The road as an Ecosystem in the 21st Century

Today in the Tech World, there is discussion of “platforms” and “ecosystems”. When we hear talk about Apple vs. Google, it is as much about the Apple ecosystem, particularly that around iOS, the operating system for the iPhone, vs. Android OS. The Operating Systems enable both device-based and cloud-based software services. I can buy apps that work in either eco-system, but not both (without purchasing twice). I can buy peripherals that work on one or the other, but generally not both. This mobile telephone ecosystem logic follows and is much larger than the previous decades’ PC operating system ecosystems.

Roads are a different form of economic ecosystem, and perhaps the original one. There is the ecosystem for building roads, and there is an ecosystem for those using roads. Carriers as well as private vehicles are the users. But they have a set of roadside services (energy (hay, gasoline), shelter (inns (hello Jesus), motels, and hotels), and sustenance (food)) as well as many others that are less frequently used (tollbooths, money changing, black smithing, wheel wright, vehicle repair, and so on) that are configured a particular way for users of the road ecosystem.

While the types of vehicles using roads, as well as the materials with which they are made has changed over time, the platform of the road as a place on which to hang a series of road-serving businesses is long-standing, and unlikely to disappear even as roads change with the next technological shift in vehicles.

Without roads (dirt, gravel, block, rail, asphalt, or concrete), there would not be much economy. Certainly off-road vehicles and their passengers and drivers of various kinds would still require services, but the much higher cost of travel would significantly reduce the total economic impact. Secondary economic impacts on things like manufacturing, agriculture, and non-transportation services which do depend on transportation thus depend on this eco-system as well.

There is a fascinating series of books by John Jakle and colleagues describing the emergence of the first order 20th Century Road Ecosystem: Fast Food, Motels, Gas Stations, and so on. What happens in the 21st Century with Vehicle Electrification and Automation?

We can certainly speculate that charging stations ultimately replace gas stations. Even more, vehicles may be charged in motion from the roadway.

Food production and delivery may also change in ways that are difficult to foresee. We can speculate that with automated vehicles, food may come to us in motion, rather than us stopping at the side of the road. While this synchronization, resembling the in-air refueling of Air Force One, seems far out, with full information and automated drivers, it may be quite trivial. This may or may not be a net improvement in food quality.

Why stay at a hotel when your car can move you forward in space and time while you sleep?

How else will the Road Ecosystem Change in the 21st Century?

Pathways

When forecasting the future of travel demand, we have two possible outcomes, compared to the present. People may either:

  • Travel more, or
  • Travel less

(There is an infinitesimally small possibility they travel exactly the same amount, so we will ignore that). Of course they may travel more in some places or at some times or by some modes, and less for others, so we need to distinguish between micro and macro-outcomes. That depends on changes in a variety of inputs: In travel demand forecasting we have a variety of dimensions of travel we try to model:

  • Who:
  • When: Schedule
  • Why: Purpose
  • Where: Destination
  • How: Mode, Route

If people in the future behave exactly the same as people today, and their demographics are similar, the built environment is similar, and policies are similar, and there are more of them, the travel demand model would produce roughly the same amount of travel per person, and more in the aggregate.

But that is a big “If”.  This travel demand model does not capture behavioral changes, market changes, or technology changes, for starters.

First, technology may change. A model built before a new class of modes became available cannot accurately forecast their use. For instance commercial ride sharing (“transportation network companies”, e.g. Lyft, Uber) might look like taxi, but in most US markets, taxi is so seldom used it is excluded from the model for lack of data. But it differs from taxi not only in fare (lower), but also response time (faster), whether you are sharing a ride with another party (perhaps: LyftLine, UberPool), quality of vehicle (nicer?), friendliness of driver (sociable?) and many other dimensions. That is an easy problem to identify, it is already here. Now, from a regional perspective, it may still be small enough to ignore, but who can say that will remain true in the 20 or 30 time frame of official forecasts.

Car sharing and autonomous vehicles are among the other technology shifts that are both possible and unforecasted.

Willingness to share vehicles is a behavioral question for which we have no answer about its likelihood. One of the purposes of money is to buy better services. Most people think riding separately is preferred to riding in a shared vehicle, but this is as much a social norm as a law of nature.

Willingness to travel farther when the vehicle is autonomous is something we can only guess at (theory suggests if we don’t have to exert effort in driving, we may be willing to be mobile for longer times (and distances)).

