Three-phase traffic theory
Three-phase traffic theory is a theory of traffic flow developed by Boris Kerner between 1996 and 2002. It focuses mainly on the explanation of the physics of traffic breakdown, Kerner describes three phases of traffic, while the classical theories based on the fundamental diagram of traffic flow have two phases, free flow and congested traffic. A phase is defined as a state in space and time, in free traffic flow, empirical data show a positive correlation between the flow rate q and vehicle density k. This relationship stops at the free flow q max with a corresponding critical density k crit. Data show a relationship between flow and density in congested conditions. Therefore, Kerner argues that the diagram, as used in classical traffic theory. He instead divides congestion into synchronized flow and wide moving jams, in congested traffic, the vehicle speed is lower than the lowest vehicle speed v free min encountered in free flow, i. e. In Kerners theory, the phases J and S in congested traffic are observed outcomes in universal spatial-temporal features of traffic data.
The phases J and S are defined through the definitions and as follows, while doing so, the mean velocity of the downstream front v g is maintained. This is the feature of the wide moving jam that defines the phase J. The phrase moving jam reflects the jam propagation as a whole localized structure on a road, to distinguish wide moving jams from other moving jams, which do not characteristically maintain the mean velocity of the downstream jam front, Kerner used the term wide. Thus the term wide has nothing to do with the width across the jam, in synchronized flow, the downstream front, where the vehicles accelerate to free flow, does not show this characteristic feature of the wide moving jam. Specifically, the front of synchronized flow is often fixed at a bottleneck. The term synchronized flow is meant to reflect the features of this traffic phase, It is a continuous traffic flow with no significant stoppage. The term flow reflects this feature, there is a tendency towards synchronization of vehicle speeds across different lanes on a multilane road in this flow.
In addition, there is a tendency towards synchronization of vehicle speeds in each of the lanes in synchronized flow. This is due to a low probability of passing. The term synchronized reflects this speed synchronization effect, measured data of averaged vehicle speeds illustrate the phase definitions and
The Panama Canal is an artificial 48-mile waterway in Panama that connects the Atlantic Ocean with the Pacific Ocean. The canal cuts across the Isthmus of Panama and is a key conduit for maritime trade. The original locks are 33.5 metres wide, a third, wider lane of locks was constructed between September 2007 and May 2016. The expanded canal began operation on June 26,2016. The new locks allow transit of larger, Post-Panamax ships, capable of handling more cargo, France began work on the canal in 1881 but stopped due to engineering problems and a high worker mortality rate. The United States took over the project in 1904 and opened the canal on August 15,1914, Colombia and the United States controlled the territory surrounding the canal during construction. The U. S. continued to control the canal and surrounding Panama Canal Zone until the 1977 Torrijos–Carter Treaties provided for handover to Panama. After a period of joint American–Panamanian control, in 1999 the canal was taken over by the Panamanian government and is now managed and operated by the government-owned Panama Canal Authority.
Annual traffic has risen from about 1,000 ships in 1914, by 2012, more than 815,000 vessels had passed through the canal. It takes six to eight hours to pass through the Panama Canal, the American Society of Civil Engineers has called the Panama Canal one of the seven wonders of the modern world. Such a route would have given the Spanish a military advantage over the Portuguese, during an expedition from 1788 to 1793, Alessandro Malaspina outlined plans for its construction. Given the strategic location of Panama and the potential offered by its narrow isthmus separating two great oceans, other links in the area were attempted over the years. The ill-fated Darien scheme was launched by the Kingdom of Scotland in 1698 to set up a trade route. Generally inhospitable conditions thwarted the effort, and it was abandoned in April 1700, another effort was made in 1843. They referred to it as the Atlantic and Pacific Canal and it was a wholly British endeavor and it was expected to be completed in five years, but the plan was never carried out.
