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Fall 2011

Smartphone research aims to help visually impaired pedestrians

Blind Pedestrian

ITS Institute researchers are working to put a powerful suite of assistive technologies at the fingertips of visually impaired pedestrians. The prototype Mobile Accessible Pedestrian Signals (MAPS) system uses technologies built into the latest smartphones—including Global Positioning System (GPS) receivers, digital compasses, and wireless networking—to help people with limited or no eyesight cross intersections safely.

The MAPS concept takes a new approach to assistive technology for intersection crossing. Because MAPS puts the assistive technology directly in the hand of the user, the system avoids many of the drawbacks associated with conventional infrastructure-based Accessible Pedestrian Signals (APS) while offering greater flexibility and ease of use.

Minnesota Traffic Observatory (MTO) senior systems engineer Chen-Fu Liao worked with graduate student Avanish Rayankula to develop the MAPS concept. Former research associate Michael Rakauskas helped Liao evaluate a survey to determine what information blind pedestrians need.

MAPS research shows how advances in handheld devices are changing the way we think about personal assistive technologies, whether for drivers or pedestrians, says ITS Institute director Max Donath. (The Teen Driver Support System concept developed by Institute researchers is another application of smartphone technology to a transportation safety problem.)


Signal technologies to assist visually impaired pedestrians have been around almost as long as electric traffic signals themselves. Signals that provide auditory cues first appeared in the United States as early as the 1920s, not long after the first electric traffic signal was installed in 1914. It was not until the 1970s, however, that Accessible Pedestrian Signals (APS) were widely deployed in the U.S. Attached to the top of pedestrian signal displays, these so-called “pedhead-mounted” units initially used two different auditory indicators to distinguish north-south and east-west crossing signals. National standards for APS were finally established in the 2000 edition of the Manual on Uniform Traffic Control Devices.

The most recent APS systems incorporate a repeating push-button beacon sound to help users find the crossing-request button; push-button units are equipped with a raised arrow indicating the direction of crossing and may provide a tactile indication of the walk signal in the form of vibration to assist users in noisy environments. Some systems can even adjust the volume of the auditory signal in response to ambient noise levels. 

But despite these improvements, APS systems attached to traffic signal structures have several inherent drawbacks, including the cost of equipment and maintenance as well as complaints from nearby residents about the sound produced by the systems. From a usability perspective, because there is no standard location for push-button signals, visually impaired pedestrians must deviate from their preferred travel paths to request a crossing signal, which can make navigating the intersection more difficult.            

Currently, infrastructure-based APS remains controversial within blind communities. While some organizations support the idea that APS can provide useful additional information for visually impaired pedestrians, others argue that current APS technology does not adequately address the needs of the visually impaired and the complexity of crossing an intersection without visual cues.

The MAPS system

The prototype smartphone application was developed using an Android developer phone, the HTC Magic, which offers features required by the MAPS concept: digital compass, GPS, accelerometer, WiFi, and a text-to-speech (TTS) interface.

Like other assistive-technology systems developed by ITS Institute researchers, the design of the MAPS system reflects the goal of helping users make better decisions. MAPS is not intended to serve as a user’s only means of navigation, but to complement the orientation and mobility (O&M) training and techniques used by blind and visually impaired people.

In use, a MAPS unit monitors the user’s position using GPS and collects information about traffic signal timing and phasing automatically when the user approaches a MAPS-enabled intersection. The prototype system uses the SMART Signal roadside data collection system developed by civil engineering professor Henry Liu, but future versions will interface directly with advanced traffic signal control units via the emerging Digital Short Range Communications (DSRC) networking standard for transportation applications.

To compensate for weak GPS signals at certain intersections, particularly in urban environments where tall buildings can interfere with satellite reception, MAPS is designed to connect to Bluetooth geo-ID modules at each intersection corner to determine the user’s location. The MAPS application combines current signal information with an onboard geospatial database containing information such as intersection geometry, street names, the number of lanes in each street, and the direction of travel on each street.

While standing at an intersection, the user can point a smartphone in the direction he or she wants to cross and call up information about the intersection and the signal phase by tapping the unit’s touchscreen once. A double tap confirms the desired crossing direction and sends a request for a crossing signal to the traffic signal controller. Feedback is given to the user via the TTS interface.

In a series of experiments designed to determine how well smartphone sensors could track the position and heading of MAPS users, the limitations of current sensors were readily apparent in the form of significant position and heading inaccuracies. The development of more precise sensors and enhancements such as Bluetooth geo-referencing modules can improve performance; the research team also envisions the development of new algorithms to improve dead-reckoning and image processing techniques using smartphone cameras to detect crosswalk “zebra” striping. Ultimately, however, the MAPS system will be most usable when combined with the user’s knowledge of navigation techniques.

More information about the development of the MAPS prototype is available in a research report published by the ITS Institute: Development of Mobile Accessible Pedestrian Signals (MAPS) for Blind Pedestrians at Signalized Intersections (CTS 11-11), available from the ITS Institute website.