In theory we could model the supply side effects of an autonomous fleet in terms of road capacity, but we will have a mixed human-robot fleet for decades. In practice this seems quite difficult. Harder still is modeling the presence of vehicles, the response time of shared vehicles, the range of electric vehicles, distance to walk to car-sharing, and the like. Not that it cannot be done, but it cannot be done with confidence. These are a mix of technology, market, and behavioral problems which are likely to become relevant over the timeframe of forecasts.

A plausible strategy given uncertainty is to look at scenarios in addition to expected values. Instead of making the deterministic forecast that in 20 years the line will have 40,000 passengers or 100,000 AADT, consider what it will be like under a variety of different assumptions. Bureaucrats don’t like uncertainty, which is why the rules are written the way they are. Politicians will choose whatever value in the range of numbers suits their rhetorical purpose. But the public should not be mislead by the false confidence associated with forecasts of expected values given without ranges and caveats — forecasts that have historically been quite poor.

Sadly, people follow whoever expresses the most confidence, not whoever is the most accurate or honest or thoughtful. That is an evolutionary biological outcome to avoid  paralysis when the lion is actually chasing you: follow either whoever quickly decides to hold ground with spears or runs  the farthest the fastest, but don’t stand around contemplating the decision. But with new transportation investment, nothing is actually urgent.

 

 

With driving down, there’s a growing backlash against unnecessary highways | Vox.com

Brad Plumer writes about peak travel, overly optimistic forecasts, and the policy consequences at vox.com in: With driving down, there’s a growing backlash against unnecessary highways. He cites us in the closing paragraph:

Another key point was that states (and the federal government) should probably spend less money on building new roads and more money on maintaining existing roads. Economists have argued that more states should probably be doing this anyway — this Brookings Institution paper by Matthew Kahn and David Levinson makes the most comprehensive case. But the argument gets even stronger if vehicle travel is going to grow more slowly or plateau in the future.

What’s clear is that it doesn’t make much sense for states to keep planning around the idea that driving will grow at 20th century rates forever. Those predictions have been utterly wrong for nearly a decade now — and sticking with them could mean wasting billions on unnecessary roads and highways.

 

The Transportation Futures project [Open Thread]

I am pleased to announce we were awarded funding from MnDOT and the Local Road Research Board (contract pending) for The Transportation Futures Project: Planning for Technology Change:

Objective: Examine a series of technologies in-depth: autonomous vehicles; mobile telecommunications; advanced information and communications technologies; vehicles as a service; quantified self; electrification; dynamic pricing and new logistics.
Principal Investigator: David Levinson, University of Minnesota

Project Summary:
The surface transportation sector is facing a large number of technological shifts that could change how people travel. This research will explore these technologies, ascertain their potential market, consider their interactions, understand what might happen to travel demands and address how planning and forecasting should respond.

This project will develop a series of high-level policy briefs based on the analysis of each technology, its direction and its implications for Minnesota. This extends and complements the MnDOT 50-year vision expressed in Minnesota GO. It also extends the work of the NCHRP 750 project, Strategic Issues Facing Transportation, in a number of directions, and tailors recommendations to Minnesota.

As suggested, there are lots of technologies we are going to look at, from new energy sources, through autonomous vehicles, to new logistics.

Ideas however are more than welcome, as a few words cannot hope to fully capture the various directions these technologies may take, and the way policy and plans should respond.

Put your scenarios, ideas, and topics in the comments, I hope we can generate some interesting perspectives. We aim to finish this project in 2015, so it’s on a fast (for research and government) timetable.

The Evolution of the Green Line: A Retrospective

Metro Transit’s Green Line opened in June, 2014. While ridership almost immediate beat “expectations1, and the line was quickly declared “a success“, at first there were still bugs in the works related to traffic signal timings and thus overall run-time and reliability, and safety.

Though the planners felt this line on the map was permanently drawn, a review of history reveals that first lines often change over time. Investments continued to be made, and technology advanced.0

What’s happened next?  This brief article summarizes the history of how the Green Line evolved from 2014 to the present.

 

1. Transit Priority

History records that St. Paul Public Works worked very hard to ensure a safe and convenient trip for all users of University Avenue. After five years of tweaking traffic signal timings (a set of light-bulbs that instructed human drivers when it was safe to proceed), there was effective transit signal priority on the Green Line, so the line hardly ever needed to stop at traffic signals, and only stops at stations. This shaved a couple of minutes off end-to-end run times.

