#465 PedPal Lite: An ATSC-Independent Safe Intersection Crossing App

Principal Investigator
Stephen Smith
Start Date
July 1, 2023
End Date
June 30, 2024
Project Type
Research Applied
Grant Program
US DOT BIL, Safety21, 2023 - 2028 (4811)
Grant Cycle
Safety21 : 23-24


PedPal is a smartphone app designed to assist pedestrians with disabilities in safely crossing signalized intersections, developed originally as part of the Federal Highway Administration’s Accessible Transportation Technology Research Initiative (ATTRI) [1,2].   PedPal interacts directly with the surtrac adaptive traffic signal control (ATSC) system operating at the intersection using real-time traveler-to-infrastructure (T2I) communication and standard DSRC messaging to provide crossing support to its user.  Upon arrival at the intersection, PedPal receives and presents information to its user about the intersection’s geometry, crossing options, and current traffic signal state. When the user indicates her crossing intent, the app then communicates this information to the intersection (eliminating the need to locate and push a pedestrian call button), along with how much time is required by the user to safely cross the intersection. In response to receiving this information, the traffic signal system will set the pedestrian crossing time in the desired direction to ensure that upon getting the crossing signal, the user will receive crossing time that has been requested. More advanced PedPal capabilities include the ability to monitor user crossing progress in real-time, to recognize when the user is traveling slower than expected, and to trigger the traffic control system to dynamically extend the crossing time in such circumstances. The PedPal app is integrated with the smartphone's native accessible features and provides visual, auditory and haptic interaction modalities. 

This project focuses on producing a cheaper and more broadly deployable version of PedPal. Whereas the ability exploit surtrac’s real-time ATSC capabilities enable advanced capabilities such as dynamic extension of the current phase duration that enhance safety, its deployment cost to municipalities presents a significant barrier to widespread deployment of the PedPal technology. Furthermore, a recent UTC funded project centered on technology support for the 'complete trip' has expanded the scope of PedPal's capabilities in several new safety-related directions, none of which depend on interaction with surtrac.

To foster more widespread deployment of the PedPal technology, this project will develop and pilot test a stand-alone version of PedPal (referred to as ‘PedPal-Lite’) that will interact directly with the hardware controller at the intersection via an ATSC-independent PedPal intersection manager. This manager will take over responsibility from the Surtrac ATSC system both for broadcasting information about the intersection and the current traffic control state to the smartphone app and for interacting with the traffic controller in response to messages received from the app, exploiting the same underlying T2I connectivity. The manager will run on a low-end processor residing in the cabinet at the intersection and will take advantage of the V2I-hub software module developed under sponsorship of FHWA to generate DSRC formatted messages for broadcast to PedPal users. To maximize deployment potential, we will focus integrating the PedPal intersection manager with controllers that support standard NTCIP interaction protocols.

We will demonstrate and pilot test the developed PedPal-Lite variant on a TBD intersection near the CMU campus that is running a conventional fixed signal timing plan on a hardware controller that supports the NTCIP standard.


Strategic Description / RD&T
This proposal addresses the “Zero Fatalities” Grand Challenge (Ch. 1, p. 3) and one of its desired outcomes (Ch. 2, p. 16): “People no longer accept a high risk of fatality or serious injury as a cost of mobility.”The project aligns with the US DOT RD&T primary purpose of “Promoting safety” (Ch. 1, p. 5) and with the US DOT strategic goals of “Safety” and “Transformation” (Ch. 1, pp. 5-6). Each of these strategic goals is dealt with separately below.
Safety: The proposal addresses two of this goal’s research priorities: Human Factors & Data-Driven System Safety (Ch. 2, p. 17, Table 3). Under the Human-Technology Interactions heading of Human Factors, it “Explore[s] the effects of new technologies, including automation, on travel behaviors" (Ch. 2, p. 18).Under the Safety Technology heading of Data-Driven System Safety, it “Leverage[s] innovative technologies to monitor, predict, and plan ways to reduce injuries and fatalities among the transportation workforce and traveling public" (Ch. 2, p. 19).
Transformation: The proposal addresses one of this goal’s research priorities: New and Novel Technologies (Ch. 2, p. 50, Table 6). Under the Automation heading of this priority, it “Conduct[s] research to develop an effective and efficient safety assessment framework for automated systems across all modes of transportation” and “Develop[s] best practices for safe interaction of automated roadway vehicles with existing vehicles, … pedestrians, cyclists, and motorcyclists” (Ch. 2, p. 60).
Deployment Plan
During the first quarter, we will develop a conceptual design for the overall PedPal-Lite system. We will consult with Miovision and pathVu, our industrial deployment partners to ensure that the system functionality incorporates capabilities viewed as essential to each partner's separate deployment collaborations with Stephen Smith's research lab to maximize the potential of successful and widespread deployment - in the case of Miovision through our collaborative development of an Intersection Safety system (ISS concept) for submission to the DOT Intersection Safety Challenge, and in the case of path, through our joint pursuit of a pilot deployment in Sacramento County (who has applied for Federal SMART program funds) of a smartphone app that integrates safe-intersection crossing and accessible routing functionality. Development of the system design will also place emphasis on minimizing system deployment cost, to lessen the barrier to widespread deployment. Finally we will seek feedback from pathVu in its role as our equity partner, to further ensure wide deployment among its target user population (pedestrians with disabilities).

