When developing IRWL enhanced crosswalk design standards and considering "or equal" first review the video below.
There is "No Equal"
The term In-Roadway Warning Light was coined by the Federal Highway Administration during the evaluation process while considering the acceptance of illuminated pedestrian crosswalk systems as a standard into the MUTCD.
In early studies prior to the acceptance by the MUTCD, an important consideration by the California Traffic Control Devices Committee (CTCDC) was to prevent a "false sense of security" by the pedestrian when the in-pavement signal lights were flashing.
The CTCDC recognized the intent of the in-pavement warning system is to alert motorists of the presence of a pedestrian in the crosswalk. They asserted that "The biggest mistake we can make is to give the pedestrian a false sense of security." The CTCDC requested that systems be installed so as to shield the flashing lights from pedestrian vision while in the crosswalk zone in order to gain “Authorization to Experiment” approval by that State Agency. That mandate has proved to make very good sense over time and through studies conducted.
⇒ See PDF of White Paper on Unidirectional In-Pavement Signal Lights
IRWL Design Considerations
The Smart Crosswalk™ system is designed with unidirectional lights facing outwards towards the approaching motorist. The LED flashing lights are directed towards an area approximately 200' to 400' in advance of the crosswalk. The flashing signal lights merge at the eye level of the motorist in what LightGuard has coined the "Zone Of Convergence."
Our U.S. patent specifies that in-pavement signal light design for IRWL enhanced crosswalks shall have LED lights that are slightly above the surface of the road for good reason! Should road dirt, gravel or other debris accumulate around the signal light module, it provides greater assurance that the flashing light output can still be seen by the approaching motorist.
The picture of an in-pavement signal module on the right shows typical accumulation of road debris taken approximately six months in operation at an actual site. The LED lamps in our signal head light module are positioned directly behind the "Dove Prism" with a 1/2" elevation above the road surface.
This slight elevation of the signal head light module is intended to prevent the IRWL’s from being blocked by debris. This crucial aspect greatly reduces the very real potential for liability concern due to non-visibility by the motorist when critically needed. This visibility factor should be a decidedly important design consideration when specifying IRWL enhanced crosswalk systems for any type of application.
Our IRWL signal modules have a self clearing design feature called "Debris Free™" built into the base plate. These are fluted channels located across the face of the base plate.
The "Debris Free™" design allows compressed air from the impact of vehicle tires to "jet out" the accumulated rubble through the fluted air channels over time in service.
The photo on the right shows a signal module where this self clearing feature has kept the LED light clear of accumulated road trash.
As is clearly evident, even with an accumulation of debris, our slightly elevated "above grade" in-pavement flashing signal lights are clearly visible to an approaching motorist.
This is an extremely important element to consider when specifying any IRWL enhanced crosswalk system.