2. Green waves

Transit priority  added delay to cross traffic, but better informing traffic (trains, cars on University, cars on cross-streets) the speed they needed to travel to achieve the Green Wave improved overall signal efficiency and throughput and minimize stopped delays and lost time. This made travelers happier and once implemented system-wide reduced total delay by 10 percent. (History records every traffic engineering improvement reduced delay by 10 percent. This is puzzling.)

 

3. Shared space

At first, the traffic control infrastructure on the segment of the Green Line on Washington Avenue through the University of Minnesota was incredibly over-built (or counter-productively safe as one article of the era put it). Eventually, after the great traffic signal outage of 2024 (due to a widespread worm infecting centralized traffic control centers) resulted in reduced crashes, engineers had the bright idea to un-build infrastructure in many places. This gave sufficient cover for local officials to operate the Green Line through campus as a streetcar on a pedestrian mall. De-signalizing Washington Avenue turned the corridor into a shared space. Some de-busing also place, as the Campus Connector (a bus) was fully replaced by the Green Line (and the buses were rerouted to other corridors).

In a shared space, engineers finally came to realize that attention is redirected away from the hypnotic light bulbs and towards the actual other travelers. As children we are advised “Look before you leap”.  It took a few months to re-educate adults they no longer need  pay attention to the (now removed) light bulb across the street, and instead use those same eyes looking for approaching bikes, buses, and trains. The general message was  “Look before you cross”, meaning “Look. When there is nothing going to run you over – Cross. When something is going to run you over – Don’t Cross.”

The icon was a pancake on the road, with a sad face, representing the food item a pedestrian would be as flat as, if he didn’t use his eyes and brain. The use of this icon was controversial, as being insensitive, and became a symbol in the culture wars about how we treat death, but the general view was the humor and controversy made people  more careful.

4. Minimizing Conflicts – No left turns

One of the most dangerous places on the LRT line was vehicles making left turns on University Avenue across the LRT path (this was sadly a universal problem with LRT in the median, not just the Green Line). Drivers were paying attention ahead to the signal and opposing-traffic, and to their right for cross-traffic, not to their left for a train emerging from behind. In one sense, this was of course the car driver’s fault, assuming they violated the traffic control devices instructions. In another sense, engineers need to better understand human factors and design for people not machines. As the saying of the time went “Safety is a shared responsibility” – though the intent of that was to guilt travelers into behaving well, rather than the system administrators into designing for humans.)

Further, left-turns, when protected, added an additional phase to the traffic cycle, with the concomitant lost time (all-red plus extra green start-up time), wasting capacity. There were many relatively low-volume left-turns on University that could be eliminated2. This would of course have increased travel times for those who wanted to make a left (or U-) turn. Alternative solutions of the era included making 3 right turns, or a right and 2 lefts, and the space-wasting jughandle. One cannot imagine the residents on Aurora or Sherburne (the streets immediately south and north of University in the residential areas of St. Paul) would have been pleased with this option, though for streets in industrial areas in the western part of St. Paul, such Myrtle and Charles, implementation would have  been easier.

The streets below crossed University between Prospect Park and Rice Street stations. The + indicates a station, the * indicates an off-90 degree angle. The (F) indicates associated freeway entrance/exit ramps to I-94.

  • 29th* + [Prospect Park]
  • Malcolm
  • Bedford
  • Berry + [Westgate]
  • Eustis (F)
  • Cromwell (F)
  • Franklin *
  • Raymond +
  • Hampden
  • Vandalia / Cretin (F)
  • Transfer / Cleveland
  • Prior
  • Fairview +
  • Aldine
  • Fry
  • Snelling + (F)
  • Pascal
  • Hamline +
  • Griggs
  • Lexington + (F)
  • Chatsworth
  • Victoria +
  • Grotto
  • Dale + (F)
  • Mackubin
  • Western +
  • Marion
  • Rice + (F)

Traffic engineers looked at the post-Green Line traffic counts and identified Left Turns that could be eliminated. The challenge was that eliminating cross streets and left-turns diminishes access, and created more of a wall-effect than the Green Line already produces. It is unlikely this could have been done everywhere, but that doesn’t mean it couldn’t have been done anywhere. In the event, only Berry Street saw Left Turns and Through Movements eliminated in 2028. Soon after, the widespread deployment of automated vehicles mooted most of the vehicle-train interaction safety issues.

Other controls upon drivers, such as rail gates, were also proposed in the late 2010s and early 2020s as the number of vehicle-train crashes and fatalities remained persistently high, but they were not implemented before drivers were made obsolete.

