|Gary Fottrell, P.E.||August 29, 2002|
After reading the proposed guidelines, I would like to offer the following comments:
1. In the "Discussion of Provisions" section, Crosswalks, (1105.2), the proposal is to require the cross slope on crosswalks be limited to 1:48, except at mid-block crossings. It is noted that "It is not uncommon for streets to be constructed with constant profile grades up to 9 or 10 percent. This specification would require reduction of these profile grades to 2 percent at intersection crosswalks, thus forming "tabled areas" at intersections so that the 1:48 slope is achieved at crosswalks."
When designing a major roadway - let's say you're widening an existing 2-lane roadway to a 5-lane roadway with curb & gutter and sidewalks in a suburban area - the first thing the designer does is take the survey and design a profile. This profile is always a smooth profile, and hopefully is in accordance with the guidelines set forth in the AASHTO "Green Book". No designer that I know will interrupt his profile every few hundred feet with the introduction of the adjacent vertical curves required to flatten the grade through intersections. They certainly will not want to create a "table effect", but would, instead, want a smooth, uninterrupted profile, particularly on the primary route. On the side roads, the situation is completely different. Minor side roads are always tied in to the main route, and the result is a table effect. This is an expected condition for a minor side road, and vehicles usually are required to stop on these minor streets anyway, so the effect of a "table" is of no consequence. Cross slopes of crosswalks on side streets are usually acceptable.
I understand what the Board is trying to achieve, and, ideally, it would be great if the crosswalk side slopes could all be no more than 2%. Is this really the maximum slope that is acceptable for these cross slopes?
I believe that the "table" requirement on primary, heavily traveled routes is not feasible, and that the vast majority of crosswalks that cross major routes will continue to have cross slopes that are equivalent to the grade on the main roadway.
2. I am having some confusion concerning 1103.7.1, Detectable Warnings at rail crossings. In the "Discussion of Provisions" section, it is noted that "the draft guidelines would also require detectable warnings at the outside of each group of tracks that cross the pedestrian access route". So every time a railroad track crosses an access route, detectable warnings (i.e., truncated domes) are required to be installed. Then it notes that the warnings "would not be required at tracks sharing vehicular ways, such as street car tracks". This is all clear.
In the Draft Guidelines, Section 1103.7.1, it states "Where rail systems cross pedestrian facilities that are not shared with vehicular ways, a detectable warning shall be provided." This sentence says that when the pedestrian facility is not shared with a vehicular way, i.e., when you do not have a sidewalk with curb & gutter section along a roadway, but when you would have a pedestrian trail of some type separated from the roadway, then you would have a detectable warning. In other words, with a curb & gutter with sidewalk, you don't need the warning because the pedestrian facility is shared with the roadway. If you have a separated pedestrian trail, you do need the warning. I don't think this is what is intended to be said, according to the "Discussion of Provisions".
I could better understand it if it were stated as "Where pedestrian facilities cross rail systems that are not shared with vehicular ways, a detectable warning shall be provided in compliance with 1108." That would more closely parallel the comments made under 1103.7.1 in the "Discussion of Provisions".
3. In the Draft Guidelines, Section 1108.2.2, Rail Crossings, the text discusses the placement of the detectable warning as related to the "vehicle dynamic envelope". I assume this envelope is the edge of a moving train, plus a little extra for safety. Designers will not know what a vehicle dynamic envelope is. I recommend that the research be done that is required to determine a good number to put in place of this term.
Thank you for the opportunity to comment on the guidelines.
Also, do you know of any states that have good, ADA compatible, standard drawings of handicap ramps that I could access on the internet? I would like to try to get the one Tennessee uses redrawn to comply. If you'd like to see it, check out drawing RP-H-1 at http://www.tdot.state.tn.us/Chief_Engineer/engr_library/design/Std_Drwg_Eng.HTM
Gary Fottrell, P.E.
Federal Highway Administration
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