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Autonomous Vehicles, Storm Water Credits, and their Impact on our Watersheds

Published onDec 24, 2019
Autonomous Vehicles, Storm Water Credits, and their Impact on our Watersheds

We have witnessed a record amount of flooding in the Mississippi River Watershed1 not only because of an increasing number of extreme weather events, but also because of the extensive tiling of agricultural fields and the pervasive paving of urban and suburban landscapes.2 The work of our interdisciplinary center—the Minnesota Design Center at the University of Minnesota—over the last several years has looked at how system transformations can have unexpected social, environmental, and hydrological benefits, engaging the fields of landscape architecture, planning, geography, policy, and engineering.

For example, we have taken part in two, interdisciplinary National Science Foundation Smart and Connected Communities grants looking at the physical-environment implications of autonomous vehicles and shared mobility services, working with colleagues in computer science, public affairs, regional planning, and civil and systems engineering.3 While much of that work has focused on transportation, it has revealed an unexpected and equally important hydrological impact that will have profound implications for our watersheds.

As happened when we shifted from horses to cars a little more than a century ago, when we moved from dirt roads to paved streets, the current shift underway from driven to driverless cars will require a similar transformation of our public rights-of-way. Research has shown that automated vehicles (AV) have a much greater precision in the path they take, without the “wander” that characterizes the way in which we drive.4 That precision can cause rapid, repetitive wear of our roadways, so much so that AV’s start to rut non-concrete surfaces within a relatively short amount of time.

That in turn suggests that we will, once again, need a different kind of road surface for the new transportation technology. We predict that the AV-ready road will consist of reinforced-concrete grade-beams following the AV tire path, able to withstand AV’s precise and repetitive routes.5 That will not only create longer-lasting streets; it will also enable the rest of the road surface to become pervious, allowing us to rethink how we deal with storm water by holding it within the roadbed itself rather than moving it through a curb-and-gutter storm water system into our waterways.

AV’s also represent a transformation in the business model of “car companies,” who now see themselves as mobility service providers as much as vehicle manufacturers.6 The shift from the production of cars to the provision of mobility-as-a-service (MaaS) will lead to a change in how we think about vehicles, not as something we must own, but instead as something we call up when needed and pay for when used.

That, too, will have major hydrological implications as the need for parking will drop dramatically as MaaS companies find it most profitable to keep vehicles moving 24 hours, transporting people during the day and packages at night. In a future transportation system in which vehicles will rarely park, surface lots and structured garages will become available for other uses, including as stormwater retention ponds and overflow basins to handle severe weather events. With even relatively dense cities like Seattle devoting 40% of its land area to parking, a significant amount of land in most municipalities will become available to clean and store water, as well as to meet other public goals, like affordable housing and open space.7

A different, but related transportation and hydrological transformation will likely occur in rural areas. There, the advent of autonomous technology in farm equipment like tractors and combines will have an impact on how many farmers will be needed in the future and where they might live. As farming continues to automate, the number of rural roads needed will continue to drop, and with that will come the opportunity to convert under-used, rural rights-of-way into bioswales and habitat corridors, a hydrological and ecological transformation that also bodes well for our watersheds. With funding from the State of Minnesota, our center has been working with small, rural communities to help them leverage their human and natural resources to attain a more sustainable economic future for themselves, of which hydrology seems always to play a part.8

While much of the transformation of our transportation and stormwater systems will happen on public land, a lot it will also occur on private property, which will require incentives to get property owners to act in the best interest of the public. Stormwater retention credit trading offers one way to accomplish this, something that research in our center has demonstrated can be an effective economic incentive for environmental ends.9 Stormwater retention credit trading allows property owners, with a lot of impervious surface and unable to handle their stormwater on-site, to buy “credits” from another property owner who has ample land and excess stormwater capacity. This offers a way for urban and suburban property owners to pay farmers upstream to take land out of food production to buffer waterways in order to reduce downstream pollution and flooding.10 Stormwater retention credits also offer a way of encouraging land owners with large surface lots that are no longer needed for parking to convert those lots into stormwater retention ponds and to get paid to do so by other property owners without sufficient land.

One of the drivers of the urban-rural divide in the U.S. comes from the collapse of the markets that once bound cities with the countryside around them. Urban residents used to buy their food and secure their lumber from the farmers and loggers in their region, in part because such goods could not travel far because of spoilage or other long-distance travel challenges. Those market exchanges not only bolstered local rural economies, but they also bound city dwellers and rural residents together and defused any animosity that might arise between them. We now buy our food and lumber from sources often far from where we live, without knowing who harvested them, which has greatly diminished the markets between urban and rural businesses. With that has come a decline in small rural communities and family farms, and a rise in the anger that some rural residents seem to feel toward urbanites, with political polarization as one result.11

For economic and environmental reasons, as well as for political ones, we need to rebuild the markets between cities and their countryside. While that can include food, through models such as community-supported agriculture (CSA), environmental resources that do not travel well, like land and water, hold the greatest promise. This is where stormwater retention credit trading offers one model. It works within watersheds, which often include cities or towns as well as rural areas, and it links impervious development to the resource that farmers have in abundance: land. The trading of stormwater retention credits also creates a flow of funding from urban to rural economies, re-establishing the market exchanges that could not only restore water quality and retain storm water to reduce flooding downstream, but also revive rural economies and start to heal our urban-rural political divide.

In sum, municipalities will see a tremendous amount of public and private land, now devoted to the accommodation of driven vehicles, become available over the next few decades and there exists a real opportunity to work in a strategic and interdisciplinary way to leverage that asset to improve water quality. We believe that this will come from linking the coming transformation in our transportation system with an equally vital transformation of our stormwater system—and just possibly transforming our political climate as well.


Thomas Fisher
Professor of Architecture, Director of the Minnesota Design Center,
Director of MS in Sustainable Design & Dayton Hudson Chair in Urban Design
University of Minnesota

This event is supported by the National Science Foundation, Award #1929601. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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