Part 1 of a series. Here are Parts 2, 3 and 4.

Este reporte tambien está disponible en español.

The solution to Boston's transportation woes may be south of the border.

Mexico City has transformed its roadways over the last 15 years with a faster, more efficient bus system known as bus rapid transit. They call it Metrobús. And it could be a model for Boston.

An estimated 21 million people move through Mexico City's metro area every day. And that means traffic — lots of it. Car horns echo through the streets during rush hour.

Metrobús allows residents to avoid that headache.

The buses cruise down their own lanes in the middle of the road. They stop next to a platform like a subway, so riders walk right on without having to take a step up. This makes boarding quick and easy — especially for people with disabilities. And just like a subway, you pay as you enter the bus station, another feature that speeds up boarding.

These are all elements of bus rapid transit. And you can't miss it in Mexico City. The bright red buses fly past car traffic — sometimes only a minute apart.

"Here comes another one," Zara Snapp calls out. She's a 36-year-old drug policy consultant who uses Metrobús often to get to appointments.

"You know I look at people who are sitting in their car in traffic and I just think, 'What? Why? How do you even — how do you handle that?' Like I would get so impatient," Snapp says.

Snapp catches a Metrobús downtown. It's about 5:30 p.m. on a Thursday, and she needs to get to a meeting along Paseo de la Reforma, the city's iconic tree-lined boulevard. It's dotted with monuments and cuts through the heart of Mexico City.

The busy roadway also has the city's seventh and newest Metrobús line.

"I think it's definitely a more convenient option a lot of the time than taking other forms of transportation," Snapp says. "It's just an easier way to get around the city."

So much easier that a lot of people are using it. Metrobús moves 1.5 million people every day - more than the entire MBTA moves daily - and many riders here say they love it.

Buses are packed during rush hour, and sometimes there are long lines at stations. (Keith Dannemiller for WBUR)

"Metrobús is really, really, really useful for people like me that use it every day for work," says Javier Paz.

Paz just got off work at his human resources job downtown and is ready to catch a Metrobús along Avenida de los Insurgentes, a major avenue that runs north to south across Mexico City. This is where the city first launched bus rapid transit in 2005.

"It's a matter of economy too because six pesos for a ride to south, to north of the city, it's great," Paz adds.

Six pesos for a Metrobús ride translates to about 30 cents. That is great for many commuters. But the system also has its challenges. Buses are packed during rush hour, and sometimes there are long lines at stations.

Fernando Suarez, a financial analyst, waits for friends at a Metrobús stop on Insurgentes. He likes the service but says the buses are too crowded to get on sometimes.

"What I feel is that we need more Metrobúses for so many people that are here," Suarez says, speaking in Spanish. "I think it makes it easy for everyone to get home or to work, but I do not think there are enough Metrobúses."

Many riders agree. Transportation officials in Mexico City want to expand Metrobús. They see the system as a victim of its own success.

A map of the various Metrobús routes. Route 1 extends south to El Caminero. (Courtesy Metrobús)

Mexico City first turned to bus rapid transit, or BRT, because of its traffic congestion. It also had a serious pollution problem.

"Being in Mexico City was [like] being poisoned," says Ulises Navarro, a BRT expert and transportation engineer.

He says 20 years ago no one would recommend going to Mexico City because the pollution was so bad.

"And then the BRT became, 'Oh, this here is something that is cheap to implement.' It's not real expensive to implement as metro. And at the same time will help us to alleviate the greenhouse [gas] emissions," Navarro says.

Metrobús uses low-emission buses that can carry up to 240 riders. Navarro says the system has taken more cars off the road than any of the city's other transit options — like the metro (subway), bike share and trolley system. According to Navarro, 70% of Metrobús riders used cars before the system was put in place.

In terms of expense, building a subway line would cost 20 times more than bus rapid transit, according to Metrobús.

Air pollution creates a haze over Mexico City on May 20, 2018. (Marco Ugarte/AP)

Massachusetts transit officials and advocates hope to see their own success with bus rapid transit.

Boston and other surrounding communities have tested bus-only lanes and other elements of BRT, such as traffic lights that stay green for buses. Some of the bus lanes have become permanent. Everett has even installed platforms at some stops to ease boarding. So far, dedicated bus lanes in the region have made rides faster, according to local officials. And more bus lanes are on the way.

Snapp, the drug policy consultant in Mexico City, has some thoughts on BRT in Boston as she gets off at her Metrobús stop along Paseo de la Reforma. She knows a bit about Boston because she was a graduate student at Harvard.

"I realize that in the center of the city it's tough because there's small, horse-drawn carriage streets," Snapp says with a laugh. "But we also know that people are coming from Newton and all these other little cities all around to come into Boston and work. And so that would be the opportunity I think."

WATCH: Zeninjor Enwemeka's Instagram Story as she reports about the Metrobús.