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St. Paul, for example, required an apartment building to have one parking space for each 1- or 2-bedroom unit, but more parking for bigger units. Meanwhile, St. Paul golf courses would need four parking spaces per hole, but their mini golf courses would need just one space per hole.

Today, these rules are gloriously gone: if you’re constructing a new building, you can build as few parking spaces as you deem prudent. In 2021, both St. Paul and Minneapolis voted to fully eliminate minimum parking requirements from their zoning codes.

By ending strict minimum parking requirements, the Twin Cities have been able to improve both housing affordability and our urban form. Based on evidence both local and from across the country, it’s becoming clear that this is a winning policy choice.

The case for eliminating parking requirements centers on the idea, largely popularized by scholar Donald Shoup, that minimum parking mandates don’t consistently reflect the actual demand for parking, relative to the cost of supplying it. The appropriate amount of parking will be different for every building based on its land cost, proximity to transit, and customer base, among numerous other factors.

In some instances, developers or tenants are willing to pay for more parking spaces than required by law, but parking mandates often result in buildings with more parking than developers would otherwise choose.

This creates a host of problems. Parking takes up a lot of space and is costly to build, whether you put it on a surface lot or in a garage (a 2021 estimate pegged the average above-ground parking structure at $27,000 per spot, and much higher if you’re digging below ground). These costs drive up rents, or else make housing projects unfeasible to build at all.

When parking mandates force excess parking spots, they also subtly reshape our transportation choices across a city. Excess parking makes car travel excessively easy, acting as a subsidy to car trips over other travel options — despite the pollution and traffic externalities that cars create. It also results in what journalist Henry Grabar terms “parkitecture,” or a sacrifice of our urban form and design at the altar of parking lots.

At the same time, eliminating parking minimums doesn’t cause off-street parking to disappear entirely. Even when apartment developers aren’t required to build parking spots, many prospective residents will still want parking (and be willing to pay for it). A world without parking requirements will still have parking, but supplied in quantities responsive to actual demand.

Recent empirical research shows how parking reform has played out in other cities. Earlier this year, researcher Catie Gould at the Sightline Institute highlighted two recent academic studies that analyzed housing developments in cities that eliminated or reduced parking requirements.

Examining Seattle and Buffalo, the researchers tracked development after parking minimum elimination to see how new buildings responded to the relaxed rules. As Gould described, Seattle and Buffalo are completely different housing markets; one is a booming coastal city while the other is an older industrial city with less than half of its 1960 population.

Yet in both instances, the majority of post-reform buildings took advantage of their new flexibility and built less parking than was previously mandated. In both cities, parking reform helped increase the overall supply of homes, reduce the cost of construction, and shift the cities toward a less car-centric design.

Since Minneapolis’s 2021 elimination of parking minimums, evidence shows that this too has been an effective change for increasing housing affordability and improving city design. A 2015 reduction in parking requirements had already sparked a reduction in the parking being built in new Minneapolis housing. Since 2021, when all parking minimums were eliminated, city data show parking construction has further declined.

The reduction in average parking spot per unit obscures an equally remarkable shift in the whole distribution of parking-unit ratios in Minneapolis. While some apartment developers have still opted to build relatively high quantities of parking, there’s been a rise in apartments with very little parking, or even none at all.

While this data isn’t comprehensively available in St. Paul, one housing project anecdotally displays the promise of eliminating parking minimums. A large apartment building on Lexington and Randolph Avenues, which sits on two bus lines and across the street from a Trader Joe’s, was initially proposed prior to St. Paul’s parking reform, with 91 housing units and 88 parking spots. When unrelated circumstances led to a redesign, the developer took advantage of the recent elimination of minimum parking requirements. The developer bumped the project up to 114 homes with 82 parking spots. More homes, less parking — and no need for a parking variance.

The short-term results of eliminating parking minimums aren’t radical, but reflect a smart change that will improve the places that we live in. In municipalities across Minnesota and across the country, strict parking minimums remain the status quo — removing or reducing parking minimums represents a promising route for reform, improving housing affordability and making our cities and towns better places to live.

