There was a time when Curitiba, a city in southern Brazil of 1.7 million inhabitants, was a model town heralding a future of durable development and urbanism.

But that was 20 years ago.

Today, although it features ample green spaces and a public transport system replicated in many other parts of the world, "Curitiba has ceased to innovate," says Jaime Lerner, an architect behind much of the city's layout.

Lerner, who served three terms as Curitiba's mayor from the 1970s to the 1990s, oversaw the creation of numerous parks, an integrated transport system that featured bus stops in the form of tubes, and a recycling system that was advanced for its time.

The former mayor of Curitiba, architect Jaime Lerner, says the Brazilian city -- once at the forefront of durable development -- is no longer innovating / © AFP

In the 1980s, residents learned the basics of sorting their household waste under the slogan "Trash Is Not Trash," becoming among the first in Brazil to do so.

Curitiba also became proud of the fact that 250 cities around the planet sought to copy its public transport system.

"Urban mobility was one of our biggest problems and we were able to put in place a simple system with a solution that matched our reality, without needing to build a subway, as was the trend at the time," said Lerner, who is now 80 years old.

Curitiba's once-innovative public transport system has been copied by 250 cities around the world / © AFP

The tubular bus stops were designed to facilitate passenger access, with raised platforms and ticketing before entering the bus, thus making it almost like hopping onto a subway train.

Special bus-only lanes were also established. That is common in many places today, but wasn't back then -- in Rio de Janeiro, for instance, similar lanes were only set up for the 2016 Olympic Games.

- Changing challenges -

The population of Curitiba has not grown significantly since its innovative heyday. But its suburbs have expanded noticeably, creating new pressures that municipal authorities have not been able to fully tackle.

Curitiba's suburbs have grown exponentially, meaning the public transport system is no longer enough to shuttle commuters to and from work / © AFP

The vaunted recycling program has become obsolete under the weight of new environmental problems, and many of the waterways have become polluted.

Experts especially lament the lack of architectural harmony between the capital and its outlying zones.

In the suburbs, there are virtually no green areas, and the transport system is insufficient to move commuters between the city and their distant homes.

"The vision of dormitory suburbs is completely outdated," said Humberto Carta, a young architect who organized an exhibition last year on how to rethink the urban landscape.

"Public policies need to change, so that they see Curitiba and its suburbs as part of the same thing," said another architect, Luisa Costa de Moraes.

She stressed that most policies put the focus on urban mobility without thinking about alternatives needed to develop suburban centers.

"We are living on past glory and we've simply expanded the model that Lerner brought in," said Carta.

An aerial view of Curitiba's Campo Comprido bus terminal -- the city's public transport system was once the envy of the world but has become outdated / © AFP

He said much of the problem comes from the private sector not investing in property expansion, while public authorities turn a deaf ear to outside ideas.

"If you're not an insider in these halls of power, you can't get a word in," he said.

But for Luiz Fernando Jamur, head of Curitiba's Urban Research and Planning Institute, budget concerns also need to be taken into account -- particularly in a country that has just lived through its worst recession on record.

Lerner, however, rejects the money argument, placing the blame on the "chickenhearted bureaucracy" of the current government.

"They want all the answers before acting. But even if you write a whole thesis on swimming, if you don't jump into the water, it doesn't matter," he said.