 

5. Grade separations/transfer stations with arterial BRT and/or streetcars

 

As longer distance through roads with freeway interchanges, Rice, Dale, Lexington, and Snelling all had very significant levels of cross-traffic for several decades. This cross-traffic was delayed by the Green Line. The Green Line was delayed by the additional green time given to the cross-traffic (or slowed in the case of Always Green Traffic Control).

Urban diamond interchanges, with the cross streets running under University and the Green Line, allowed the following connections University WB with Cross Street NB, Cross Street SB with University WB, University EB with Cross Street SB and Cross Street NB with University EB. Upstream or downstream U-turns / roundabouts (such as at Snelling at Spruce Tree or Snelling and Sherburne) would replace the left turns. The 1 block distance was sufficient for an acceptable grade for an underpass as described.

On the outside lanes of the underpasses officials constructed  transit stations, where there would be staircase and elevator connections to the median of University Avenue and the associated Green Line Station, so transfer passengers from the Snelling Avenue A-Line BRT,  Lexington Avenue P-Line, Dale Street Zed-Line, and Rice Street Streetcar wouldn’t need to cross streets. These were planned starting in 2017 after the unexpected success of BRT, but not completed until 2034.

 

 

6. Higher frequencies

While the trains were not usually full for the first several decades (At 6 trains an hour, each with a capacity of 600 persons, in each direction, the capacity was some 3600 persons per hour in each direction, the demand was typically half that in the daily peak hour, though reached that levels for particular trains, especially if the headways got long do to bunching, and also  around events).

The constraint on higher frequencies was limited capacity in downtown Minneapolis where the Green and Blue lines share track. At 10 minute headways on each line, there was a train crossing in one direction or the other every 2.5 minutes. At 5 minutes, there would have been a train every 1.25 minutes, which would not allow much time (if any) for north-south cross traffic. The two solutions proposed for this were splitting the Green and Blue lines in downtown, so they follow different streets, or  grade separation. This was expensive (which is why it took so long to build ), but once Minneapolis decided to become an actual big city, it was constructed in 2039, the year the Minnesota Multi-Purpose Stadium was demolished (about five years after the National Football League went bankrupt from lawsuits and cancelled television contracts). A set of public playing fields replaced the site for another 30 years. Most recently, a Cyborgian Battle-Bots arena is being constructed on the site for the Minnesota Bot-Kings. Critics suggest that it is inhumane to breed and build cyborgs simply as fighting machines, and that they should be given full liberties. That has yet to happen, though a referendum is on the weekly demo-ballot later in the year.

 

7. A/B Service

In 2044 A/B service was established in peak hours. In A/B service,  trains skipped every other station (skip-stop service), so the A train would stop at Prospect Park, Raymond, Snelling, Lexington, Dale, and Rice, and the B-train would stop at Westgate, Fairview, Hamline, Victoria, and Western.  (While at first people were skeptical because of load imbalances, the additional capacities helped increase development on the “B-train” stops.

This could not have been implemented until higher frequencies are achieved (thanks to the improvements in downtown Minneapolis) without defeating the entire purpose of the added infill stations in St. Paul. With higher frequencies, A/B service ensured 10 minute headways on all stations, and 5 minutes at selected stations. Express trains, which were also discussed on the Green Line could not work without passing tracks, or the trains would bunch up as express trains approached locals. Once trains were automated (in 2064, long after cars were automated, because, well because this is transit), then the two tracks could be more efficiently utilized to allow passing.

 

8. Service Extensions 

The Southwest Green Line extension was opened in 2023, several years behind schedule due to lawsuits and tunnel cave-ins. Demand was less than expected at most suburban stations for many years. The 2047 rezoning in Minneapolis  allowed the area around the Chain of Lakes to explode with new high rise development, and the Kenilworth station became the busiest on the Line.

The Blue Line extension to the Northwest suburbs opened in 2022. The nature of the routes allowed interlining, so eventually half the Green Line trains went to Edina Prairie (the merged cities of Eden Prairie and Edina) and half to Brooklyn (the merged cities of Brooklyn Center and Brooklyn Park). City mergers were encouraged by state government as part of the municipal consolidation movement to reduce the number of mayors the Governor had to meet with every year. Similarly every other Blue Line train went to each city. The routes were informally dubbed Green Prairie and Green Lyn, and Blue Prairie and Blue Lyn.

A service extension to the East, across the Kellogg Bridge (rebuilt in 2031 for a second time), extended the Green Line to the Metropolitan State University campus, and then down East 7th street for a few miles.

