|Scott Batson, P.E.||August 12, 2002|
Below please find my comments regarding proposed modern roundabout accessibility rules:
1105.6 Roundabouts. Where pedestrian crosswalks and pedestrian facilities are provided at roundabouts, they shall comply with 1105.6.
1105.6.1 Separation. Continuous barriers shall be provided along the street side of the sidewalk where pedestrian crossing is prohibited. Where railings are used, they shall have a bottom rail 15 inches (380 mm) maximum above the pedestrian access route.
Comment: The guideline as specified is too broad. No guidance is provided regarding the boundary for where a roundabout intersection begins or ends and thus a barrier begins or ends. The nature of a roundabout intersection is similar to a curved section of roadway or a mid-block crossing. The requirement of a street-side barrier at a roundabout intersection to separate vision impaired pedestrians from the roadway seems arbitrary. The logical extension of such need for barrier would be to install barriers at the edge of every sidewalk which is adjacent to a street. No substantive argument or evidence has been provided that distinguishes a modern roundabout pedestrian crossing as inherently less safe than any other mid-block crossing design or intersection treatment, and thus warranting such barrier. Location of the pedestrian crossing can be accomplished with a depressed landing adjacent to the ramp that directs pedestrians into the marked crossing.
1105.6.2 Signals. A pedestrian activated traffic signal complying with 1106 shall be provided for each segment of the crosswalk, including the splitter island. Signals shall clearly identify which crosswalk segment the signal serves.
Comment: The guideline as specified is too broad. The guideline appears to apply to all sizes and types of roundabouts with pedestrian facilities regardless of the level of auto or pedestrian traffic use. As roundabouts have so many different applications, with a similar variety of pedestrian environments, a single protocol without regard to traffic volume or the number of entry or exit lanes a pedestrian is expected to cross will unduly limit the modern roundabout's application due to the cost of this guideline. This would be unfortunate as modern roundabouts have a clear record of reducing total crashes and crash severity as compared to standard signalized traffic control. I would suggest additional research into the methods used in Australia and Europe, where modern roundabouts are used at high pedestrian use locations with regular frequency.
The guideline singles out the modern roundabout intersection control geometry without a clear argument or evidence of a safety need. The logical extension of this guideline is the need for pedestrian actuated signals at all intersections, regardless of traffic volume.
Scott Batson, P.E.
Senior Engineering Associate
Portland Office of Transportation
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