Guide for Roundabouts (2023) / Chapter Skim
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Pages 55-74
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From page 55... ...
4-1 Contents 4-2 4.1 Pedestrians 4-3 4.1.1 Pedestrian Safety and Quality of Service 4-5 4.1.2 Accessibility 4-7 4.1.3 Pedestrians' Use of Roundabouts 4-7 4.2 Bicyclists and Micromobility Users 4-9 4.2.1 Bicyclist Safety and Quality of Service 4-9 4.2.2 Bicyclists' Use of Roundabouts 4-10 4.3 Passenger Cars and Motorcycles 4-10 4.3.1 Driver Characteristics 4-11 4.3.2 Drivers' Use of Roundabouts 4-11 4.4 Large Vehicles 4-15 4.4.1 Designing for Versus Accommodating Large Vehicles 4-15 4.4.2 Standard Trucks 4-16 4.4.3 Oversize or Overweight Trucks 4-16 4.4.4 Buses 4-16 4.4.5 Other Large Vehicles 4-17 4.5 Emergency Vehicles 4-17 4.6 Railroads and Light Rail Transit 4-18 4.7 Connected and Automated Vehicles 4-18 4.8 References A successful roundabout meets the needs of people who travel through it. Early project planning must account for each of these users -- from people traveling on foot or using personal assistive devices to drivers of the largest motor vehicles.
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From page 56... ...
4-2 Guide for Roundabouts these configurations may also result in more complex roundabouts that increase the crash frequency for motorized users. This chapter presents an overview of roundabout user groups along with their associated characteristics.
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User Considerations 4-3 Exhibit 4.2 illustrates a pedestrian navigating a roundabout. Exhibit 4.3 illustrates pedestrians and bicyclists using a shared-use path at a roundabout.
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4-4 Guide for Roundabouts • The number of motor vehicle travel lanes and the proximity to a pedestrian facility. • The number of motor vehicle lanes that a pedestrian must cross.
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User Considerations 4-5 crossings at all types of intersections. This occurs when the driver in the first lane stops to yield to a pedestrian, blocking the sightlines between the pedestrian and vehicles in the next lane.
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4-6 Guide for Roundabouts • They need curb ramps that intersect the roadway at approximately 90 degrees so that wheels reach the bottom of the ramp at the same time; if only three wheels are in contact with the surface, they lose some control and stability and may tip over. They cannot readily negotiate a vertical discontinuity more than 0.5 inches (13 mm)
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From page 61... ...
User Considerations 4-7 4.1.3 Pedestrians' Use of Roundabouts Exhibit 4.4 provides suggested guidance on how pedestrians should use a roundabout. 4.2 Bicyclists and Micromobility Users Biking has long been a component of the transportation system.
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From page 62... ...
4-8 Guide for Roundabouts Bicycle facilities at roundabouts need to be compatible with the surrounding bicycle network and adjacent land-use context. Depending on context and roundabout configuration, the surrounding roadway network may serve bicyclists in a variety of ways: • In the roadway, sharing a lane with motor vehicles; • On the shoulder adjacent to motor vehicle lanes; • In bicycle lanes adjacent to motor vehicle lanes; • In bicycle lanes at the same grade but laterally buffered from motor vehicle lanes; • In physically separated bicycle one-way or two-way facilities, sometimes known as cycle tracks or protected bicycle lanes; and • In shared-use paths with pedestrians, separated from the roadway.
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From page 63... ...
User Considerations 4-9 4.2.1 Bicyclist Safety and Quality of Service As with pedestrians, safety performance and quality of service are interrelated for bicyclists. The quality of service for bicyclists reflects how people riding bicycles perceive their ability to safely travel along a facility or through an intersection.
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From page 64... ...
4-10 Guide for Roundabouts 4.3 Passenger Cars and Motorcycles Passenger cars are the most common users at most roundabouts in the United States. Passenger cars include light-duty trucks with two axles, such as vans, minivans, pickup trucks, and sport utility vehicles (27)
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From page 65... ...
User Considerations 4-11 For older drivers, FHWA's Highway Design Handbook for Older Drivers and Pedestrians presents the following considerations for understanding the differences in older drivers and how those differences may increase their need for education and traffic control signing, as well as design considerations (28)
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From page 66... ...
Rule of the Road Example Legislation Using turn signals on exiting 1) A person commits the offense of failure to use an appropriate signal for a turn, lane change or stop or for an exit from a roundabout if the person does not make the appropriate signal under ORS 811.395 (Appropriate signals for stopping, turning, changing lanes and decelerating)
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From page 67... ...
User Considerations 4-13 that can drive legally on the roadway without special permits and vehicles that either require permits, such as oversize or overweight (OSOW) vehicles, or vehicles that otherwise have large dimensions, such as some farm equipment.
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4-14 Guide for Roundabouts LOCATION: NW 319th Street/I-5 Southbound Ramps, La Center, Washington. SOURCE: Kittelson & Associates, Inc.
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From page 69... ...
User Considerations 4-15 4.4.1 Designing for Versus Accommodating Large Vehicles Large vehicles often affect key roundabout dimensions that are dictated by the clear width of the large vehicle's swept path and its ability to turn at a minimum radius. This is especially true for single-lane roundabouts, where the swept path of the truck may be the critical design dimension in many parts of the design and may dictate which parts of the roundabout need to be traversable by trucks.
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From page 70... ...
4-16 Guide for Roundabouts The truck fleet in the United States has evolved in recent years. A national study of the truck fleet and its characteristics found that the combination of a tractor and a single large trailer (WB-62 through WB-67, depending on the length of the cab and placement of rear axles on the trailer)
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From page 71... ...
User Considerations 4-17 4.5 Emergency Vehicles Roundabouts provide emergency vehicles the benefit of lower vehicle speeds, which may result in reduced crash risk compared with non-roundabout, signalized crossings. In roundabouts, unlike at signalized intersections, emergency vehicle drivers do not face unexpected through vehicles entering the intersection, resulting in angle crashes at high speeds.
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From page 72... ...
4-18 Guide for Roundabouts Unlike signalized intersections, most roundabouts do not have an option for clearing the queue on a roundabout approach before a train's arrival. Without the ability to clear the queue on an approach to a roundabout, motor vehicles may occupy a rail crossing when the train arrives.
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User Considerations 4-19 7. (Proposed)
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From page 74... ...
4-20 Guide for Roundabouts 27. A Policy on Geometric Design of Highways and Streets, 7th ed.
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