Technical Details

Please refer to our prototype see this proposal in more context.

Process Overview for Creating an Open APS

We will create a website that lets anyone generate APS assets for free. Given an intersection and crosswalk, we will use the NYC Centerline Data Set to look up the crossing width, presence of bike lines, and traffic direction and the propose content for:

  • Physical sign - street name, braille, arrow
  • Audio description - what is said when the sign is pressed

The user can edit this suggested information, then click to download assets. We will generate:

  • Vector files:
    • Sign
    • Braille on sign (optional)
    • Raised arrow on sign (optional)
    • Enclosure (includes unique ID and QR code)
  • Flash drive image for Raspberry Pi, including intersection-specific audio and software

The user can physically “print” the APS by sending our vector files to a CNC machine (like a Glowforge).

As for the software, the user just needs to copy the flash drive image onto a micro SD card and insert it into the Raspberry Pi - it will automatically start when powered up.

Website Flow Mockup

Step 1: Pick intersection, crosswalk, and direction

Pick intersection

Step 2: Modify Suggested Content

We lookup information about this interesection, but allow users to edit with any updated information.

Update Content

Step 3: Download Generated Results


This is a zip file, which uncompresses into a folder with a README; SVG files for visual assets; and a .iso file for the software image.

Step 4: Copy Software onto SD card

Insert a blank SD card into your computer, and copy the software image onto it. We recommend using Etcher (a free, open-source tool that makes this easy)..


Step 5: Use CNC tools to cut physical sign

Use the included vector graphics files to cut the sign and enclosure. As a reminder, the vector files look like:

Sign Vector Graphic

Box Vector Graphic

As needed, you can modify these files using the free and open-source tool Inkscape.

Step 6: Assemble and Install

Follow our easy instructions to:

  • Assemble the enclosure
  • Attach wires to the Raspberry Pi
  • Insert the SD card into a Raspberry Pi
  • Plug it it

The APS should start working immediately.

APS modes: full crosswalk guidance, or orientation-only

The APS can be configured to operate in one of two modes:

  • Full crosswalk guidance: we are connected to the crosswalk light status (walk, changing, don’t walk) and can give guidance on whether it is safe to cross.
  • Orientation-only: we provide location and orientation information, but do not give crosswalk guidance

The full crosswalk guidance (with walk/don’t walk instructions; LED walk/don’t walk lights; and vibration) mode is only possible if the APS is connected to the intersection crossing light state via a hardwired connection. Otherwise, we will provide orientation instructions (audio of street name, cross-street, and crossing hazards) but will not provide guidance about when it is safe to cross.


Do you make money from Open APS?

No. We provide the website and tools for free, and we truly believe that this is a beneficial product idea that could help New York City, and other cities. We’re not entirely altruistic; we do consulting work (for accessibilty and software) and hope this will spread our reputation as problem-solvers and innovators.

Who benefits from the Open APs?

Everyone, of all abilities.

Sighted people still often have trouble spotting street signs, or seeing the traffic signals when a vehicle is blocking the way. Having a large-font sign at the crosswalk just makes sense.

For low-vision, blind, and deaf-blind people, our solution is not only an improvement over the existing APS solution in terms of features and richness, but it is a fraction of the cost and could be more quickly and widely deployed, yielding massive accessability improvements in the urban experience.

Does this need power?

Yes; this device uses about 3 watts. We recommend connecting it to a wired power source, though a solar-charged battery solution may be feasable.

A backup battery is a worthwhile consideration. This would provice several hours of functionality even if power goes out.

What are the connectivity requirements?

None - the Open APS works offline. We are open to discussing over-the-air-update solutions, but caution that this may add to the cost of goods and complexity.

How do we detect the crosswalk light state?

This device will be connected to the crosswalk signals using a hard-wired connection. Although this may add to installation costs, we regard this as a critical safety issue. While many lights operate on stable timing patterns, we want to avoid any possible safety issues caused by changes, clock skew, power outages, etc.

Does the computer hardware need to be Raspberry Pi?

No. The Raspberry Pi is great for prototyping purposes, but our core software concept is fairly simple and should be easy to port to any number of platforms. Note that that more advanced features, like a Bluetooth Beacon, might be more involved on certain platforms.

Has this device been tested against extreme weather conditions?

No. This is a prototype proof-of-concept. We acknowledge that weatherization, temperature, and vandal-proofing require significant consideration and testing; on the other hand, there exist many standarized enclosures that should be easy to re-purpose for this kind of device.

Why have a QR code and unique ID?

By “stamping” each device produced with a unique ID which can be easily looked up online (throught the QR code) and associated with the precise intersection and location information, we believe we are opening the door to future innovation and easier maintainence costs. There are no obvious downsides, and any number of new uses cases this promotes.

What would the beacon do?

The beacon isn’t the core of our idea, but having a stable digitial “marker” at a particular known physical position opens the doors to any number of future innovations. Moreover, the beacon may increase the general public’s engagement with these devices in general, opening to doors to conversation and education.