"Not only are more people entering and leaving the curb, but we're also putting more stuff on curbs. That 2-foot zone is getting really crowded."

State of play: This mismatch of supply and demand has spurred cities and suburbs to think about treating curbs like a public utility and charging for access to them. That includes designating more zones for ride-hail pickup and drop-off, deciding where e-bikes and e-scooters should dock — and charging more when demand is high.

Enter tech: A slew of startups see a golden opportunity to restore order to the curb with maps, data, sensors and apps.

• CurbFlow has entered a 3-month pilot project with Washington, D.C.'s Department of Transportation to monitor curbside parking.
• Passport, a curbside payment software platform, has pilots in Charlotte, Detroit and Omaha to analyze scooter usage patterns to determine how to charge for curb space.
• Inrix, an analytics firm, partnered with nonprofit Open Transport Partnership’s SharedStreets to create a standard for street-level data, including curbs.

Be smart: As a public right of way, curbs are becoming a kind of network interface for new technology and transportation options.

• Cities need to know how much of this prime infrastructure they actually have and how it's used in real time. Most cities don't have that information, because they've never actually needed it.

For example: Coord, a New York-based startup that spun out of Alphabet's Sidewalk Labs, wants to make curbs more productive — i.e., serving the most people per unit of time per length of curb. To do that, it's providing a digital database of curbs to cities.

"We're seeing a lot of cities reallocate curb space away from parking into, for example, docks for bikes. That's an easy example of improving curb productivity by serving a lot more people in that space with those bikes than you would be with just the single parked car."

Yes, but: There are trade-offs. Allocating space to e-bikes may mean fewer spaces for residential permit parking. A designated ride-hail passenger drop-off zone may take up space once used for freight and e-commerce delivery trucks.

• Eventually, autonomous vehicles will demand a piece of the space, too.
• "On most streets, there's just not enough right-of-way to give everyone — buses, bikes, scooters, pedestrians, cars — a protected zone," Tregoning says.

Meanwhile, in an ambitious and contentious bid to redevelop Toronto's waterfront neighborhood, Alphabet-owned Sidewalk Labs proposed "dynamic curbs" designed to be flexible spaces that respond to real-time traffic conditions.

How it works: The conventional cement ridge would disappear, to be replaced by lighted pavement that would direct pedestrian, cyclist and vehicle paths "on-the-fly, helping neighborhoods recapture flexible street space for public use in a clear and safe way," per the proposal.

• A "mobility management system" would set pricing based on demand and publish pricing and schedule data to third-party apps.
• During rush hour traffic, curb space would be priced high. All vehicles would pay a low fee to access the curb, with higher charges for those who wait more than 5 minutes.
• During low-demand times, the curb zone may be repurposed for wider sidewalks or pop-up street fairs. Pavement lights and signs would signal priority pickup and drop-off areas and signal which areas are off-limits for cars.

Sidewalk Labs also envisions underground drop-off and pickup zones for shared fleets or autonomous vehicles, cutting down on street-level curb idling and double parking.

• An underground network of tunnels would deliver freight packages — and carry away trash — via "smart containers" traveling on self-driving dollies. Sidewalk Labs claims this system would reduce street-level truck traffic by 72%.

The impact: Sidewalk Labs' Willa Ng predicts urban curbs will soon have to handle 8 times the current capacity.

• Even though Sidewalk Labs' plan aims for 77% of trips to be made by modes other than private cars, Ng expects transportation companies like Uber and Lyft will be heavily used.

"We're putting stress on curbs like never before, but most of [the] curbs in cities are underutilized. If we can actively manage it and set some policies to operate that curb, we can get more bang for the buck."

What's next: Toronto officials are still vetting the overall plan.

The irony: The new tech startups are cropping up to solve the curb congestion problem that was exacerbated by the last wave of gig-economy-focused tech startups, including Uber, Lyft, DoorDash, Postmates, Bird and Lime.

The bottom line: "It’s not just about curb congestion," said Jim Barbaresso, of HNTB, an infrastructure design firm. "It’s really about serving all modes in new and dynamic ways that enrich the urban experience, while also providing a safer and more accessible transport system."