Characteristics of speed dispersion and its relationship to fundamental traffic flow parameters

[[abstract]]Speed dispersion is essential for transportation research but inaccessible to certain sensors that simply record density, mean speed, and/or flow. An alternative is to relate speed dispersion with these available parameters. This paper is compiled from nearly a quarter million observations on an urban freeway and a resulting data-set with two speed dispersion measures and the three fundamental parameters. Data are examined individually by lane and aggregately by direction. The first dispersion measure, coefficient of variation of speed, is found to be exponential with density, negative exponential with mean speed, and two-phase linear to flow. These empirical relationships are proven to be general for a variety of coefficient ranges under the above function forms. The second measure, standard deviation of speed, does not present any simple relationships to the fundamental parameters, and its maximum occurs at around a half to two-thirds of the free flow speed. Speed dispersion may be significantly different by lane.[[notice]]補正完畢[[journaltype]]國外[[incitationindex]]SCI[[incitationindex]]EI[[ispeerreviewed]]Y[[booktype]]紙本[[booktype]]電子版[[countrycodes]]GB

Operational Assessment of Speed Priority for High-Occupancy Vehicle Lanes over General-Purpose Lanes

[[abstract]]Current guidelines arguably do not properly address how much high-occupancy vehicle (HOV) lanes should be prioritized over general-purpose (GP) lanes. This study develops two schemes for HOV and GP lanes by utilizing the concept of “speed equilibrium,” which determines whether HOV lanes are under-prioritized, over-prioritized, or well-prioritized. The first scheme incorporates average vehicle occupancy with speed priorities, reflecting the HOV core value of carrying more persons in fewer vehicles; HOV lanes maintain higher equilibrium speeds than GP lanes, but the differences decrease as traffic speeds decrease from free flow to jam states. The second scheme is a revision of the existing HOV principle: equilibrium built upon the principle of time saved leads to increasingly greater HOV speeds relative to GP lane speeds, as traffic volumes increase. Both schemes are visualized in three-dimensional data plots to illustrate the effects of individual traffic variables. Using only a single measure, i.e., speed, ensures inferior HOV priority with respect to mobility and reliability. Observed freeway data were applied to the two schemes, and the results can be used to determine the necessity of HOV policy adjustment. The schemes are complimentary to current HOV operational assessments.[[sponsorship]]Transportation Research Board[[conferencetype]]國際[[conferencedate]]20140112~20140116[[booktype]]電子版[[iscallforpapers]]Y[[conferencelocation]]Washington D.C., U.S.A

A Review and Advance of High-Occupancy Toll Lanes’ Toll Schemes

[[abstract]]This paper reviews the pricing of high-occupancy toll (HOT) lanes and finds that 1) existing dynamic pricing adjusts every 3-15 minutes according to such parameters as speed, density, and/or volume, 2) tolls increase progressively with traffic to ensure free flow HOT lanes, 3) for multi-zone HOT lanes, tolls tend to be determined by the most congested zone, 4) the reaction of motorists to toll adjustments is either unspecified or oversimplified, and 5) a toll boundary is essential to mediate extreme fluctuations. Based on values of time savings and reliability, a novel toll scheme was proposed as a function of speed of general-purpose lanes; tolls in a selected 10-mile HOT corridor varied between $0.77 and$12.64 per use, of which the value of reliability accounted for 24% to 44% while that of time savings accounted for the remainder. The proposed toll scheme can be applied to time-of-day or dynamic HOT pricing.[[sponsorship]]Eastern Asia Societies for Transportation Studies[[conferencetype]]國際[[conferencedate]]20130909~20130913[[booktype]]電子版[[iscallforpapers]]Y[[conferencelocation]]Taipei, Taiwa

The Role of Bhlhe40 in Autoimmune Neuroinflammation and Mycobacterial Infection

The mammalian immune system is composed of innate and adaptive compartments, which cooperate with each other to maintain homeostasis and protect the host from the invasion by a variety of pathogens. The tight control of immune responses is extremely important for all individuals. Here, we discovered that the transcription factor basic helix-loop-helix family, member e40 (Bhlhe40) is a critical protein that regulates the autoimmune ( against self ) and anti-microbial ( against non-self ) responses of myeloid cells and T lymphocytes. Multiple sclerosis (MS) is a human neuroinflammatory disease in the central nervous system with an autoimmune etiology. We have reported that Bhlhe40 positively regulates the production of the pro-inflammatory cytokine, GM-CSF, but negatively regulates the production of the anti-inflammatory cytokine, IL-10, by CD4+ T cells. The absence of Bhlhe40 abrogates T cell pathogenicity and thus Bhlhe40-/- mice were resistant to the animal model of MS. Tuberculosis, caused by Mycobacterium tuberculosis (Mtb), is one of the most serious infectious diseases in the world. We have demonstrated that Bhlhe40 suppresses IL-10 expression by myeloid cells and T cells to ensure protective immunity to Mtb. Bhlhe40-deficient immune cells produce high levels of IL-10 which dampens the immune responses to Mtb infection and therefore renders Bhlhe40-/- mice highly susceptible to this pathogen. Our findings have uncovered the critical roles of Bhlhe40 in regulating inflammation during an autoimmune disorder and an infectious disease. Bhlhe40, or pathways that regulate its expression or function, might represent therapeutic targets for researchers to manipulate immune responses in human autoimmunity and infection

Characteristics of Speed Dispersion and Its Relationships with the Fundamental Traffic Flow Parameters in Urban Freeways: A Case Study in Northern California

[[abstract]]This research reveals statistical characteristics of speed dispersion and its relationships with fundamental traffic flow parameters in northern California. Nearly a quarter million vehicle observations of a five-lane urban freeway are examined individually by lane and aggregately for a total of seven categories. Speed dispersion is measured by coefficient of variation of speed (CVS) and standard deviation of speed (SDS). CVS displays an exponential form of occupancy or space mean speed, and is two-phase linear to flow. Variation of CVS is stable and similar across lanes during light traffic, and afterward increases and diverges into three groups. SDS in contrast does not present any simple equation of the fundamental parameters. Both CVS and SDS of the all lane mix are greater than those of other categories given fixed occupancy or mean speed.[[notice]]補正完畢[[conferencetype]]國際[[conferencedate]]20100110~20100114[[ispeerreviewed]]Y[[booktype]]電子版[[iscallforpapers]]Y[[conferencelocation]]Washington D.C., U.S.A.[[countrycodes]]US

KNOWLEDGE SHARING IN VIRTUAL COMMUNITIES: THE ROLE OF GROUP IDENTITY

The rapid growth of network access and the development of Web 2.0 have resulted in the popularity of virtual communities (VCs), such as Wikipedia, Facebook, professional forums and social network communities. The impact of VCs increasingly spreads over a broad range of fields, from social and educational to business. The content (i.e., knowledge) that VC members provide is the factor that determines the growth and survival of VCs. Previous studies have investigated the factors that influence knowledge-sharing behavior in the VC environment. Despite the fact that these studies have examined the same factors, their findings have been inconsistent. In this paper, we argue that group identity mediates the relationships between knowledge sharing and these factors. This study adopts social identity theory as a theoretical foundation and collects data from a popular virtual community in Taiwan. The results show that group identity indeed mediates the relationships between VC member knowledge sharing and both organizational commitment and organizational support