According to the ADAAG, detectable warnings must be used at junctions between
the pedestrian path/accessible route and a vehicular path. The intent is to
warning a pedestrian with a vision impairment of the roadway edge in the
absense of other edge cues (curbs, landscaping, street furniture, etc.) The
detectable warning is not to 'locate' a crossing, but to warn of the vehicle
traffic. For these reasion, DWs should be used a ramps leading to access
aisles for on-street parallel parking.

Detectable warnings are intended to provide a cue to a blind person that he or
she is about to leave a pedestrian area and enter a vehicular way. They do not
serve as wayfinding devices. Curb ramps at on-street parking spaces are not
the same as at spaces in a parking lot where one might simply enter an
accessible parking space access aisle. If there is no vehicle parked in an
on-street space, one could potentially walk down a curb ramp and end up in the
street. Detectable warnings are needed on all curb ramps in the public
right-of-way.

Dennis - I agree; however, if the curb ramp (with detectable warnings) is
solely there to access the parallel on-street parking and is not a "crossing",
couldn't it be misleading (in the pedestrian thinking that this is a safe place
to cross)?

I also agree. Unfortunately there are many false assumptions that people make
about curb ramps. Some believe that the detectable warnings indicate the
direction in which people should cross the street (such as a skewed angle).
Although we try as much as possible to have curb ramps within the crosswalk
markings and to generally be oriented in the direction of the crossing, it is
not always achievable with large corner radii where curb ramps have to be
perpendicular to the curb or existing features.

Dennis and Dean are correct. The primary purpose of the detectable warning is
to define the transition between the sidewalk and the street on the pedestrian
access route and to provide a cue for that transition where the curb or other
barrier would be. The ADAAG definition of a detectable warning is, "A
standardized surface feature built in or applied to walking surfaces or other
elements to warn visually impaired people of hazards on a circulation path."
The current Draft Public Rights-of_Way Accessibility Guidelines defines
detectable warnings as "A surface feature of truncated dome material built in
or applied to the walking surface to advise of an upcoming change from
pedestrian to vehicular way."

Interesting discussion for sure. I think it would be wise to consider what
visually impaired pedestrians expect when they encounter a DW; what are they
being taught or told with regard to interpeting situations where a DW is
present. From what I have discerned a DW informs the pedestrian that they are
either entering or leaving a space that is shared with motorized vehicle
traffic. One such example outside the context of a curb ramp is the use of DWs
at the queuing areas to transit stops such as subways, trains, etc. The key is
to send a uniform message to the pedestrian, everywhere and every time. I have
been thinking for some time now that DWs ought to be included in the Manual on
Uniform Traffic Control Devices (MUTCD) for this reason. Perhaps in the future
there will be various tactile surfaces that send different messages, but in the
meantime, the presence (and absence?) of DWs must always mean the same thing
regardless of where they are lcoated. So, what are the vision impaired being
told or taught to expect when they encounter a DW?

The DW in a transit station does not mark the staging area; it functions the
same as on a street curb ramp: it indicates that you are in the pedestrian area
(platform) and that, if you continue, you will enter the vehicular area
(trackbed) which may be hazardous to your health! DWs do not mark locations to
cross; that is judged by using other cues such as traffic surge, APS sound, etc.

MUTCD Markings Committee has been debating adding DWs to the Manual.

In California we have a requirement for directional tiles in addition to DW
material at the edge of tranist platforms at the staging areas:

At transit boarding platforms, the pedestrian access shall be identified with a
detectable directional texture. This detectable directional texture shall
comply with Figure 11B-23B and shall be 0.1 inch (2.54 mm) in height that
tapers off to 0.04 inch (1.02 mm), with bars raised 0.2 inch (5.08 mm) from the
surface. The raised bars shall be 1.3 inches (33.02 mm) wide and 3 inches (76
mm) from center-to-center of each bar. This surface shall differ from adjoining
walking surfaces in resiliency or sound on cane contact. The color of the
directional texture shall comply with Section 1121B.3.1, item 8(a). This
surface will be placed directly behind the yellow detectable warning texture
specified in Section 1121B.3.1, item 8(a), aligning with all doors of the
transit vehicles where passengers will embark. The width of the directional
texture shall be equal to the width of the transit vehicle's door opening. The
depth of the texture shall not be less than 36 inches (914 mm).

I would like to emphasize what Dennis said, "DWs do not mark locations to
cross; that is judged by using other cues such as traffic surge, APS sound,
etc."

The intent of DWs is to provide a tactile cue to the blind/low-vision
pedestrian that they are leaving a pedestrian way and will potentially be
stepping out in front of a vehicle. Crossing a street, at a crosswalk or other
location (jay-walking), is a separate matter that is, just as Dennis stated,
guided by a set of other cues including sounds of traffic patters (stop/start
movements), sounds of perpendicular traffic (or lack of), APS, Vibro-tactile
signals, etc.

In my opinion, if you are installing a ramp that leads into a vehicular way for
on-street parking, street crossing, etc., truncated domes must be installed.