About one quarter of Toronto's land area is streets and sidewalks, and how the city uses that enormous resource will help determine how it develops in the decades to come.

At a time when cities are recognizing that mobility is no longer primarily about cars, Toronto is preparing to select a new leader for the transportation department. It's one of the most important roles in the bureaucracy, with the ability to shape the city, and the choice will send a message about the future Toronto wants to build.

Mayor John Tory called it "an extraordinarily important" position for the city to fill. "I don't think there's any issue that people want us to deal with and that we have to deal with on a more kind of urgent and consistent basis than transportation and mobility," he said in an interview.

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A position that could once be somewhat invisible, heading a transportation department is now widely recognized as key to urban success. Helped by the examples of Gabe Klein, in Chicago and Washington D.C., and New York's Janette Sadik-Khan, the ability of a strong and progressive transportation leader to make a city more liveable is increasingly clear.

"You have to play the short game on the street outside," said Seleta Reynolds, general manager of transportation in Los Angeles, where she is stickhandling the Great Streets project aimed at turning roads into places where people can come together.

"You have to deliver, deliver, deliver things that people can see, things that make people's lives better, things that get people talking."

In an earlier time, roads were for moving cars and the main job of city bureaucrats was to make sure motorists weren't slowed down. But cities are changing. Mobility is changing. Toronto has made initial steps in this direction, with the introduction of some protected bicycle lanes and dedicated transit corridors. And the prospect of bigger change looms, from the emergence of driverless cars to carving out space for pedestrians on Yonge Street.

This file has been overseen since 2012 by Steve Buckley, Toronto's general manager of transportation services. He is returning to his native Philadelphia at the end of this month, though, and an international search to replace him is now under way. His successor is expected to be in place by late this year.

To get a sense of how the next transportation leader could affect the city, The Globe and Mail talked to urban experts, consultants and people who have played this role in other large cities. All said that the job brings enormous challenges and opportunities, and will require an understanding of how cities are changing.

"Our streets have to be more than just for moving cars, because that's not making the best use of this incredible asset we've got," Ms. Sadik-Khan said from Oakland, Calif., where she was doing work for the urban-affairs consultancy Bloomberg Associates. "Running a transportation department isn't just about timing the [traffic] signals any more, it really is about looking at the entire street and finding ways to make all the pieces fit together."

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The challenges are large for cities of Toronto's vintage. Like some of these other places, Toronto developed distinctly different characters in various parts of the city, with different densities and sizes of roads and preferred methods for getting around.

Mr. Klein acknowledged the "horrible planning decisions" made by many North American cities in the middle of the 20th century. He argued, though, that it's up to transportation leaders to show residents that these mistakes can be rectified and to start showing progress as quickly as possible.

"It's as prominent [a role] as the mayor and the transportation commissioner make it," he said from Washington.

"There's an incredible amount of power if you harness it. If you don't harness it it can just be a seat that gets kept warm and not much innovation happens. But mayors want more innovation. They understand that when you change your streets – when you make them people places, not just places for [vehicle] throughput and cut-through traffic – that you create incredible places, and therefore economic growth."

A necessary question in Toronto, though, is how receptive the city and its politicians might be to a hard-charging and progressive transportation leader.

This is a city where road tolls are politically toxic, even as transit fares keep outpacing inflation. It's a place where some councillors worry about the environmental impact of bicycle lanes and where the prospect of dedicating space for transit on King Street, the busiest streetcar route in the city, remains controversial.

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Deputy city manager John Livey, to whom Mr. Buckley's replacement will report, praised the outgoing transportation head for his "foundational" work modernizing the department. He believes that Toronto is increasingly open to different ways of doing transportation, pointing to the recent cycling plan as one example.

"I think people are gung-ho," Mr. Livey said. "Certainly council is, certainly the mayor is. I think the public is."

For his part, Mr. Tory acknowledged that he is "never going to be a radical agent of change," and that Toronto's "timidity" can work against major shifts. But he argued that evolving mobility and work patterns, and the approach of driverless cars, make it necessary to act.

"The notion that we're still going to have in 10 years, or should have or even can afford to have, the same infrastructure for transportation that we have today, I recognize the fact it's not on," he said. "But then the question becomes, all right, well, how quickly can you change it? Both in terms of the [political support for] it and in terms of the affordability."

Cherise Burda, director of the Ryerson City Building Institute, said that the future of King Street will be a sort of philosophical "litmus test" for the city's next transportation leader.

"We manage traffic and we manage a city designed for cars. And then we have a mayor who's fairly dedicated to car travel, in some of the decisions that are being made. So what we need, what the city needs, is a leader who can walk in and make some of these progressive decisions," she said.

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"I would hope that Mayor Tory takes a page out of [former New York City mayor Michael] Bloomberg's book, as a mayor, and gets a person in place who is going to lead us in a really positive direction."