During the second quarter, we will implement the PedPal-Lite system design and test its functional capabilities in the lab

During the third quarter, we will continue testing and refining the system in the lab while developing an experimental plan for performing a field test of the PedPal-lite system. We will work with the Pittsburgh Public Works Department to identify an intersection that utilizes a compatible intersection controller and is currently running a conventional fixed signal timing plan. Once appropriate conditions and permissions have been obtained for carrying out the field test design, we will proceed to configure the PedPal-lite system at this intersection and evaluate its functional capabilities in the field. Finally, we will develop plans for transitioning our technology results to each of our deployment partners (hopefully by this time with concrete deployment opportunities in hand).
Expected Outcomes/Impacts
We believe the PedPal-Lite technology that this project proposes to develop will have a profound effect on increasing the safety of pedestrians with disabilities, by lowering the cost of deployment and making this technology support for safe intersection crossing accessible to pedestrians with disabilities in a more equitable manner.  Separation of dependencies on advanced ATSC system technologies significantly hinders the ability of municipalities to make such smartphone based apps  an option for pedestrians with disabilities. By eliminating this cost barrier, this problem is overcome. Further, a system design that emphases equitable accessibility to such apps allows all pedestrians some access to safe intersection crossing and more generally other broader scoped complete-trip capabilities. For example, one point of discussion with our pathVu deployment partner (and current collaborator) has focused on providing a design that can fall-back and provide (at least a more limited set of functional capabilities) if acquisition of a state of the art smartphone is beyond the potential user's financial means and a lesser mobile phone alternative is the only possibility for gaining access.

In the longer term, analogs of the PedPal-Lite system design could be adopted for other classes of vulnerable road users (e.g., cyclists) which can lead to even greater increase in overall safety at and around intersections
Expected Outputs
This project will produce a smartphone app that safe intersection crossing and broader complex trip technology support  to pedestrians with disabilities in a form that is ready-made for inexpensive, and more broadly scoped deployment in large urban settings. The PedPal-Lite app will operate at a much broader class of intersections including intersections that operate with conventional fixed signal timing plan. By focusing on integrating with a class of controller types that adopt interaction protocol standards, widespread deployment is explicitly emphasized.

We also expect this project to yield a conceptual system design that can subsequently be adapted to provide similar technology support of out classes of vulnerable road users.
Using keywords that included
- smartphone apps 
- safe intersection crossing
- technology support for pedestrians with disabilities
- and combinations of the above 

The TRID search returned a relatively small set of records, with most actually consisting of references to our previous work on the variants of the PedPal smartphone app, and of those other references that were returned, all but 1 or 2 were clearly not related to the current PedPal-lite effort. Chen-Fu Liao (U. of Minnesota) is another earlier smartphone app focused on pedestrians with disabilities. I have seen this work before. In contrast to the PedPal app, it focuses more narrowly on vision impaired, and even then only provides basic functionality for user selection of a crossing direction and indication when the crossing phase has begun. Pedpal in contrast supports pedestrians with different types of disabilities, and also provides more advanced capabilities for visually impaired individuals such as detecting and responding to user movement outside of the crosswalk, and signaling the presence of pedestrian presence in the crosswalk to approaching CAV vehicles.

There is also recent work at building a smartphone app for intersection crossing (not found in this search) performed by Larry Head's group at the University of Arizona. This work similarly uses real-time T2I communication and has been demonstrated in the field. However this app does not focus on pedestrians with disabilities, and is restricted to accepting desired crossing direction and announcing when the phase for that direction becomes active. This app is also fundamentally linked to their priority based traffic signal control scheme, which could also impose a cost barrier to wide scale deployment.

Individuals Involved

Email Name Affiliation Role Position
sfs@cs.cmu.edu Smith, Stephen Robotics Institute PI Faculty - Tenured


Amount of UTC Funds Awarded
Total Project Budget (from all funding sources)


Type Name Uploaded
Data Management Plan PedPal-Lite-Data-Management-Plan.pdf Oct. 16, 2023, 1:14 p.m.
Publication Probabilistic 3D Multi-Object Cooperative Tracking for Autonomous Driving via Differentiable Multi-Sensor Kalman Filter April 1, 2024, 9:43 p.m.
Presentation Technology Support for Pedestrians with Disabilities April 1, 2024, 9:43 p.m.
Progress Report 465_Progress_Report_2024-03-31 April 1, 2024, 9:43 p.m.

Match Sources

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Name Type
Miovision Inc Deployment Partner Deployment Partner
pathVu Inc. Deployment & Equity Partner Deployment & Equity Partner