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

Comparative study of spectral and morphological properties of blends of P3HT with PCBM and ICBA

[[abstract]]We report a comparative study on spectral and morphological properties of two blend systems for polymer solar cells: the donor material poly(3-hexylthiophene) (P3HT) in combination with the acceptor material of either [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) or indene-C60 bisadduct (ICBA) that was reported to enhance efficiencies of polymer solar cells. Optical microscopy and grazing incidence X-ray scattering reveal the stronger tendency of PCBM to from larger and more ordered domains/grains than ICBA either in pure or blend films. Compared to PCBM, the presence of ICBA also substantially perturbs the organization and longer-range ordering of P3HT in increasing the ICBA ratio in blends. With larger and more ordered phase-separated domains, the P3HT/PCBM blend films exhibit significant optical scattering at higher PCBM ratios. Yet, such optical scattering is not significant for P3HT/ICBA blends (even with high ICBA ratios). Overall, results here suggest the reported higher efficiencies of P3HT/ICBA solar cells (vs. P3HT/PCBM cells) cannot be attributed to larger and/or more ordered phase-separated donor–acceptor domains and other characteristics play more important roles in this case.[[incitationindex]]SCI[[booktype]]電子版[[booktype]]紙

Potential applications of speed dispersion in defining freeway level of service and air emissions evaluation

[[abstract]]Speed dispersion, with respect to its statistical relationships with fundamental traffic flow parameters, is used to measure freeway level of service in the context of ‘no more than x% of vehicles with travel time up to y% greater than the free flow condition.’ It is argued that such a measure not only reflects mobility, reliability, and – potentially – safety, but also avoids the vague descriptions associated with each service level in the current US Highway Capacity Manual. These relationships are then applied to produce speed distribution estimates for the MOtor Vehicle Emissions Simulator (MOVES) model. It is argued that the MOVES model's approach limits the distribution in two speed bins, results in unsupported speed dispersion, and may cause identical distributions under various average speeds. The proposed revised approach based on speed dispersion generates specific spread-out distributions consistent with empirical data. The findings of these two applications bring new concepts to current practice.[[notice]]補正完畢[[incitationindex]]EI[[booktype]]紙本[[booktype]]電子

Evaluation of Operational Effects of Joint Managed Lane Policies

[[abstract]]This paper presents a method to evaluate the operational effects of managed lane policies—vehicle eligibility, access control, pricing, and the number of managed lanes—that form a policy combination set. Two macroscopic methods are developed to prescreen the set via simple criteria, followed by integer linear programming with multiple objectives and constraints to identify the noninferior policies among the downsized set. The approach is demonstrated on the Southern California SR-57 corridor. The application eliminates twelve of possible twenty policy combinations by the macroscopic methods, and generates four noninferior policies—the existing high-occupancy vehicle lane operation and three additional potential high-occupancy toll lane policies—in terms of maximum vehicle and passenger throughput, minimum vehicle hour traveled, and travel time variance. The prescreening efficiency of the macroscopic stage, ranging from 0 to 95%, is affected by the initial policies and traffic conditions. It is concluded that the approach can substantially assess a larger policy set and effectively identify the operational effects of joint manage lane policies.[[journaltype]]國外[[incitationindex]]SCI[[ispeerreviewed]]Y[[booktype]]紙本[[booktype]]電子版[[countrycodes]]US

Cooperative Relationships between Environmental, Energy, and Transportation Departments on Promoting Ride Sharing in Taiwan

[[sponsorship]]International Chinese Transportation Professionals Association (ICTPA); North-American Chinese Geotechnical Engineers Association (NACGEA)[[conferencetype]]國際[[conferencedate]]20110527~20110529[[iscallforpapers]]Y[[conferencelocation]]Los Angeles, C

Study of Carpool User Behaviors and Route Characteristics in Taiwan

[[booktype]]紙

What Can Taiwan's Carpool Moment Learn from U.S. Ridesharing Programs?

[[sponsorship]]International Chinese Transportation Professionals Association (ICTPA); North-American Chinese Geotechnical Engineers Association (NACGEA)[[conferencetype]]國際[[conferencedate]]20110527~20110529[[iscallforpapers]]Y[[conferencelocation]]Los Angeles, C