At nearly the same time, other ideas were floated, including a canal across Mexicos Isthmus of Tehuantepec. Nothing came of that plan either. )In 1846 the Mallarino–Bidlack Treaty, negotiated between the U. S. and New Granada, granted the United States transit rights and the right to intervene militarily in the isthmus. In 1849, the discovery of gold in California created great interest in a crossing between the Atlantic and Pacific Oceans, the Panama Railway was built by the United States to cross the isthmus and opened in 1855
A choke point can allow a numerically inferior defending force to thwart a larger opponent if the attacker cannot bring superior numbers to bear. It was the suitability of the Caribbean as a chokepoint that attracted pirates, the Spanish treasure fleets leaving the Americas would need to pass there to pick up the strong, westerly winds that would take them back to Spain. From the 18th to the early 20th centuries, the size of the United Kingdoms Royal Navy meant it had control over much of the worlds oceans. Choke points were of importance to the British Empire, which often used them to control trade in British colonies and, to a lesser extent. Choke points have been a source of tension, notably during the Suez Crisis, the Royal Navy still deems its choke points as strategically vital. Indeed, the importance of choke points was first recognised by British Admiral John Fisher and these are major British choke points today, The English Channel GIUK gap Strait of Gibraltar The choke points still have significant strategic importance for the Royal Navy.
The GIUK gap was a important part of the Cold War. The Suez Canal and the Sumed pipeline carry 4.5 million barrels a day, the canal was closed for eight years after the Six Day War in 1967. In many instances, alternate routes are nonexistent or impractical, for example, an alternate to the Suez/Sumed route required an additional 6,000 miles around Cape of Good Hope. The Royal Navy still deems its choke points to the Atlantic as strategically important, strategic geography Sea lines of communication String of Pearls
The worlds first, manually operated gas-lit traffic signal was short lived. Installed in London in December 1868, it exploded less than a month later, Traffic control started to seem necessary in the late 1890s and Earnest Sirrine from Chicago patented the first automated traffic control system in 1910. It used the words STOP and PROCEED, although neither word lit up, Traffic lights alternate the right of way accorded to users by displaying lights of a standard colour following a universal colour code. In the typical sequence of phases, The green light allows traffic to proceed in the direction denoted, if it is safe to do so. The amber light warns that the signal is about to change to red, in a number of countries – among them the United Kingdom – a phase during which red and yellow are displayed together indicates that the signal is about to change to green. A flashing amber indication is a warning signal, in the United Kingdom, a flashing amber light is used only at pelican crossings, in place of the combined red–amber signal, and indicates that drivers may pass if no pedestrians are on the crossing.
The red signal prohibits any traffic from proceeding, a flashing red indication is treated as a stop sign. In some countries traffic signals will go into a flashing mode if the Conflict Monitor detects a problem, the signal may display flashing yellow to the main road and flashing red to the side road, or flashing red in all directions. Flashing operation can be used during times of day when traffic is light, before traffic lights traffic police controlled the flow of traffic, a well-documented example being that on London Bridge in 1722. Three men were given the task of directing traffic coming in, each officer would help direct traffic coming out of Southwark into London and he made sure all traffic stayed on the west end of the bridge. A second officer would direct traffic on the east end of the bridge to control the flow of people leaving London and going into Southwark. The main reason for the light was that there was an overflow of horse-drawn traffic over Westminster Bridge which forced thousands of pedestrians to walk next to the Houses of Parliament.
The design combined three semaphore arms with red and green gas lamps for use, on a pillar. The gas lantern was manually turned by a police officer. The signal was 22 feet high, at night a red light would command Stop and a green light would mean use Caution. Although it was said to be successful at controlling traffic, its life was brief. It exploded on 2 January 1869, as a result of a leak in one of the gas lines underneath the pavement, injuring or killing the policeman who was operating it. In the first two decades of the 20th century semaphore traffic signals, like the one in London, were in use all over the United States with each state having its own design of the device, One good example was from Toledo, Ohio in 1908
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, Traffic behaves in a complex and nonlinear way, depending on the interactions of a large number of vehicles. Some mathematical models of traffic flow use a vertical queue assumption, in a free-flowing network, traffic flow theory refers to the traffic stream variables of speed and concentration. These relationships are mainly concerned with uninterrupted traffic flow, primarily found on freeways or expressways, Flow conditions are considered free when less than 12 vehicles per mile are on a road. Stable is sometimes described as 12–30 vehicles per mile per lane, as the density reaches the maximum flow rate and exceeds the optimum density, traffic flow becomes unstable, and even a minor incident can result in persistent stop-and-go driving conditions. A breakdown condition occurs when traffic becomes unstable and exceeds 67 vehicles per mile, jam density refers to extreme traffic density when traffic flow stops completely, usually in the range of 185–250 vehicles per mile per lane.
