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