In 2030, a spur, from Stadium Village stations, along the Campus Transitway, connected the Falcon Heights campus of the University of Minnesota (UM-FH) and the State Fair Grounds through Energy Park, to the Green Line, and on to Downtown Minneapolis, running every 10 minutes. This was dubbed the Maroon Line (the name Gold Line having already been used up on a Freeway BRT in the east Metro.) The University secretly acquired the St. Paul Ports Authority (which had been privatized in 2023), and redeveloped many sites, especially at the Raymond Avenue station of the Maroon Line.

9. Express trains

In 2049, the new Minnesota Magnetic Levitation Commission began running fast, high-frequency express trains between downtown Minneapolis and downtown St. Paul, on a right-of-way other than the Green Line. This created point-to-point travel times on the order of 15 minutes between the downtowns, instead of 40-50 minutes that the Green Line afforded.

This intersected the Green Line at the railroad tracks between Transfer and Prior (the once (and future) Amtrak station), behind a the ruins of a chain store called Menard’s. This site created  a natural transfer station, especially as that area was redeveloped from industrial to the new development dubbed “Transfer Town” was built simultaneously (in fact, the value capture from Transfer Town helped fund the short MagLev line. (There were other stations at the University of Minnesota-Dinkytown Campus (UM-DT) and at Snelling Avenue, as well as termini adjacent to existing stations  in downtown Minneapolis (The Grand Central Interchange by Target) and St. Paul (The Union Depot by Dunkin’).

While there was probably little  significant time advantage of the MagLev over high-frequency Bus-on-Shoulder or Bus on MnPass lanes on the I-94 corridor, there was so much extra rail right-of-way capacity in the region that this was proposed along with radial lines, as part of a Minnesota MagLev passenger network. MagLev was selected as the need for new right-of-way and infrastructure was made apparent after the rail passenger hostage crisis of 2029, when Burlington Northern Railway held up 200 passengers on three different trains of the Northstar line so a line of high-fructose corn syrup tank cars could pass, which sadly led to a derailment and toxic waste emergency, also known as the Great Corn Sugar Flood.    Ultimately it made sense to build the line with the highest demand (between Minneapolis and St. Paul) first, before the spokes.

 

10. The Green Line is disbanded.

In 2074, sixty years after it first opened, the tracks of the Green Line were ripped up, and the last train cars sent to the Hennepin County Nano-bot Materials Recovery Center for smelting and recycling into a nutritional supplement for Cyborgian Battle-Bots dubbed Soylent Green. Remember Soylent Green is trains.

Plans now call for the abandoned right of way itself to be turned into a high-speed bike way (the University Greenway and downtown VeloTunnel). Bicycling has soared in popularity since climate control was implemented globally a few years back, ensuring urban winter days would be above freezing, and summer days well below human body temperature.

The parallel road, University Avenue, has been replaced with grass, and is used for low elevation robotic hover-jitneys (Ro-Ho-Ji), which have proved much more popular than the Green Line in recent years. These can be summoned simply by yelling the phrase (Ro-Ho-Ji) into the air, the network of microphones deployed across the metropolitan area will quickly identify your location via triangulation and recognize your voice, allowing for quick dispatch of the Ro-Ho-Ji and automatic billing. Drunkards continually yelling Ro-Ho-Ji late on Thursday nights to celebrate the weekend remains a problem, but voice recognition identifies them and special vehicles (Ro-Ho-Ji-Al) for the inebriated scoop them up for insta-sobering.

The “Please Check Schedules” electronic message signs at stations, that never worked properly, and became iconic on tee-shirts and coffee mugs, just like the London slogan “Mind the Gap”, finally showed the correct schedule on the final day of operation. Internal documents posted on WikiLeaks after the closure, revealed that Metro Transit, and later the Green Line Corporation (which operated the line its last 30 years), were able to make the signs work after the first year, but kept them broken to appeal to tourists.

At the closing of the Green Line,  a ribbon was symbolically sown back together.

 

Footnotes:


0.
Nothing was ever finished except to the politicians. Politicians were elected officials in the representative governments of the era who ran for re-election every 4 years. Recall these were eliminated with the Sester-centennial Direct Democracy Constitution Convention of 2026. Politicians interacted with public works when they had their photo (a static two-dimensional image, often black and white) snapped at the ribbon cutting for a new line  every 10 years. The photo was important  the “above the fold” headline in the newspaper (a pile of printed paper left outside the home of older residents, mostly filled with advertisements for stores (places where people would purchase goods) as well as a record of the events of the previous day).