However, calculations about congested networks are complex and rely more on empirical studies. Because these are urban or suburban in nature, other factors influence the optimum conditions. There are common spatiotemporal features of traffic congestion that are qualitatively the same for different highways in different countries. Some of these features of traffic congestion define synchronized flow. Traffic flow is generally constrained along a one-dimensional pathway, a time-space diagram shows graphically the flow of vehicles along a pathway over time. Time is displayed along the axis, and distance is shown along the vertical axis. Traffic flow in a diagram is represented by the individual trajectory lines of individual vehicles. Vehicles following each other along a given travel lane will have parallel trajectories, time-space diagrams are useful tools for displaying and analyzing the traffic flow characteristics of a given roadway segment over time. There are three variables to visualize a traffic stream, speed and flow.
Speed is the distance covered per unit time, one cannot track the speed of every vehicle, so, in practice, average speed is measured by sampling vehicles in a given area over a period of time. Two definitions of average speed are identified, time mean speed, time mean speed is measured at a reference point on the roadway over a period of time. In practice, it is measured by the use of loop detectors, loop detectors, when spread over a reference area, can identify each vehicle and can track its speed
International Standard Serial Number
An International Standard Serial Number is an eight-digit serial number used to uniquely identify a serial publication. The ISSN is especially helpful in distinguishing between serials with the same title, ISSN are used in ordering, interlibrary loans, and other practices in connection with serial literature. The ISSN system was first drafted as an International Organization for Standardization international standard in 1971, ISO subcommittee TC 46/SC9 is responsible for maintaining the standard. When a serial with the content is published in more than one media type. For example, many serials are published both in print and electronic media, the ISSN system refers to these types as print ISSN and electronic ISSN, respectively. The format of the ISSN is an eight digit code, divided by a hyphen into two four-digit numbers, as an integer number, it can be represented by the first seven digits. The last code digit, which may be 0-9 or an X, is a check digit. Formally, the form of the ISSN code can be expressed as follows, NNNN-NNNC where N is in the set, a digit character.
The ISSN of the journal Hearing Research, for example, is 0378-5955, where the final 5 is the check digit, for calculations, an upper case X in the check digit position indicates a check digit of 10. To confirm the check digit, calculate the sum of all eight digits of the ISSN multiplied by its position in the number, the modulus 11 of the sum must be 0. There is an online ISSN checker that can validate an ISSN, ISSN codes are assigned by a network of ISSN National Centres, usually located at national libraries and coordinated by the ISSN International Centre based in Paris. The International Centre is an organization created in 1974 through an agreement between UNESCO and the French government. The International Centre maintains a database of all ISSNs assigned worldwide, at the end of 2016, the ISSN Register contained records for 1,943,572 items. ISSN and ISBN codes are similar in concept, where ISBNs are assigned to individual books, an ISBN might be assigned for particular issues of a serial, in addition to the ISSN code for the serial as a whole.
An ISSN, unlike the ISBN code, is an identifier associated with a serial title. For this reason a new ISSN is assigned to a serial each time it undergoes a major title change, separate ISSNs are needed for serials in different media. Thus, the print and electronic versions of a serial need separate ISSNs. Also, a CD-ROM version and a web version of a serial require different ISSNs since two different media are involved, the same ISSN can be used for different file formats of the same online serial
Many wider U. S. as well as Swedish freeways have shoulders on both sides of each directional carriageway, in the median as well as at the outer edges of the road, for additional safety. Shoulders are not intended for use by traffic, although there are exceptions. Shoulders have multiple uses, including, In the event of an emergency or breakdown, Emergency vehicles such as ambulances and police cars may use the shoulder to bypass traffic congestion. Active traffic management, used on busy roads, may allow hard shoulder running by general traffic at reduced speeds during periods of high traffic volumes. In some places a Bus bypass shoulder may be provided which allows bus services to pass stationary traffic, paved shoulders provide additional space should a motorist need to take evasive action or need to recover control of their vehicle before a run-off-road collision occurs. In some urban areas, shoulders are used as travel lanes during peak commuting hours, in some rural areas without sidewalks and cyclists may be allowed to walk or ride on the shoulders.
