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Pedestrian detection technology has been developed for the general population to help prevent “pedestrian-vehicle conflicts” (Hughes, et al. 2001). A focus recently has been how these detection devices are being used to accommodate people with vision, mobility and physical impairments (Steindel 2008). The idea is to detect the pedestrian as they approach the intersection and activate the signal automatically. This would allow an APS to turn on the locator signal only when there is a pedestrian present. For signals that are pre-timed, this would also eliminate the walk signal being activated when there is no one at the crosswalk. Both of these reductions in sound would cut back the noise pollution caused by current APS systems.

Various methods of accomplishing this have been developed including microwave-radar, infrared, piezoelectric, video image processing and laser scanners. A number of countries have

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implemented these systems to some degree including the US, Canada, Australia, England, Japan, Sweden and the Netherlands (Steindel, 2008).

Each different type of system has its own advantages and disadvantages depending on a number of variables including the type of intersection, what is being detected and how the system is installed. Microwave or radar systems can be implemented in a number of ways but generally work on the principle of an antenna transmitting radio waves and a receiver detecting variations in the reflected signal. These variations would be caused by a moving object such as a pedestrian. One example of implementation of a microwave radar system is in Tucson, Arizona where the detectors monitor the crosswalk. If the crosswalk is still occupied during the normal end of the “walk” sequence, the time is extended by 33% to give more time to the pedestrian to clear the crosswalk. In Ottawa, Canada at least two intersections have replaced pushbutton activation of the crossing signal with microwave-radar systems that also detect whether pedestrians are still in the intersection, similar to the system shown in Figure 23. One disadvantage with this particular system is that they must be finely tuned to only respond to people on the sidewalk or in the crosswalk (Hughes, et al. 2001).

Figure 23: Detection areas for an infrared or microwave pedestrian detection system (Hughes, et al. 2001)

Infrared pedestrian detection systems work much like the microwave-radar systems, most often detecting movement to trigger the crossing signal. One of the largest installations of this type of system is in Sydney, Australia which includes about 20 intersections. This particular system uses infrared signals to detect pedestrians remaining in the crosswalk near the end of the crossing sequence. The system has now been in place for a few years, but further

installations are unlikely because the current system has issues with both false calls and justifying the costs in relation to the minimal benefits that are realized (Steindel 2008).

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Another type of system that has been used for many years in a variety of traffic applications is the piezoelectric sensor. This works on the principle of a particular material changing its electric properties when a pressure is applied. In this case, the piezoelectric sensors are placed under a mat or the paving at a corner and detect when a pedestrian is standing in the correct location. The United Kingdom and Australia have used these sensors for a number of intersections as shown for an Australian intersection in Figure 24 (Shoval, Ulrich and Borenstein 2001).

Figure 24: Piezoelectric sensor under painted area at a curb cut (Stiendel, 2008)

The last main technology that is used for pedestrian detection is video image processing.

This uses a camera to capture images and has a computer that then interprets these data into useful information. This detection has the potential to be the most accurate by using shape recognition to tell the difference between pedestrians and other moving objects like cars and debris (Steindel 2008).

Pedestrian detection has successfully been implemented in the United Kingdom, as part of a new pedestrian crossing system known as the Pedestrian User Friendly Intelligent Crossing or PUFFIN. This system does not specify technology but rather an approach that increases pedestrian safety and the efficiency in the flow of traffic. The system works using a pushbutton activated pedestrian cycle. A near side signal, meaning that the appropriate “walk” and “don’t walk” lights are on the same side of the intersection as the pedestrian, allows the pedestrian to look at both the signal and oncoming traffic at the same time. When the button has been

pressed, the “walk” signal will turn on at the next appropriate phase in the traffic. Often though, after the button has been pressed, a pedestrian will see a gap in the traffic and cross before the

“walk” sign is illuminated. Ordinarily this would mean that traffic was then later stopped when

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there was no pedestrian present. The PUFFIN system instead detects if the pedestrian crosses early and cancels the push button call (Routledge 2006).

There are two innovations with this system that can be applied to accessible pedestrian signals. The first is having the signal on the near side of the intersection. As the British

Department of Transportation says the near-side pedestrian signals allow the user to observe approaching traffic while looking at the signal and that “pedestrians with sight impairments also should find it easier to see…compared to the farside pedestrian signal (Routledge 2006).” The benefits of having a clear signal at eye level directly next to the pedestrian could assist many people with visual impairments.

The second innovation has been used for years and takes many different forms. The Puffin uses “kerbside detection to monitor when pedestrians are present and cancel demands when pedestrians cross in gaps in traffic.” (Routledge, 2006) Canceling crossing demands does not have much application in Copenhagen because according to several Copenhagen traffic engineers, most intersections are timed and the pedestrian phase is automatically incorporated in the parallel traffic phase (Bjerremose, Frederiksen, & Kreutzfeldt, personal communication, April 7, 2010). However, the widespread success of pedestrian detection in the UK makes the Puffin a good example of what is possible.

Pedestrian detection is also used in Copenhagen but because most intersections have dedicated pedestrian cycles, it is not needed as much. This setup is more common in the countryside. Copenhagen has two examples of pedestrian detection already installed. One is outside the Danish Royal Library the mid-block crossing of Christians Brygge. This crossing requires a pushbutton to activate the pedestrian signal. This is used when there is no dedicated pedestrian cycle, although few Copenhagen intersections are configured this way. Since few APS devices with pushbuttons are installed, pedestrians often forget to push the button and activate the cycle. A RADAR system was installed to detect pedestrians at the crossing, ensuring that the signal is still be triggered even if the button was not pressed. Pedestrian detection is also used outside the main gates of the Tivoli amusement park. When there are large numbers of

pedestrians, the detector allows the crossing phase to be extended so all of the pedestrians will be able to cross (Bjerremose, Frederiksen, & Kreutzfeldt, personal communication April 7, 2010).

Passive pedestrian detection for APS has advantages and disadvantages. If there are no pedestrians present at the intersection, the APS system can be safely shut off. Once a pedestrian with vision impairments reaches the detection area, the APS system is re-enabled satisfying the

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need for accessibility. This could reduce or eliminate nighttime noise pollution in areas where pedestrian traffic is uncommon during night hours. However this type of system cannot

distinguish between pedestrians who require the APS and those that do not. The noise pollution produced will not decrease as much as it would for a system that can distinguish APS users, particularly during busy hours.