|
Fundamental Diagram Of Traffic Flow
The fundamental diagram of traffic flow is a diagram that gives a relation between road traffic flux (vehicles/hour) and the traffic density (vehicles/km). A macroscopic traffic model involving traffic flux, traffic density and velocity forms the basis of the fundamental diagram. It can be used to predict the capability of a road system, or its behaviour when applying inflow regulation or speed limits. Basic statements * There is a connection between traffic density and vehicle velocity: The more vehicles are on a road, the slower their velocity will be. * To prevent congestion and to keep traffic flow stable, the number of vehicles entering the control zone has to be smaller or equal to the number of vehicles leaving the zone in the same time. * At a critical traffic density and a corresponding critical velocity the state of flow will change from stable to unstable. * If one of the vehicles brakes in unstable flow regime the flow will collapse. The primary tool for graphically ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diagram
A diagram is a symbolic representation of information using visualization techniques. Diagrams have been used since prehistoric times on walls of caves, but became more prevalent during the Enlightenment. Sometimes, the technique uses a three-dimensional visualization which is then projected onto a two-dimensional surface. The word '' graph'' is sometimes used as a synonym for diagram. Overview The term "diagram" in its commonly used sense can have a general or specific meaning: * ''visual information device'' : Like the term " illustration", "diagram" is used as a collective term standing for the whole class of technical genres, including graphs, technical drawings and tables. * ''specific kind of visual display'' : This is the genre that shows qualitative data with shapes that are connected by lines, arrows, or other visual links. In science the term is used in both ways. For example, Anderson (1997) stated more generally: "diagrams are pictorial, yet abstract, repres ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Speed Limit
Speed limits on road traffic, as used in most countries, set the legal maximum speed at which vehicles may travel on a given stretch of road. Speed limits are generally indicated on a traffic sign reflecting the maximum permitted speed - expressed as kilometres per hour (km/h) and/or miles per hour (mph). Speed limits are commonly set by the legislative bodies of national or provincial governments and enforced by national or regional police and judicial authorities. Speed limits may also be variable, or in some places nonexistent, such as on most of the Autobahnen in Germany. The first numeric speed limit for automobiles was the limit introduced in the United Kingdom in 1861. the highest posted speed limit in the world is , applied on two motorways in the UAE. Speed limits and safety distance are poorly enforced in the UAE, specifically on the Abu Dhabi to Dubai motorway - which results in dangerous traffic, according to a French-government travel-advisory. Additionally, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fundamental Diagram
The fundamental diagram of traffic flow is a diagram that gives a relation between road traffic flux (vehicles/hour) and the traffic density (vehicles/km). A macroscopic traffic model involving traffic flux, traffic density and velocity forms the basis of the fundamental diagram. It can be used to predict the capability of a road system, or its behaviour when applying inflow regulation or speed limits. Basic statements * There is a connection between traffic density and vehicle velocity: The more vehicles are on a road, the slower their velocity will be. * To prevent congestion and to keep traffic flow stable, the number of vehicles entering the control zone has to be smaller or equal to the number of vehicles leaving the zone in the same time. * At a critical traffic density and a corresponding critical velocity the state of flow will change from stable to unstable. * If one of the vehicles brakes in unstable flow regime the flow will collapse. The primary tool for graphically ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sample Traffic Flow Macroscopic Fundamental Diagram
Sample or samples may refer to: Base meaning * Sample (statistics), a subset of a population – complete data set * Sample (signal), a digital discrete sample of a continuous analog signal * Sample (material), a specimen or small quantity of something * Sample (graphics), an intersection of a color channel and a pixel * SAMPLE history, a mnemonic acronym for questions medical first responders should ask * Product sample, a sample of a consumer product that is given to the consumer so that he or she may try a product before committing to a purchase * Standard cross-cultural sample, a sample of 186 cultures, used by scholars engaged in cross-cultural studies People *Sample (surname) *Samples (surname) * Junior Samples (1926–1983), American comedian Places * Sample, Kentucky, unincorporated community, United States * Sampleville, Ohio, unincorporated community, United States * Hugh W. and Sarah Sample House, listed on the National Register of Historic Places in Iowa, United ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Time Space Diag Figure 2
Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to compare the duration of events or the intervals between them, and to quantify rates of change of quantities in material reality or in the conscious experience. Time is often referred to as a fourth dimension, along with three spatial dimensions. Time has long been an important subject of study in religion, philosophy, and science, but defining it in a manner applicable to all fields without circularity has consistently eluded scholars. Nevertheless, diverse fields such as business, industry, sports, the sciences, and the performing arts all incorporate some notion of time into their respective measuring systems. 108 pages. Time in physics is operationally defined as "what a clock reads". The physical nature of time is address ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Congestion Pricing
