Jaffa Road has witnessed empires come and go, watched camel caravans give way to stagecoaches and automobiles, seen pilgrims and pioneers, businessmen and bombers. Now change is coming once again to the iconic Jerusalem route.

Supplemented by a network of designated buses and pedestrian malls, a new light-rail train along the city's main thoroughfare will "revolutionize transportation and the city too," said Nadav Meroz, acting director of the Jerusalem Transportation Master Plan.

The rail line, which is making trial runs and will become operational in the summer, has also given Jaffa Road a face-lift.

Until recently, Jaffa Road was one of the most polluted streets in the country. "You couldn't breathe," Meroz said. Now, the sooty gridlock of buses is gone.

From the sleek, shiny train that shimmies up and down the historic street, one can see the roadway's past glory, and present-day decline.

The road, a 1.6-mile stretch running west from the Old City that got its name from the port city it pointed toward, is a timeline of the city's evolution: its history, architecture and people.

Jaffa Road "encapsulates the microcosm of 19th century cosmopolitan Jerusalem," said Nirit Shalev-Khalifa, a historian with Jerusalem's Ben Zvi Institute.

Masons left their mark in the stone walls of the buildings that line the road denoting Jerusalem's emergence from the Old City walls in 1860; ironworkers wrought names into filigreed gates.

In recent decades, upmarket businesses and movie theaters migrated to malls that offered more tasteful shopping, and safer too, as suicide bombings and other attacks plagued downtown. Cheap boutiques, trinket shops and kiosks took over the street, which became a dingy bazaar.

The un-jamming of the city hasn't been a smooth ride. Massive construction projects created a roaming bottleneck that paralyzed the city for years.

The 19th century infrastructure, such as the leaky, and smelly, Ottoman-era terra-cotta sewage pipe had to go. So Jaffa Road got an underground makeover, with top-notch new infrastructure, from sewer lines to fiber-optics "to support another 150 years of development," Meroz said.

Above ground, the makeover is equally ambitious, with much attention and money devoted to just the right street decor, such as benches and lampposts. Facades were cleaned, and 1,000 carefully chosen trees were planted along the train route that includes Jaffa Road.

The street will become "the crown jewel" of a series of pedestrian malls, Meroz promised, "and a beautiful European boulevard."

Meroz said that the project "will serve all of Jerusalem," and that lines are carefully planned to accommodate the various needs of the city's unique social composition, including easing access between the Arab neighborhoods and the main prayer sites and commercial hub of East Jerusalem.

"Leave politics to politicians," said Hussam Watad, director of the community center in the Arab neighborhood of Beit Hanina. "My concern is the daily life of the residents."

Watad said he hopes the project proves relevant to the city's Arab residents, but he has a different problem with the rail line.

He said the track has "stolen" half of the neighborhood's main road connecting it with Jerusalem on one side and the West Bank city of Ramallah on the other, stifling trade and choking the neighborhood.

Beit Hanina desperately needs a bypass road, Watad said.

The road is a rare interest that Beit Hanina shares with the fast-growing ultra-Orthodox Jewish neighborhood of Ramat Shlomo, Watad said.

"We're both applying pressure. God willing, it will work," he said.

Cities need a main street, said Jerusalem architect David Kroyanker, author of "Jaffa Road, Biography of a Street — Story of a City."

Jaffa Road "used to be Jerusalem's beating heart," Kroyanker said. "Now it's a wretched mess of low-end businesses and ugly signs selling whatever for 19.99."

Odel Edri, a 26-year-old mother of two, has seen business in the family shop decline in recent years as construction tore up the street.

"People who want upmarket brands can go to the mall," she said with a shrug.

A few doors down was another dejected shopkeeper.

Sure, it's prettier now, "but pretty doesn't feed a family," said Yakov Levy, a father of four who hopes business will pick up when the light rail starts running this summer. Meanwhile, he's rented out his apartment and moved in with his in-laws.

Through it all, Jaffa Road endures.

One building symbolizes the transformations wrought by history: a Turkish guard post became the elegant home of Noel Moore, a 19th century British consul. The pillars topped by winged lions, sculpted by a 19th century Jewish artist, now guard an Israeli police station.

Sobelman is a news assistant in The Times' Jerusalem bureau.