|Jim Mearkle, P. E.||August 28, 2002|
I'd like to comment on Section 1105.7 of the proposed accessible right-of-way
guidelines. This section requires pedestrian signals where crosswalks are
provided at left or right turn slip lanes.
1: I don't think the term "slip lane" has a consistent enough usage for it to be used in a regulation. It can be used for a free flow turn lane at an intersection, or a ramp from a freeway to parallel frontage road. If you are referring to channelized turn roadways, I would suggest that terminology.
2. Rather than mandating expensive signal installations, I suggest a simpler alternative. The AASHTO Policy on Geometric Design of Highways and Streets recommends that intersecting roadways should intersect with included angles greater than 60 degrees. Many turn roadways intersect at angles near 45 degrees. This causes problems for drivers with previous neck injuries, as they try to look over their shoulder to find a gap in traffic. Also, it moves pedestrians farther to the right, as drivers are looking to the left.
Research in the state of Florida has shown that when applied to turn roadways, this improves the safety of both pedestrians and motor vehicle drivers, as well as reducing motor vehicle delay. By making the intersection more perpendicular, pedestrians about to cross the street are more visible, lines of sight for drivers are better, and delay is less than that for a controlled ramp with a 45 degree intersection angle. Rather than requiring expensive signal installations, recommend that this safer design be used in pedestrian areas, when a free flow turn lane is not needed for capacity.
3. Have pedestrian signals been shown to improve safety? I'm not aware that they have. Rather than requiring a solution that may or may not work, state your goal - more safety and convenience for visually impaired pedestrians. That may spark innovation that would be squashed by requiring the signal. Otherwise, municipalities may simply stop marking crosswalks, which I doubt is your intent.
4. This is also true of roundabouts (Section 1105.6). These guidelines would drastically increase the cost of the most promising intersection safety advance since the Stop sign. These requirements would result in many Americans continuing to get injured or killed in crashes that could be prevented by roundabouts. In other words, the opportunity cost of hopefully, but not certainly, improving safety of blind pedestrians is more persons with disabilities from permanent injuries due to traffic crashes.
Jim Mearkle, P. E.
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