Congestion pricing or congestion charges is a system of surcharging users of public goods that are subject to congestion through excess demand, such as through higher peak charges for use of bus services, electricity, metros, railways, telephones, and road pricing to reduce traffic congestion; airlines and shipping companies may be charged higher fees for slots at airports and through canals at busy times. Advocates claim this pricing strategy regulates demand, making it possible to manage congestion without increasing supply. According to the economic theory behind congestion pricing, the objective of this policy is the use of the price mechanism to make users conscious of the costs that they impose upon one another when consuming during the peak demand, and that they should pay for the additional congestion they create, thus encouraging the redistribution of the demand in space or in time, and forcing them to pay for the negative externalities they create, making users mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Saturation (traffic)
In traffic engineering, saturation describes the maximum traffic flow which can be handled by a junction. The saturation flow is the rate at which a continuous flow of vehicles can pass through a constant green signal, typically expressed in vehicles per hour or PCUs per hour. A formula to calculate saturation flows based on lane geometry is given in Transport and Road Research Laboratory RR67. However, the formula can over-estimate saturation flows at congested locations. Degree of Saturation The degree of saturation (DoS) of an intersection (typically under traffic signal Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at road intersections, pedestrian crossings, and other locations in order to control flows of traffic. Traffic lights ... control) or a link measures the demand relative to the total capacity. A DoS value of 100% meaning that demand and capacity are equal and no further traffic is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Smith Predictor
The Smith predictor (invented by O. J. M. Smith in 1957) is a type of predictive controller designed to control systems with a significant feedback time delay. The idea can be illustrated as follows. Suppose the plant consists of G(z) followed by a pure time delay z^. z refers to the Z-transform of the transfer function relating the inputs and outputs of the plant G. As a first step, suppose we only consider G(z) (the plant without a delay) and design a controller C(z) with a closed-loop transfer function H(z)=\frac that we consider satisfactory. Next, our objective is to design a controller \bar(z) for the plant G(z) z^ so that the closed loop transfer function \bar(z) equals H(z) z^. Solving \frac = z^ \frac, we obtain \bar = \frac. The controller is implemented as shown in the following figure, where G(z) has been changed to \hat(z) to indicate that it is a model used by the controller. Note that there are two feedback loops. The outer control loop feeds the output back ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Control Engineering
Control engineering or control systems engineering is an engineering discipline that deals with control systems, applying control theory to design equipment and systems with desired behaviors in control environments. The discipline of controls overlaps and is usually taught along with electrical engineering and mechanical engineering at many institutions around the world. The practice uses sensors and detectors to measure the output performance of the process being controlled; these measurements are used to provide corrective feedback helping to achieve the desired performance. Systems designed to perform without requiring human input are called automatic control systems (such as cruise control for regulating the speed of a car). Multi-disciplinary in nature, control systems engineering activities focus on implementation of control systems mainly derived by mathematical modeling of a diverse range of systems. Overview Modern day control engineering is a relatively new field o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PI Controller
A proportional–integral–derivative controller (PID controller or three-term controller) is a control loop mechanism employing feedback that is widely used in industrial control systems and a variety of other applications requiring continuously modulated control. A PID controller continuously calculates an ''error value'' e(t) as the difference between a desired setpoint (SP) and a measured process variable (PV) and applies a correction based on proportional, integral, and derivative terms (denoted ''P'', ''I'', and ''D'' respectively), hence the name. In practical terms, PID automatically applies an accurate and responsive correction to a control function. An everyday example is the cruise control on a car, where ascending a hill would lower speed if constant engine power were applied. The controller's PID algorithm restores the measured speed to the desired speed with minimal delay and overshoot by increasing the power output of the engine in a controlled manner. The first ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Traffic Flow
In mathematics and transportation engineering, traffic flow is the study of interactions between travellers (including pedestrians, cyclists, drivers, and their vehicles) and infrastructure (including highways, signage, and traffic control devices), with the aim of understanding and developing an optimal transport network with efficient movement of traffic and minimal traffic congestion problems. History Attempts to produce a mathematical theory of traffic flow date back to the 1920s, when Frank Knight first produced an analysis of traffic equilibrium, which was refined into Wardrop's first and second principles of equilibrium in 1952. Nonetheless, even with the advent of significant computer processing power, to date there has been no satisfactory general theory that can be consistently applied to real flow conditions. Current traffic models use a mixture of empirical and theoretical techniques. These models are then developed into traffic forecasts, and take account of p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Traffic Wave
Traffic waves, also called stop waves, ghost jams, traffic snakes or traffic shocks, are traveling disturbances in the distribution of cars on a highway. Traffic waves travel backwards relative to the cars themselves. Relative to a fixed spot on the road the wave can move with, or against the traffic, or even be stationary (when the wave moves away from the traffic with exactly the same speed as the traffic). Traffic waves are a type of traffic jam. A deeper understanding of traffic waves is a goal of the physical study of traffic flow, in which traffic itself can often be seen using techniques similar to those used in fluid dynamics. It is related to the accordion effect. Mitigation It has been saidTraffic Wave Experiments William J. Beaty, 1998 that by knowing how traffic waves are created, drivers can sometimes reduce their effect ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
