An understanding of the relationship between lane width and traffic operations is important in making decisions about urban and suburban arterials. Numerous geometric elements, including lane width, affect the saturation flow rate at an intersection on an urban or suburban arterial. Several studies have been conducted to evaluate the relationship between lane width and saturation flow rate at intersections. This relationship is investigated on urban and suburban signalized intersection approaches by using field-study sites with the most ideal conditions possible. Research results indicate that saturation flow rate varies with lane width. Average saturation flow rate was in the range of 1,736 to 1,752 passenger cars (pc)/h/ln for 2.9-m (9.5-ft) lanes, 1,815 to 1,830 pc/h/ln for 3.3- to 3.6-m (11- to 12-ft) lanes, and 1,898 to 1,913 pc/h/ln for lane widths of 4.0 m (13 ft) or greater. These measured saturation flow rates are generally lower than those currently used in the Highway Capacity Manual (HCM). Furthermore, the percentage difference in saturation flow rate between sites with 2.9- and 3.6-m (9.5- and 12-ft) lanes was about half the value used in the HCM. Because data were limited to queue lengths between 8 and 11 vehicles, the research results do not directly address queue lengths longer than 11 vehicles.
The paper presents the results of research undertaken to evaluate how the safety performance of intersection approaches with channelized right-turn lanes compares with that of intersection approaches with conventional right-turn lanes or shared through and right-turn lanes. Crash data for nearly 400 intersection approaches in Toronto, Ontario, Canada, including intersection approaches with channelized right-turn lanes, conventional right-turn lanes, and shared through and right-turn lanes, were analyzed to compare the safety performance of the three right-turn treatment types. The research results indicate that intersection approaches with channelized right-turn lanes appear to have similar motor vehicle safety performance as approaches with conventional right-turn lanes or shared through and right-turn lanes. This result was found both at the downstream end of the channelized right-turn lane (where the right-turning vehicle merges with the cross street traffic) and at the upstream end of the channelized right-turn lane (where the right-turning vehicle begins the right-turn maneuver). Intersection approaches with channelized right-turn lanes also appear to have similar pedestrian safety performance as approaches with shared through and right-turn lanes. Intersection approaches with conventional right-turn lanes have substantially more pedestrian crashes (approximately 70% to 80% more) than approaches with channelized right-turn lanes or shared through and right-turn lanes.
Right-turn deceleration lanes reduce the potential for rear-end collisions from vehicles slowing to make right-turn maneuvers. Right-turn lanes also improve arterial capacity by removing slower-moving vehicles from the main traffic stream. Transportation agencies must have an understanding of the traffic operational and safety effects of right-turn lanes to determine effectively where right-turn lanes are needed. Therefore, in this research, a computer simulation study of motor vehicles and pedestrians at right-turn lanes was conducted to determine their operational effects. A benefit-cost analysis of right-turn lanes that considered both their operational and safety effects was performed. The research indicates that right-turn maneuvers from a two-lane arterial at an unsignalized intersection or driveway can delay through traffic by 0 to 6 s per through vehicle where no right-turn lane is present. Delays to through traffic due to right turns in the same situation on a four-lane arterial are substantially lower, in the range from 0 to 1 s per through vehicle. Pedestrians at unsignalized intersections or driveways can have a substantial impact on delay to through vehicles due to slowing of right-turning vehicles yielding to pedestrians. Provision of a right-turn lane can reduce pedestrian-related delays to through traffic by as much as 6 s per through vehicle, depending on pedestrian volume. Also presented is an economic-analysis procedure that can identify unsignalized intersections and major driveways at which provision of right-turn lanes is cost-effective.
A significant amount of delay to transit vehicles in urban areas is caused by traffic signals. Implementation of signal priority has the potential to reduce control delay caused by traffic signals. The implementation of these systems requires engineering studies that address both transit and traffic signal operations. A comprehensive program requires coordination between the transit agency and the transportation department to address needs of both agencies and users. The City of Portland and the Tri-County Metropolitan Transportation District of Oregon (Tri-Met) have been working on a program that exhibits the elements of such an effort. This article details the efforts of the project and the methodology for developing signal timing and detection distance settings.
Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FRA, FTA, Transit Development Corporation, or AOC endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. DISCLAIMER The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research. They are not necessarily those of the Transportation Research Board, the National Research Council, or the program sponsors. The information contained in this document was taken directly from the submission of the author(s). This material has not been edited by TRB.
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