Hainan Li

Normal Deceleration Behavior of Passenger Vehicles at Stop Sign–Controlled Intersections Evaluated with In-Vehicle Global Positioning System Data

Deceleration characteristics of passenger cars are often used in traffic simulation, vehicle fuel consumption and emissions models, and intersection and deceleration-lane design. Most previous studies collected spot speed data with detectors or radar guns. Because of the limitations of the data collection methods, these studies could not determine when and where drivers began to decelerate. Therefore, the studies may not provide an accurate estimation of deceleration time and distance. Furthermore, most previous studies are based on outdated and limited data, and their conclusions may not be applicable to the current vehicle fleet and drivers. The normal deceleration behavior of current passenger vehicles is evaluated at stop sign-controlled intersections on urban streets on the basis of in-vehicle Global Positioning System data. This study determined that drivers with higher approach speeds decelerated over a longer time and distance. Higher initial deceleration rates were also associated with higher app...

NORMAL ACCELERATION BEHAVIOR OF PASSENGER VEHICLES STARTING FROM REST AT ALL-WAY STOP-CONTROLLED INTERSECTIONS

Acceleration characteristics of passenger cars starting from rest are often used in traffic simulation, modeling of vehicle fuel consumption and emissions, and design of intersections, acceleration lanes for entrance terminals, turning bays, and passing lanes. Most of the previous studies developed four different acceleration models: the constant acceleration model, the two-phase model, the linear-decreasing acceleration model, and the polynomial acceleration model. However, most of the studies were based on outdated and limited data, so their conclusions may not be applicable for the current vehicle fleet and drivers. The normal acceleration behavior of current passenger vehicles starting from rest at all-way stop-controlled intersections is evaluated, and the previous acceleration models are verified with recent observations. A comparison is included between the acceleration behaviors of straight and turning maneuvers and the influence of speed limits on acceleration rates, and two new polynomial models are developed for driver acceleration behavior for turning maneuvers versus straight maneuver acceleration from a stopped condition.

Operating-Speed Model for Low-Speed Urban Tangent Streets Based on In-Vehicle Global Positioning System Data

Low-speed urban streets are designed to provide both access and mobility and to accommodate multiple road users, such as bicyclists and pedestrians. However, speeds on these facilities often exceed the intended operating speeds, as well as their design speeds. Several studies have indicated that the design speed concept, as implemented in the roadway design process in the United States, does not guarantee a consistent alignment promoting uniform operating speeds less than design speeds. A promising design approach to overcome these apparent shortfalls of the design speed approach is a performance-based design procedure with the incorporation of operating speeds. However, this approach requires a clear understanding of the relationships between operating speeds and various road environments. Although numerous previous studies have developed operating-speed models, most of these studies have concentrated on high-speed, rural two-lane highways. In contrast, highway designers and planners have little informat...

Methodology for Developing Transit Bus Speed-Acceleration Matrices for Load-Based Mobile Source Emissions Models

An emissions model for transit bus based on road load estimates emissions as a function of transit bus power demand for given transit bus activities and environmental conditions. Transit bus speed and acceleration rates are key activity parameters and are the most important parameters in the estimation of transit bus power demand, also known as engine load. Once the transit bus engine load is calculated for a given speed and acceleration, emissions in grams per vehicle hour can be calculated with grams per brake-horsepower hour emission rates. However, collecting speed and acceleration data on various road types and times of day requires extensive efforts for use in load-based mobile source emissions models. To quantify Atlanta regional transit bus speed and acceleration rates, the Georgia Institute of Technology research team installed trip data in a transit bus operated by the Metropolitan Atlanta Rapid Transit Authority. The team collected second-by-second speed and location data for 3 weeks on a varie...

Geographic and Demographic Profiles of Morning Peak-Hour Commuters on Highways in North Metropolitan Atlanta, Georgia

During the summer of 2006, license plate data on morning peak-hour commuters were collected to assist with the creation of a potential participant pool for the congestion pricing phase of the Commute Atlanta (Atlanta, Georgia) instrumented-vehicle study. The Commute Atlanta study needed to identify census block groups with the highest probability of yielding study participants eligible for recruitment. Approximately 17,000 unique vehicle registration addresses in a six-county area were obtained from the license plates of vehicles observed traveling on several metropolitan Atlanta highways. The data collection enabled further geographic and demographic analyses of peak-hour commuters at the census block group level, providing new insight on limited-access highway commutersheds and demographic characteristics, such as the census block group income distribution, the travel modes, and the travel times of the highway-based commuters who contributed substantially to the regions traffic congestion and worsening air quality. Observation sites were located near the intersections of radial highways and a perimeter highway encircling Atlanta at a 10- to 12-mi radius from the downtown central business district. On average, commuters registered their vehicles (and presumably lived) 13 mi from the observation sites. The registration addresses were located a mean straight-line distance of 4.2 mi from the centerlines of the highways on which they were spotted. Demographically, highway commuter households had incomes 14.4% higher than the average household income, although this percentage varied by observation site. They were less likely to carpool or use nonautomobile forms of transportation on their journey to work, but they were more likely to work at home. Highway commuters were also more likely to report longer travel times to work than their neighbors in the census survey. These findings have implications for congestion pricing and related equity concerns.

Instrumented Vehicle Measured Speed Variation and Freeway Traffic Congestion

This paper investigates the characteristics of speed variation obtained from speed profiles of GPS-equipped instrumented vehicles driven by the participants of the Commute Atlanta Project, an ongoing instrumented vehicle research program deployed in Atlanta, Georgia. In particular, this research effort examines the relationships between acceleration noise and the level of traffic congestion on freeway segments. The results of this study may provide another prospective use of Vehicle Infrastructure Integration (VII) data which are likely to play a significant role in monitoring traffic congestion.