Paved shoulders move water away from the roadway before it can infiltrate into the roads subbase, Shoulders help provide extra structural support of the roadway. The shoulder is slightly narrower than a full traffic lane. In some cases, particularly on older rural roadways, shoulders that initially existed were hardened with gravel rather than being paved with asphalt or concrete, in Britain, motorway shoulders are now paved, but are still known as hard shoulders. Older, gravel shoulders have sometimes been termed soft shoulders by comparison, because the paved surface ends at that point, they are less safe if they need to be used for emergency maneuvers. Modern practice is to build a paved shoulder whenever possible. The Safety Edge is effective on roads where the shoulder is narrow or nonexistent. To save money, the shoulder was not paved to the same thickness as the through lanes, so if vehicles were to attempt to use it as a through lane regularly. In Britain, shoulder running can occur during roadworks, and full depth construction is now standard, in some metro areas, road authorities allow shoulders to be used as lanes at peak periods.
However, rural shoulders often collects various bits of debris that can make driving there less safe. Drivers will sometimes drift into the shoulder when being overtaken by passing vehicles, however, it is extremely unsafe, as well as illegal, to abuse the shoulder by undertaking passing vehicles that are nearer the center of the road. Some roads have a shoulder for significant distances. This makes it difficult for vehicles to pull into the hard shoulder altogether
Traffic congestion is a condition on transport networks that occurs as use increases, and is characterized by slower speeds, longer trip times, and increased vehicular queueing. The most common example is the use of roads by vehicles. When traffic demand is great enough that the interaction between vehicles slows the speed of the stream, this results in some congestion. As demand approaches the capacity of a road, extreme traffic congestion sets in, when vehicles are fully stopped for periods of time, this is colloquially known as a traffic jam or traffic snarl-up. Traffic congestion can lead to becoming frustrated and engaging in road rage. Mathematically, congestion is usually looked at as the number of vehicles that pass through a point in a window of time, Congestion flow lends itself to principles of fluid dynamics. Traffic congestion occurs when a volume of traffic or modal split generates demand for greater than the available street capacity. About half of U. S. traffic congestion is recurring, Traffic research still cannot fully predict under which conditions a traffic jam may suddenly occur.
It has been found that individual incidents may cause ripple effects which spread out and create a traffic jam when, otherwise. Some traffic engineers have attempted to apply the rules of fluid dynamics to traffic flow, Traffic scientists liken such a situation to the sudden freezing of supercooled fluid. However, unlike a fluid, traffic flow is affected by signals or other events at junctions that periodically affect the smooth flow of traffic. Alternative mathematical theories exist, such as Boris Kerners three-phase traffic theory, because of the poor correlation of theoretical models to actual observed traffic flows, transportation planners and highway engineers attempt to forecast traffic flow using empirical models. These models are typically calibrated by measuring actual traffic flows on the links in the network. That discovery enabled the team to solve traffic-jam equations that were first theorized in the 1950s, congested roads can be seen as an example of the tragedy of the commons.
Privatization of highways and road pricing have both proposed as measures that may reduce congestion through economic incentives and disincentives. Congestion can happen due to non-recurring highway incidents, such as a crash or roadworks, economist Anthony Downs argues that rush hour traffic congestion is inevitable because of the benefits of having a relatively standard work day. In a capitalist economy, goods can be allocated either by pricing or by queueing and they determined that the number of vehicle-kilometers traveled increases in direct proportion to the available lane-kilometers of roadways. The implication is that new roads and widening existing ones only results in additional traffic that continues to rise until peak congestion returns to the previous level