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HFG MARKINGS Version 1.0 MARKINGS FOR ROUNDABOUTS Introduction Markings for roundabouts refers to pavement markings on the entrances to and exits from roundabout intersections. Roundabout intersections are defined by the MUTCD (1) as "circular intersections with yield control at entry, which permits a vehicle on the circulatory roadway to proceed, and with deflection of the approaching vehicle counter- clockwise around a central island." Roundabout markings need to display clear information to incoming drivers to ensure the safe circulation of vehicles. Conflict points occur where one vehicle path crosses, merges, or diverges with or queues behind the path of another vehicle, pedestrian, or bicycle. Within roundabouts, fewer conflict points occur as compared to conventional intersections; hazardous conflicts such as right-angle and left-turn head-on crashes are eliminated. Single-lane approach roundabouts provide greater safety benefits than multilane approaches because there are fewer potential conflicts between road users, and pedestrian crossings are shorter. Robinson et al. (2) note that lower vehicle speeds entering and in the roundabout provide drivers more time to deal with potential conflicts. Design Guidelines Luminance contrast between the curb markings and the pavement should be: 2.0 or higher for roundabouts with overhead lighting 3.0 or higher for roundabouts without overhead lighting Luminance contrast is calculated by: Lstripe Lpavement Luminance contrast = Lpavement Where: Lstripe = the luminance of the pavement marking Lpavement = the luminance of the pavement RECOMMENDED ROUNDABOUT PAVEMENT MARKINGS 200 mm (8 in) 200 mm (8 in) solid white solid yellow 200 mm (8 in) 300 mm (12 in) solid white broken white 1 m (3 ft) stripe, 1 m (3 ft) gap White legend (optional) White legend (optional) 600 mm × 3 m (24 in × 10 ft) Zebra crosswalk, 200 mm (8 in) 600 mm (24 in) broken white spacing (typical) 200 mm (8 in) 200 mm (8 in) solid white solid yellow, 5 m (20 ft) spacing Source: adapted from Robinson et al. (2) Based Primarily on Based Equally on Expert Judgment Based Primarily on Expert Judgment and Empirical Data Empirical Data 20-10
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HFG MARKINGS Version 1.0 Discussion Luminance contrast: Staplin, Lococo, Byington, and Harkey (3) recommended that retroreflective markings should be applied to the sides and tops of the curbs on the splitter islands and the central island. The recommended curb contrast levels refer to the contrast between these markings and the pavement. For roundabouts with overhead lighting, a contrast of 2.0 or higher was recommended. For roundabouts without overhead lighting, a contrast of 3.0 or higher was recommended. Staplin et al. (3) state that the luminance measurements should be taken at night, using low-beam headlamp illumination from a passenger vehicle, at a 5-s preview distance upstream of the intersection. Recommended roundabout pavement markings: The pavement markings in the figure shown on the previous page are from Roundabouts: An Informational Guide (2) and differ slightly from those included in the MUTCD (1). Several markings are usually placed within roundabouts to help regulate the flow and speeds of oncoming vehicles. Such markings include broken white lines, solid white lines, solid yellow lines, crosswalk markings, and roadway marking text "Yield". Roundabout lane markings follow the logic that yellow lines denote opposing traffic and white lines denote traffic moving in the same direction. A solid white line marks the right edge of the road. Additionally, normal or fish-hook lane-use arrow pavement markings may be used on roundabout approaches as defined by the MUTCD (1). A fundamental difference between roundabouts and traditional intersections is the continuous flow of traffic at roundabouts vs. the alternating of opposing traffic flows at traditional intersections (2). This difference creates different visual demands at roundabouts, where the driver is not given the right-of-way by traffic signals. Also, pedestrians are not given signaled time to cross roundabouts. The placement of crosswalks at roundabouts is further back in order to move pedestrians out of the continuous traffic flow. This placement also reduces the visual demands for drivers who otherwise would be required to look for approaching vehicles from the left and pedestrians from the right as they entered the roundabout. With the crosswalk further from the circular area, pedestrians cross in the drivers' forward field of vision (2). Crosswalks: It is important that the crosswalks preceding the roundabout have a high degree of visibility because they are set back from the yield line. Zebra crossings are recommended because they are highly visible, distinguish the intersection from signalized intersections, and are less likely to be confused with the yield line than transverse crosswalks (2). Bicycle lanes: The MUTCD (1) states that bicycle lane markings shall not be included within the circulatory roadway of a roundabout. The figure on the previous page shows how Robinson et al. (2) suggest that bicycle lanes should be included on an approach to a roundabout. This design provides a curb ramp where the bicycle lane ends to allow bicyclists to transition as a pedestrian to the sidewalk. Robinson et al. (2) state that, at roundabouts, bicyclists can circulate with other vehicles, travel as a pedestrian on the sidewalk, or use a separate shared-use facility for pedestrians and bicyclists where provided. Design Issues Stopping sight distance: Stopping sight distance should be provided at every point within a roundabout and on each entrance and exit (2). On the approach to the roundabout, vehicles need to have a stopping sight distance to the crosswalk and the yield line. When circulating, vehicles need to be able to see that same distance around the circle. When exiting the roundabout, vehicles need a stopping sight distance to the crosswalk. The intersection sight distance is the distance that a driver without the right-of-way needs in order to see and react to conflicting vehicles before entering the roundabout (2). Because of the geometry of the roundabout, the intersection sight distance implies drivers must look over/through part of the central island. This requirement poses restrictions on the height and placement of objects and landscaping in that island; appropriate sight distance requires a clear central island. However, Robinson et al. (2) recommends that only the minimum intersection sight distance should be provided because excessive sight distance can lead to higher vehicle speeds, reducing safety for all users. Cross References None. Key References 1. FHWA (2009). Manual on Uniform Traffic Control Devices for Streets and Highways. Washington, DC. 2. Robinson, B.W., Rodegerdts, L., Scaraborough, W., Kittelson, W., Troutbeck, R., Brilon, W., et al. (2000). Roundabouts: An Informational Guide (FHWA -RD-00-067). McLean, VA: FHWA. 3. Staplin, L., Lococo, K.H., Byington, S., and Harkey, D. (2001). Guidelines and Recommendations to Accommodate Older Drivers and Pedestrians (FHWA-RD-01-051). McLean, VA: FHWA. 20-11