Scientists in various fields have tried for years to figure out how paternal-only DNA could sustain a mammal through all stages of life.

A small team of researchers has reported a striking achievement: they succeeded in raising a mouse that came from two male parents, and it grew into a healthy adult. Their work unveils a set of genetic changes that overcomes the imprinting barriers that typically block such development.

Scientists in various fields have tried for years to figure out how paternal-only DNA could sustain a mammal through all stages of life.

Biological imprinting is an inherited pattern of gene expression. It involves certain genes getting turned on or off depending on whether they come from the father or the mother.

Researchers found that if you adjust a selection of these imprinting genes, you can open the door for unique reproductive feats, such as an embryo that starts with only paternal cells.

“This work will help to address a number of limitations in stem cell and regenerative medicine research,” explains Wei Li of the Chinese Academy of Sciences in Beijing.

In this case, the scientists homed in on key sections of DNA that are known to control fetal growth and viability.

What this means for biology

When a mouse embryo is formed in the usual way, paternal and maternal DNA come together. That combination produces a precise balance of imprinted genes.

In paternal-only embryos, certain growth-related genes can become overstimulated, but the team was able to selectively modify them so these embryos could mature.

“These findings provide strong evidence that imprinting abnormalities are the main barrier to mammalian unisexual reproduction,” said Qi Zhou, co-lead of this study.

By re-engineering the problematic gene regions, the researchers made it possible for two sets of male chromosomes to support a developing mouse. Therapeutic ideas

A number of genetic and metabolic disorders in humans stem from errors in imprinting. Scientists have asked whether strategies used here might be adapted to correct imprinting problems that cause diseases in people.

One potential target is KCNK9, which has been linked to Birk-Barel syndrome. Precise gene editing of such imprinting sites could help in the design of improved treatments for these rare disorders.

In practice, these ideas may take time to progress. Mouse models are often a first step in studying how imprinting influences development.

The more scientists understand about restoring the right imprinting patterns, the closer they might come to tackling certain medical conditions. Gene imprinting implications

The modified imprinting genes not only allowed bi-paternal mice to survive to adulthood, they also improved the efficiency of stem cells used in the process.

The researchers reported that these engineered embryonic stem cells were about twice as likely to develop into full-term pups compared to unmodified cells.

This improved developmental stability could change how scientists approach cloning. Currently, cloned animals often suffer from low survival rates and severe abnormalities, in part due to faulty imprinting.

Fixing imprinting errors ahead of time might make future cloning methods more reliable, especially in complex mammals like primates. Ethical considerations

Questions often arise about how these approaches could extend to humans.

According to guidelines from the International Society for Stem Cell Research (ISSCR), heritable genome editing is not currently allowed for human reproductive purposes because it is considered unsafe.

Researchers continue to examine these practices in animal models before even considering steps that approach human application. Investigators involved in this work remain cautious.

While a mouse with two fathers has captured headlines, translating similar methods to people is a bigger leap.

The focus remains on unraveling how imprinted genes function, and how targeted interventions might fix imprinting-related diseases down the road. Next questions

There is still room to explore how best to refine these genetic strategies to improve survival rates and lessen the chance of complications.

Specialists are also looking at future animal models to see if placental differences, organ development, or immune responses undergo subtle changes when imprinting is modified.

Some foresee that data gleaned from these methods will shape the next generation of gene-editing research.

Ongoing studies point to a need for caution. Issues like longevity, fertility, and normal physiology require much deeper evaluation.

Still, scientists see value in applying these insights to refine cloning and enhance studies of embryonic stem cells. Even partial solutions could inform safer protocols for regenerating cells and tissues in healthcare settings.

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This breakthrough was led by Wei Li of the Chinese Academy of Sciences in Beijing and Qi Zhou of the same institution, with further input from collaborators at Sun Yat-sen University.

The study is published in Cell Stem Cell.