When Boston’s transit authority increased the subway fare by a nickel in 1949, two women wrote a protest song.

When São Paulo’s bus service announced a nine-cent fare hike three weeks ago, Brazilians took to the streets against it. The protests have only grown larger since, with more than a million participants in 100 cities across the country demonstrating yesterday.

As many observers have noted, the cost of a bus ride isn’t really the fundamental issue at stake for many of the protesters as much as the country’s profound inequality more generally.

But what risks being lost in the accompanying discussion of Brazil’s future is, ironically, the very question that sparked them in the first place: how much should public transport cost?

It’s not a trivial problem, even now that the government says it no longer plans to raise the bus fare. In fact, the way Paulistanos move about their city encapsulates many of the deeply rooted inequalities in Brazilian society that the country’s leaders have now been forced to confront.

At $1.46, the new fare would have been a bit lower than what most American transit riders pay. But in a country where the minimum wage is just $1.60 per hour, even a rise that small packs a punch. A São Paulo resident making minimum wage who takes 12 bus rides a week would devote about a quarter of his annual income to transport.

That’s a staggering percentage compared to other cities with well-used transit systems. By contrast, a New Yorker making minimum wage pays 9 percent of his earnings toward subway fare; a Parisian, 4 percent.

There’s no single root cause of this discrepancy, but there are a few factors that help explain it.

First is the continued prevalence of Brazil’s “informal economy,” the unregulated, cash-under-the-table industries that employ 55 percent of Brazilians, according to one estimate. This economic reality causes many Paulistanos to slip through the cracks of the existing employer-subsidy program, which caps the amount a worker can pay for bus fare at 7 percent of his income.

Then there is the fact that almost all riders on the São Paulo buses pay the same flat fare, whether they’re commuters taking two trips per day or visitors taking two per year (students get a discount, and the disabled and elderly ride for free).

It’s a vastly different system from the one most other cities have adopted, where different options are offered for frequent and infrequent riders, the latter effectively subsidizing the former. A New Yorker with a monthly pass who takes 12 trips every week, for example, will pay 20 percent less per ride over the course of a year than a tourist with a single-ride ticket.

In fact, the protests have come just as São Paulo is preparing to introduce a similar system, which had been a campaign promise of Mayor Fernando Haddad.

But Paulistanos wishing to register will have to do so online, an issue in a country where internet access varies widely by socioeconomic class. And the new monthly bus pass won’t work on the city’s metro train system—the 12th-busiest in the world—though officials say they are studying the option.

Why has São Paulo taken so long? The reason isn’t technological—a smart-card system has been in place for nearly ten years. Instead, it’s the recurring theme of Brazilian politicians ignoring the transport needs of their poorest constituents. Hardly surprising, given that it’s a city where the wealthiest have taken to avoiding street-level travel entirely by using helicopters.

The flat fare may be the most immediate example of this, but it’s endemic in many ways to the manner Brazil goes about funding public transit.

While state-run banks invest hundreds of millions of dollars in new stadia for the upcoming World Cup and Olympics, very little federal or municipal money is provided for trains and buses. In fact, rather than receiving heavy state subsidies as most American and European transit networks do, São Paulo’s bus system is actually taxed by the government. This levy is passed on to the riders, comprising about 9 percent of the total bus fare, according to a 2011 report.

It’s an extremely regressive set-up, one that helps explain why Brazil’s lower classes are paying first-world bus fares on third-world salaries. And though the São Paulo government agreed to cancel the fare hike, it shows that the problems facing public transit in Brazil are far more deeply ingrained in questions of social class.

Still, there have been definite improvements. One overlooked fact is that Paulistanos making minimum wage would have actually paid a lower percentage of their income toward transport this year than they did last year, even with the fare increase. The reason: Brazil’s annual wage adjustment, which increased the minimum salary this year by $300. It’s a testament to the progress Brazil has made in reducing inequality—the minimum wage has more than quadrupled since 2000–but also an indicator of just how unequal Brazilian society was to begin with.

Brazil’s economic boom has been a socioeconomic leveller as far as transport is concerned in other ways, too—and not always positive ones. A government report found that while commute times for everyone in São Paulo had risen dramatically since the 1990s, the gap between rich and poor in time spent commuting actually decreased.

In fact, if traffic gets so bad that middle- and upper-class Paulistanos start to abandontheir city’s entrenched car culture, it might finally goad the government into investing more heavily in public transport.

There’s some evidence that this is happening already. The percentage of trips in São Paulo made by car declined from 2002 to 2007, according to a London School of Economics report. Several new metro lines are planned, and a recent proposal called for 68 miles of new express bus lanes in São Paulo by 2025, in the hope that the promise of a faster commute will persuade would-be motorists to take the bus instead.

But with only 46 miles of metro lines for an urban area with more people than Florida, reducing inequality may well demand more of a fundamental change in how São Paulo residents see the role of public transit in their city’s future.

Until Brazil figures out how to reduce its massive income inequality, it seems likely Paulistanos will continue to take to the streets, no matter how much a bus ticket costs.