The Alamo City is expected to grow by more than 1 million people by the year 2040, but how is the city preparing for this rapid explosion of growth that's just getting started?

"San Antonio is about 500 square miles. We are growing. We have a lot of unique neighborhoods, historic neighborhoods, so we want to make sure we preserve these neighborhoods and accommodate that growth," said Bridgett White, the city's director of the planning department.

While 2040 may be 23 years away, the city is already preparing for growth by putting three plans in place.

The first is the "comprehensive plan."

"The comprehensive plan is a policy document for the city," White said.

It is a long-term plan for future growth, development, land use, infrastructure, and services that breaks the city into 13 regional centers.

"Each of the 13 centers are quite different, so we have to make sure that we plan for areas throughout the community to identify," said White, noting that they'd be areas of stability and areas of change. "We look at housing, transportation, the environment, and military given that San Antonio has that unique military component."

In 1950, San Antonio was a much smaller city than it is now, with only a little more than 400,000 people. In the 2000 census, San Antonio's population crossed the 1 million mark.

Between 2000 and now, the city's growth expanded rapidly with the focus of new construction on the northwest, north, and northeast sides, pushing the population close to 1.7 million.

City planners say that by the year 2040, the focus of the growth will shift from the outskirts of the city back to downtown, with the population closing in on 3 million people.

How will all those people get around? That's where the multi-modal transportation plan comes in.

"Here in Texas about 95 percent of us drive our own vehicle to work every day," said Art Reinhardt, director of transportation and capital improvements.

"We can't build enough roadway to handle all of the cars that will be here by 2040. It'll just be a major parking lot," said Doug Melnick, the city's chief sustainability officer.

The solution also requires a change in mindset to get people out of their cars and into better inter-working infrastructure.

"If mass transit was more convenient, I could ride my bike to the bus stop, put it on the bus and bring it down," Reinhardt said.

This could also make mass transit safer, like the Vision Zero plan enacted in 2015 to cut down on pedestrian fatalities.

"Taking that driver error out. Self-driving vehicles are something we are looking at as well," Reinhardt said.

Cutting down on cars also cuts back pollution, which relates directly to the third plan: sustainability.

"[That includes] issues such as air quality, water quality, water security, food security, climate change, and resilience," Melnick said.

Water is a key element in climate change and a big deal in South Texas. And it isn't just about water conservation.

"What hits the ground in a rain event. What flows into our streams. What gets recaptured into our aquifer. Those are all things we need to continue to work on," Melnick said.

With three big plans already in the works, both Phoenix and San Antonio are projected to pass Philadelphia in population in about 20 years and battle it out for the fifth-largest city in the U.S.