Time was, Main and Michigan Streets were one-way conduits to rush cars and SUVs through the heart of South Bend, Ind., at the end of the workday. As God intended.

But Mayor Pete Buttigieg, now the new U.S. transportation secretary, converted downtown streets to two-way traffic, built three traffic roundabouts at key intersections, added bike lanes, and widened sidewalks.

There is a “generational opportunity” to change mobility in the nation’s cities and towns by following principles of the urbanist Complete Streets movement such as these, Buttigieg likes to say. Making it easier to walk, bike, and access transit can fight climate change while promoting racial justice, economic growth — and safety.

“There are so many ways that people get around, and I think often we have an autocentric view that forgets historically all of the other different modes,” Buttigieg said at his confirmation hearing Jan. 21.

“We want to make sure that every time we do a street design that it enables cars, bicycles, and pedestrians, and businesses … to coexist in a positive way. We should be putting funding behind that.”

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In Philadelphia, a sustainable approach to transportation became city policy under the Kenney administration. Vision Zero, for instance, aims to eliminate traffic fatalities by 2025 with traffic-calming strategies on the 12% of city roads where 80% of serious injuries and deaths occur.

The city moved a step forward Friday with a redesign of Spring Garden Street that would include parking-protected bike lanes and other traffic-calming changes. And construction is expected to begin this summer on a safety overhaul of the dangerous Washington Avenue corridor in South Philadelphia.

Buttigieg pitched South Bend’s $25 million Smart Streets project primarily as a tool to revitalize downtown and create a sense of place. Since major elements were finished in 2017, restaurants have sprouted, new hotels were built, and developers rehabbed industrial-era buildings into offices, apartments, and condos. The assessed value of downtown property rose 21% from 2013, before the project began, through 2018, an analysis by the South Bend Tribune showed.

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On the other hand, South Bend, with a population just over 100,000, has a small bus system that doesn’t run late at night or on Sundays, and Buttigieg was unable to persuade the South Shore commuter railroad to add a stop downtown. Critics point out that the relatively dear rents make the new housing inaccessible to many residents in a city with a 25% poverty rate.

Since he was nominated as transportation secretary in December, the telegenic Buttigieg has blitzed network, cable, and livestream programs advocating the goals in President Joe Biden’s proposed $2 trillion infrastructure plan, which includes 500,000 charging stations for electric vehicles and zero-emission public transit vehicles for cities.

His performance and the pull he developed as a contender for the Democratic presidential nomination have generated excitement among transportation-policy experts and advocates. But deep changes in government institutions and society are hard to achieve, and they warn the road ahead is likely to be difficult.

“We live in an intensive car culture,” said Sarah Clark Stuart, executive director of the Bicycle Coalition of Greater Philadelphia and a veteran environmental advocate. “For 100 years, all the investment and subsidization in transportation has been in roadways for cars.”

For years, the Bicycle Coalition has been frustrated by the glacial pace of change in its push for more protected bike lanes. The city’s goal was to have 20 miles of them in place by the end of this year. It has only about 10 miles.

» READ MORE: Philadelphians want protected bike lanes and pedestrian safety on Spring Garden Street

Still, Clark Stuart said, most are encouraged by the city’s adoption of the goal and are bullish on the Biden administration’s pursuit of the “progressive vision” for transportation Buttigieg is carrying.

The Department of Transportation, with a budget of about $87 billion, oversees the nation’s airways, railroads, highways, and ports, and has vast regulatory authority on everything from how many hours a trucker can drive without rest to passenger-jet avionics.

Nonetheless, there are institutional and potential political limitations on Buttigieg’s power.

A big portion of the $47 billion allocated for roads and public transit is parceled out by formulas set in law by Congress. So changing the infrastructure mix would require complex negotiations with lawmakers and the full power of the White House behind the effort.

Democrats control both houses of Congress, but their House majority is thin, and the Senate is split 50-50. The administration is pushing a $1.9 trillion coronavirus relief package as its first priority. And if an infrastructure plan is not finished by the end of the year, the 2022 midterm election cycle will take over, making it harder to get anything done.

“Americans expect us to see to it that the idea of an infrastructure week is associated with results, and never again a media punchline,” Buttigieg said in December.

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Biden took a step toward that Thursday as he met in the Oval Office with a bipartisan group of four leaders of Senate committees with a role in infrastructure funding. He warned that China has made big strides in high-speed trains and is pouring billions into electric vehicles. “If we don’t get moving, they’re going to eat our lunch,” Biden said.

Some lawmakers are worried about the costs of the two spending plans, and there is ideological resistance to the Biden team’s approach that some see as social engineering. Sen. Bill Hagerty (R., Tenn.) was one of 13 senators to vote no on confirming Buttigieg because, he said, the secretary wants to “use the department for social, racial, and environmental justice causes” instead of cutting red tape for projects that would benefit rural communities in such states as Tennessee.

One avenue for change lies in competitive grants from discretionary funds, including the $1 billion BUILD program. Secretaries of transportation have latitude to shape the criteria for awards to state and local projects.

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Eleven years ago, the Obama administration awarded money to complete the extension of the Schuylkill River Trail in Philadelphia south of Locust Street and over railroad tracks with a boardwalk and bridge.

Among items on the current wish list, advocates are aiming to get more money from the Transportation Department to help continue the building out of the Circuit Trails, a regional network of 300 miles of multiuse trails in Pennsylvania and South Jersey. The goal of a coalition of non-governmental organizations and governments is to eventually link rural, suburban, and urban communities in one of the largest metropolitan areas in the country with a total of 800 miles of trails for walking, running, and cycling.