principle. Four different configurations are analyzed associated with the capacities of the upstream and the downstream bottlenecks and queuing start times at both bottlenecks. Queuing patterns are determined in the model. It is found that, in some cases, a queue does not occur at the upstream since the departure rate is always equal to its capacity level at equilibrium. Therefore, in order to avoid traffic congestion at a two-tandem bottleneck, the downstream should be enlarged prior to the upstream.

Systemwide Analysis of Freeway Improvements

Determining where to restripe or widen freeway sections to strategically relieve bottlenecks is a far more complicated problem than simply estimating the local capacity effects of specific lane additions. The pros and cons of reducing lane and shoulder widths to obtain an extra travel lane are discussed, with an emphasis on the effects on the overall freeway system. This study describes how increasing capacity at an upstream location can overload a downstream bottleneck and cause flow breakdown. An evaluation of potential local improvements at a number of existing bottlenecks in the westbound Highway 401 corridor in Toronto is provided; it finds that in a systems context about one-half are worthwhile, and the others have net negative effects.

Systemwide Analysis of Freeway Improvements

Determining where to restripe or widen freeway sections to strategically relieve bottlenecks is a far more complicated problem than simply estimating the local capacity effects of specific lane additions. The pros and cons of reducing lane and shoulder widths to obtain an extra travel lane are discussed, with an emphasis on the effects on the overall freeway system. This study describes how increasing capacity at an upstream location can overload a downstream bottleneck and cause flow breakdown. An evaluation of potential local improvements at a number of existing bottlenecks in the westbound Highway 401 corridor in Toronto is provided; it finds that in a systems context about one-half are worthwhile, and the others have net negative effects.

Equilibrium Queueing Patterns at a Two-Tandem Bottleneck during the Morning Peak

Several researchers have analyzed queueing patterns at bottleneck sites on freeways during the morning peak. However, all previous studies have assumed that each commuter passes only one bottleneck during his commuting trip. Here, we consider the possibility that some commuters pass two bottlenecks on their way to work. The objective is to obtain cumulative arrival curves at each of the two bottlenecks, given who passes both bottlenecks and who passes only one, and their desired arrival times at their work places (work starting times). Each commuter using the freeway is assumed to have the same travel cost function which consists of time-dependent costs due to queueing delay (waiting time in a queue) and schedule delay (the time difference between his actual and desired arrival time at the work place). Commuter trips are assigned temporally so as to establish an equilibrium in which each commuter seeks to minimize his travel cost. The queue evolutions illustrate a service priority at the downstream bottleneck in favor of commuters passing only the downstream bottleneck. One of the countermeasures for this equity problem in the service priority would be to meter the favored commuters.

Traffic dynamics

Previous descriptions of traffic flow under changing conditions are shown to be untenable. Deterministic relationships between traffic speed and density do not allow for observed scatter and imply that traffic can lock up spontaneously. Equilibrium relationships between speed and density allow impossibly high traffic densities and provide unrealistically slow responses to changes in roadway and traffic conditions. A qualitatively superior representation of traffic flow is developed. Traffic is described as a fluid that cannot be compressed beyond a certain density, k jam. The equations of state are: (1) Volume = speed x density. (2) Continuity of vehicles. (3) Traffic speed “relaxes” to the free-flow speed of the roadway, independent of density except that volume cannot exceed roadway capacity and flow is incompressible when traffic density is equal to the jam density. The representation is innovative in two respects: (1) Traffic flowing with density = k jam is explicitly recognized as being incompressible. (2) No speed-density relationship is contained in or implied by the traffic formulation. The new traffic formulation models both interrupted and uninterrupted traffic flow. It has been tested by simulating several traffic flow situations. The reproductions of light to moderate flows are equal to those of the best previous traffic formulation, and the representations of congested and bottleneck flow are superior. The new traffic formulation also reproduces the general qualities of observed speed/ volume curves and provides interpretation of those curves in terms of upstream and downstream bottlenecks.

A dynamic model of peak period traffic flows and delays in a corridor

This paper develops and analyses a dynamic model of peak period traffic flows and delays in a congested urban corridor. The model consists of a continous traffic flow model and a probabilistic travel demand model of the choice of departure time. Analytical solution is obtained for the model under no congestion and numerical simulations are used to investigate the general case with congestion. The results demonstrate the interdependencies among upstream and downstream bottlenecks and the interactions among the traffic from different origins.

The Oversaturated Signalized Intersection—Some Statistics

This paper describes the examination of an oversaturated signalized intersection with no turning permitted. During the green phase, data on the time between arrivals of successive vehicles at an intersection with no downstream bottleneck have been collected and analyzed. Measurements were made of only the vehicles in queue, i.e., vehicles that were stopped during the red phase and those that were stopped during the green phase because the starting wave had not traveled back far enough. Measurements were made only on weekdays from approximately 7:00 a.m. to 8:45 a.m. in order to restrict the sample, as far as possible, to commuters. It is shown that shifted Erlang density functions fit the data satisfactorily and that all vehicles from the third on may be considered as members of the same population with different means. The mean arrival times decrease from front to rear with all from the seventh on being the same. In addition, our statistical analysis leads us to accept the hypothesis that all interarrival times are independent. Experimental techniques and statistical methods are described. Two uses of these results are (1) to provide information for Monte Carlo simulations of traffic phenomena in which oversaturated situations are being considered, and (2) to develop, as will be done in a subsequent paper, a renewal model that takes account of variability in the empyting process, and that may be used in formulating control policies for the oversaturated situation.