Understanding How Blind Pedestrians Cross at Signalized Intersections
Before discussing how intersection and crosswalk characteristics affect the travel of blind pedestrians, it is important to understand how blind and low vision pedestrians travel. This section gives an overview of this issue.
At any given time, people who are blind or visually impaired can travel and cross streets using a human guide, using a long, white cane to identify and avoid obstacles, using a dog guide, using special optical or electronic aids, or using no additional aid. Whatever aid is used, street crossing is comprised of a number of tasks.
- Locating the Street — First, pedestrians who are blind must determine when they reach a street. This is typically accomplished using a combination of cues, including the curb or slope of the ramp, traffic sounds and detectable warnings.
- Street Recognition — Next, blind pedestrians recognize or determine which street they have come to. This information is only occasionally provided in any accessible format, so pedestrians who are visually impaired develop a mental map and keep track of where they are within that map, usually by counting blocks and street crossings. Assistance may be sought from other pedestrians.
- Intersection Assessment — Next, pedestrians who are blind obtain critical information about intersection geometry, including the location of the crosswalk, the direction of the opposite corner, the number of intersecting streets, the width of the street to be crossed, and whether there are any islands or medians in the crosswalk. Vehicular sounds, where there is a stream of traffic on each street at the intersection, are used to infer intersection geometry.
Pedestrians with visual impairments also need to identify the type of traffic control system at an intersection. This may be determined by listening to traffic patterns through several light cycles, and searching the sidewalk area for poles with pushbuttons. However, it has become difficult or impossible to determine the type of traffic control at many intersections by listening. The inability to determine whether a crosswalk is pedestrian actuated may result in failure to use pedestrian push buttons and crossing at times other than the pedestrian phase.
- Cross the Roadway — After determining the geometry of the intersection, aligning to face towards the destination curb, determining that the intersection is signalized, and having pushed a button (where necessary), pedestrians who are blind must recognize the onset of the walk interval. In the most common technique utilized for crossing at signalized intersections, pedestrians who are blind begin to cross the street when there is a surge of through traffic on the closest side of the street parallel to their direction of travel. Once pedestrians who are blind have begun to cross the street, they must maintain a heading toward the opposite corner. Turning traffic can make it difficult to establish a correct initial heading, and in the absence of traffic on the parallel street, pedestrians who are blind may veer toward or away from the intersection.
Optimal crossing conditions occur when crossing right angle signalized intersections with a moderate but steady flow of traffic through the intersection on each leg with a minimum of turning movements.
Pedestrian actuation requires blind pedestrians to locate and push a pushbutton, then cross on the next pedestrian phase to be assured of having enough time to cross. Blind pedestrians have three types of problems at these locations:
- They cannot wait through a light cycle to assess and refine their heading by listening to vehicular trajectories, before crossing at the next pedestrian phase because they have to locate and push the button again (and re-establish their heading).
- At a location with little vehicular traffic, even if pedestrians who are blind know there is a pushbutton and use it, they may not be able to detect the onset of the walk interval if there is no through traffic on the street parallel to their crossing.
- Blind pedestrians may not be aware that there is a pushbutton and/or they may be unable to locate the pushbutton. In addition, some locations do not include a pedestrian phase, and at times when vehicular volume is low, there may not be enough time to cross the street.
In the past twenty years, significant changes in intersection geometry, signalization, driver behavior, and the technology of automobiles have affected the ability of blind travelers in the United States to obtain the information they need to cross streets independently and safely. Traffic clearing the intersection also commonly overlaps the pedestrian phase by as many seconds as the duration of the walk interval. In such cases, blind pedestrians will first perceive the pedestrian phase, and initiate crossing, after the onset of the pedestrian change interval. These changes have increased the requests for APS by blind pedestrians. Municipalities and states need a documented procedure to respond to such requests as required by the program access requirements of the Americans with Disabilities Act.
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