Good (Geo)Fences Make Good Neighbors

By Paul Steely White

Effective geofencing is crucial to making micromobility safe and successful. Making geofences work requires on-board computing and granular maps made in collaboration with local officials.

Shared scooters continue to be a polarizing addition to city streets around the world. I’ve found that people either love them or hate them. For many, their opinion is largely dependent on the rider behavior they’ve witnessed; a lover can turn to a hater if they see too many scooters encroaching on the pedestrian zone, blocking access ramps, or speeding on walkways. Pedestrians have too little space as it is, so as e-scooters become increasingly more accepted, they’ve got to stay out of the pedestrian right-of-way.

To date, the micromobility industry has “answered” this concern with a combination of somewhat-effective products and over-the-top or unsustainable promises. Current proposed solutions include rider education, parking photo verification, incentives to park in designated areas, ubiquitous street teams that move errant scooters, and even autonomous scooters that redistribute and park themselves.

Of all the pedestrian-friendly assurances companies make to cities, the geofence is the most heralded. But what exactly is a geofence?

Simply put, geofences are a set of rules or actions linked to a specified geographic perimeter. In the case of micromobility, once the perimeter and rules are in place, our regulatory partners (i.e. cities) should expect automatic enforcement in those zones. This is way more appealing and reliable than just counting on individual riders to follow the rules.

Figure 1. A geofence “rule book” stores regulations per ride zone, designated by lat. and long. coordinates

Though often treated as a panacea, the fact is that current geofences just don’t work as advertised. Just ask anyone who’s visited the Santa Monica beach bike path — a popular destination for pedestrians, runners, and families, and the site of the nation’s first shared e-scooter geofence. Despite operators’ best efforts, and the exhortations of city officials, the path is still rife with errant scooters.

There are two main reasons why companies have fallen short of fulfilling their geofencing promises: The inherent inaccuracy of GPS, and the time-consuming cellular communication lag between the scooter and the cloud.

Inherent GPS Inaccuracy

GPS could be called Gross Positioning System because at best it has a margin of error of 8–15 feet. And that’s if you are in Nebraska on a sunny day far from tall buildings. It’s even less accurate in “signal shadow” areas like urban central business districts. Even when GPS is working well, it is still not precise enough to capture all the nuances of a city’s unique built environment. So, even at its very best, it’s clear that GPS can’t reliably discern the boundary between adjacent streets, sidewalks and bike lanes.

Vehicle-Cloud Communications Lag

Compounding the inherent limitations of GPS, almost all geofence offerings rely on cellular connections to communicate a scooter’s position and determine, on a cloud server, whether it is within the virtual boundaries of a restricted zone. Then, a message needs to be sent back from the cloud to the scooter via a cellular connection with instructions regarding what speed limit it should enforce. This cloud-based reconciliation via cellular network takes anywhere from 6–30 seconds to complete. Because scooters can travel 15 mph (20 feet per second), riders are often hundreds of feet into a restricted area before the geofence actually kicks in. Sometimes, this round trip of communication takes several minutes to complete, due to limitations in cellular reception, or errors in data packet delivery.

So, What About Beacons?

Many companies have promised more reliable geofencing by offering Bluetooth beacon technology. When it comes to improving signal accuracy, beacons work. The problem is that they can be prohibitively expensive. To be effective, they’d need to be placed every 50 feet. Each individual beacon costs tens to hundreds of dollars, and requires outdoor installation throughout a city’s street network, which could easily put the cost of preventing sidewalk riding for a city like Bristol into the millions of pounds.

LINK’s Approach

Rather than rush to market with bad geofencing technology or promise prohibitively expensive hardware installations, LINK’s parent company, Superpedestrian, spent years building an alternative approach that, instead of relying on a cellular connection, uses unique, ground-truth maps that are installed in each scooter.

Ground Truth Maps

Superpedestrian’s Ground Truth Maps are custom digital base maps that we make in concert with city partners to capture unique, granular features of the urban landscape.

Before every launch, we work closely with local city planners to evaluate their needs. If GTMs are deemed essential, our engineering team uses specialized equipment to capture a city’s unique built environment (eg. a pedestrian plaza adjacent to a bike path), which we can improve over time based on field input to adjust for GPS inaccuracies. Our team collects data block-by-block, accounting for weather and temporal variations. Because every city is unique, we supplement our maps by consulting city experts and residents who help us hone in on particularly problematic areas. We merge these data sets with existing digital maps to create highly granular GTMs composed of thousands of small polygons (res-13, for the enthusiasts reading this), which are then overlaid with restrictions and/or speed rules per city regulations. Because the boundaries between streets, sidewalks, bike lanes and plazas can often shift, periodic updates to GTMs are critical to maintain a high level of compliance.

On-board Integration

GTMs are loaded on-board every LINK scooter so that the vehicle can distinguish between restricted and unrestricted zones in real-time without relying on a cellular connection to the cloud. Our scooters come equipped with five microprocessors that work together to quickly synthesize GPS, GTM, and geofence rule book information. This allows LINK to enforce geofences in real time rather than several seconds or minutes after one of our scooters approaches a restricted zone. (Figure 2)

Figure 2. LINK enforces geofences within 1 second while others experience significant enforcement lag

In practice, LINK’s on-board map can perform in extremely nuanced regulatory situations. Consider this stretch on West Temple Street in Salt Lake City, which includes a street, a bike lane, and a sidewalk. (Figure 3)

Figure 3. LINK optimized a geofence in SLC to accommodate different zones on adjacent streets and sidewalks

As depicted by the color-coded hexagons, a LINK rider in Salt Lake City who attempts to ride from the street onto this busy pedestrian sidewalk sees their scooter safely slow to 3 miles per hour, the average pedestrian walking speed. Notably, this does not impact riders in the bike lane on the street, who can ride up to 15 miles per hour, per city policy.

Wondering if these geofences actually work?

Figure 4. No bologna here — that geofence worked just as intended

Fulfilling the Promise of Micromobility

In theory, small electric vehicles have unparalleled ability to replace short car trips and support multimodal trips. For this promise to become a reality, safety is essential. This requires more accurate and reliable geofencing. It also requires a safer scooter that “knows” when it has a mechanical or electrical issue. I’ll cover that in my next post. See you on the street!

--

--

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store