1.
“Expectations” are technically “calculations”. I hesitate to say “forecasts”, since people in the field didn’t actually believe them. These calculations for the Green Line complied with then relatively conservative FTA standards, which tightened in response to studies in the 1990s and that found forecasts were severely optimistic. Compare 1980s forecasts for Hiawatha LRT with later forecasts.  The Alternatives Analysis predicted ridership of 37,000, the Final EIS lowered this number to 24,800. See Table 7 http://www.fta.dot.gov/documents/NSPA2007_Final(1).pdf . These new methods led to somewhat more accurate forecasts … the incentive then became to have the lowest forecast that would still have gotten your project funded. Since the controls on forecasting methods reduced the incentive to lie in order to get funding, if you could beat forecasts after opening, and you could immediately declare success, that helped with the next project. Higher forecasts arewerestill useful for justifying additional spending of course, but spending limits were constrained politically.

 

2.
Berry Street, I am looking at you.

Cross-posted at streets.mn.

Ridership projections reveal tricky calculus for transit planners | strib

I get quoted in the Strib by Eric Roper:  Ridership projections reveal tricky calculus for transit planners (though I wish he would clean up my conversational  speech so it looked better on paper. This is why interviews should be by email). Also he used “calculus” in an article.

Prof. David Levinson, a transportation expert at the University of Minnesota, said there is a valid reason for the conservative projections.

“All the forecasts that were done in the 70s, and 80s and 90s…most of them overestimated transit ridership,” Levinson said. “The forecasts that have been done since the new rules have been implemented have gotten much closer to expected ridership numbers.”

That helps federal funders, he said, but also creates some confusion about what exactly the forecasts represent.

“To call that the forecast means that everything will exceed forecast if there’s any economic development affects whatsoever, because you’re not accounting for any of them [economic development effects] or very little of them when you’re doing this,” Levinson said.

It stands in contrast to the city’s projections for a Nicollet-Central streetcar line, Levinson said, which has been sold as an economic development tool.

“I would claim that the streetcar forecasts are more in the line of advocacy forecasting. They were trying to get people to buy into the idea of this,” Levinson said, noting that they would likely have to be adjusted if the project advances in a quest for federal funding.

The forecasts may be about to change, however. John Welbes, a spokesman for the Southwest project, said new ridership estimates will be released between mid-August and early September.

The Futurist Fallacy

As I occasionally write about the future in this blog, I try to keep in mind what I will call “The Futurist Fallacy” –   In the future, everyone will live and behave like  the futurist does today.

Contrast this with William Gibson’s quote: “The future is already here — it’s just not very evenly distributed”, which he is reported to have first said this in an interview on Fresh Air, NPR (31 August 1993).

Both of these may hold provided that the futurist is not in fact behaving the way future will turn out. Of course every good futurist will try to behave in a future-oriented way, trying to be cutting edge with technologies and lifestyles. Many of those will however turn out to be techno-evolutionary dead ends.

 

 

Imagine: A World Where Nobody Owns Their Own Car – Eric Jaffe – The Atlantic Cities

Eric Jaffe at Atlantic Cities writes: Imagine: A World Where Nobody Owns Their Own Car :

“Skeptics have also charged that autonomous cars will disrupt any city-based travel models, since people freed from the need to drive will move even farther away from the core. That might be true for people who own their autonomous cars, says University of Minnesota transport scholar David Levinson, but a strong sharing system could promote the opposite movement. “If you’re paying for the car by the minute, then you’re not going to want to move farther out,” says Levinson. “You’re going to want to move closer in.”

Levinson says SAV service that offers convenient on-demand trips gives people a much greater incentive to rely on that system — and a much smaller incentive to take the unnecessary trips often made by private cars. It’s a recipe for the type of multi-modal lifestyle change only possible right now in places like Manhattan. Transit for essential daily trips, cabs (or other alternatives based on the type of trip) for the rest.”

The big market question is when this world will begin to emerge. Levinson subscribes to a timeline in which autonomous cars enter the luxury market in 2020, the technology trickles down into the affordable mid-level range over the next several years, and by 2030 every [edit: NEW] car on the road is driverless. (Other cars would be banned a decade later.) Since car- and ride-sharing operations tend to rely on smaller cars, that would peg SAV networks closer to 2030 — about 16 years from now.

“It’s not that far away anymore,” says Levinson. “But 16 years ago was 1998, and Google hadn’t been invented. So it’s a short time and it’s a long time.”