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Amy Sumler
Providing the player with new tools or adjusting the game interface, without fundamentally changing gameplay. 3 years ago 0.13 - 1.1 198K source code Download
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Only the first and second sources contribute to recurring congestion; i.e., they are tangible in design and function, and therefore, candidates for remediation. The remaining sources of congestion are nonrecurring and random. In this context then, a bottleneck certainly constitutes "congestion," but congestion cannot be said to be universally analogous to a "bottleneck". In much the same way that "paper" can be used to describe either a singular sheet or multiple sheets, "congestion" can be meant to describe the result of a local circumstance or an overarching systemic condition. It is not merely sufficient to explain that "high volumes" represent congestion, for this is a term that is relatively applied. High volumes, or at least higher volumes than designed for a facility, including even higher than the design volume plus a safety factor, will overburden any facility, regardless of whether operational influences exist or not. When too many vehicles compete along all segments of a facility, "congestion" will inevitably result, and is overarching. But when only determinant, subordinate segments of that facility are routinely over taxed, then "operationally recurring bottlenecks" within the facility are said to exist.
Among Webster's dictionary definitions of "bottleneck" are i) a narrow or obstructed portion of a highway or pipeline, and ii) a hindrance to production or progress. Certainly the elemental roots of a traffic bottleneck exist in these descriptions; namely, the narrow portion of highway and the hindrance to progress. However, a road need not "narrow" for a recurring bottleneck condition to result: e.g., witness a weave condition, sun glare, or a vertical climb. For that reason and others, in the context of traffic analysis, there are recurring and nonrecurring causes of bottlenecks, which invariably shapes one's definition. Note: across all FHWA sites "bottleneck" is often used interchangeably and idly as a catch-all definition including sometimes even meaning "congestion." One should recognize the context, and distinguish it appropriately as a "recurring" or "nonrecurring" bottleneck. Specific to this site, the reader is reminded that the LBR Program is dedicated to operationally influenced recurring bottlenecks.
In layman's terms, a bottleneck is distinguished from "congestion" because it occurs on a subordinate segment of a parent facility, and not pervasively along the entire facility. It is mandatory only for recurring bottlenecks that "traffic over-demand" be present. "Rubbernecking" past traffic incidents that do not require a lane closure, or simply driving into sun glare, often results in slowdowns even though excess traffic demand may not be present. The mere act of one or more lead vehicles slowing creates a rippling effect; a shock wave that reverberates back to vehicles that are following. In other words, this slowing could be the result of a traffic confluence or the rubbernecking. The slowing reduces room to maneuver, which self-perpetuates the shock wave. The problem begins to clear once past the incident, as vehicles begin to accelerate away, and maneuvering room downstream of the incident increases. One California study found that the mere optical illusion of a bridge that appears lower than it really is creates a recurring bottleneck on Interstate 880 north approaching 23rd Avenue. Truckers slow in anticipation of the "low" bridge, thereby forcing following vehicles to adjust. The location is independent of a classic operational deficiency and can be independent of volume. Nevertheless, the condition creates a bottleneck.
Good question! The FHWA Office of Freight Management and Operations is tasked with understanding the challenges that come with the increasing demand for freight transportation, and improving freight mobility and productivity. Understanding "freight bottlenecks" is a specialized study within that program area. Freight bottlenecks are both unique to this genre (e.g., steep upgrades, truck operating restrictions or limitations, delays at terminals) but also routine (e.g., stuck in traffic at notorious backups) in that they contribute to higher pass-through costs of goods. Therefore, a freight bottleneck is "freight stuck in traffic" but more to the point, the study of the economic loss of those goods being stuck in traffic. Getting freight moving around or through bottlenecks on trucking routes is a focus of that program. One might argue there is little difference in freight or any other user caught in a bottleneck; free up the bottleneck and everyone benefits. But highway service holds such great import to the trucking industry that "freight analysis" is justified as a unique area of study by the FHWA and peer organizations. Whereas, the LBR Program focuses on localized, operationally influenced bottlenecks, the Freight Analysis program focuses on major freight routes and the impact to the economy. If solving an LBR Program "bottleneck" includes solving a major freight-impacting location, all the better.
The LBR Program focuses on operationally influenced locations; that is to say, those that have an identifiable cause, resulting in recurring delays of generally predictable times and durations. The root cause of traffic flow degradation at the subject point of constriction is a potentially correctable solution. The following conditions either exist or help to identify a recurring bottleneck condition.
The first step in bottleneck remediation is identifying bottleneck locations and the root causes of the bottleneck. Sometimes, the problem is evident, intuitive, or anecdotal. However, within multi-mile corridor congestion, travel demand models can assist in Identifying, separating, and analyzing bottleneck dynamics within the corridor. Traffic analysis tools can mathematically identify the problem areas by analyzing road segments for congestion or poor levels of service. Freeways with traffic detection use archived data to identify where and how often bottlenecks occur, and how severe they are. Historical data is used to determine if the problem is growing or receding.
Determining the root cause of the bottleneck can be accomplished with a range of tools. Travel-time runs and videos of problem areas can be used to pinpoint and measure deficiencies. Micro simulation tools can provide a detailed analysis of the specific attributes of the bottleneck(s) and can assist in determining the impact of alternative solutions. When conducting bottleneck analysis, care should be taken to ensure that:
Here is a sampling of remediations that would apply to low-cost, quick-fix, operationally influenced bottlenecks. (Note: other solutions not mentioned here might exist for larger bottlenecks or systemic corridor congestion.)
In a 2006 survey of state and local agencies, the most frequently mentioned operational bottleneck improvements were ramp metering, auxiliary lanes, and introduction of high occupancy vehicle (HOV) lanes. To what degree these are "low-cost" is for the agency to decide. Certainly, other remediations may serve other bottleneck problem areas.
The knee jerk reaction might be "lack of money." But that's everyone's first complaint about, well, most every problem! In visiting with many states to ascertain if they have a bottleneck-specific program or similar that targets chokepoint congestion, we have found a sampling of reasons.
Conversely, recurring congestion has been described as repeating and predictable events, as typically exemplified by routine commuter peak hour backups. For the most part, contributing operational designs like lane drops, merging or diverging at on- and off-ramps, too-short turn lanes and ramps (that, for instance, cause back up congestion onto the mainline), traffic signal delays, and weaving sections take the brunt of the blame. Remove the overburden and the congestion dissipates; which is to say that at "off" times when the overburden doesn't exist, the operational element is unobtrusively innocent. (If the operational design is inherently unsafe it would require attention on that merit). Whether or not this recurring congestion is locally determinant (i.e., bottlenecks and chokepoints) or systemic (overarching due to a vehicle-dense urban area) is less the issue than are the predictable, resulting slowdowns themselves. To paraphrase a favorite observation of anyone stuck in traffic: "I'm not the problem! The rest of you are!"
The inverse arguments are that motorists see these exogenous conditions regularly and should inure themselves to face them as part of everyday motoring. Put another way, these are background conditions that are wholly static and undeserving of blame. Or are they? Can this list of exogenous factors actually be acted upon such that improved lane definition, improved shoulder definition, improved pavement friction and improved night-driving conditions (e.g., streetlights) combine to reduce congestion? Would transportation agencies be willing or able to afford to undertake "corrections" or improvements to hundreds (thousands? millions?) of lane-miles of mostly innocuous parameters on such a scale that it would justify benefiting any resulting congestion reduction? Or should we continue our efforts on the known "thumbprint" locations of operationally induced local bottlenecks and chokepoints that would seem to have a higher benefit/cost return?
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