A man sits on a tram as signs reading 'please don't sit here, respect social distancing ', are displayed on the benches, in Milan, Italy, Wednesday, April 29, 2020. Italian factories, construction sites and wholesale supply businesses can resume activity as soon as they put safety measures into place aimed at containing contagion with COVID-19. (AP Photo/Luca Bruno)

In cities around the world, public transit systems are key to getting workers back on the job and restarting devastated economies, yet everything from trains and buses to ferries and bicycles will have to be re-imagined in the coronavirus era.

In Europe in particular, public transportation is shaping up as a new front line in the battle to tame the outbreak that has killed over 120,000 of its citizens.

In hard-hit Italy, Spain, France and Britain, standing cheek-to-jowl with fellow commuters in packed trains or trams was as much a part of the morning routine in pre-coronavirus times as a steaming shot of espresso or a crispy croissant.

That's going to have to change as authorities try to restart their economies without losing their hard-won gains in controlling the spread of the virus.

Solutions include putting red stickers on the floor to tell bus passengers in Milan how far apart to stand. The Dutch are putting on longer, roomier trains, and many cities, including Berlin, are opening up more lanes to cyclists. In Britain, bus passengers are entering through the middle or rear doors to reduce the risk to the driver.

Announcing a gradual easing of France's strict lockdown, Prime Minister Édouard Philippe called public transit a "key measure for the economic recovery" yet acknowledged concerns among passengers.

A woman walks by signs on the floor showing how far apart one meter is in front of the Saint Lazare railway station during nationwide confinement measures to counter the Covid-19, in Paris, Wednesday, April 29, 2020. France continues to be under an extended stay-at-home order until May 11 in an attempt to slow the spread of the COVID-19 pandemic. (AP Photo/Thibault Camus)

"I understand the apprehension of a good number of our compatriots before taking a metro, a train, a bus, a tram, which are sometimes very densely packed," he said.

When and how to ease restrictions, keep people safe and prevent a second wave of infections is a matter of intense debate around the world.

"There will never be a perfect amount of protection," said Josh Santarpia, a microbiology expert at the University of Nebraska Medical Center who is studying the coronavirus. "It's a personal risk assessment. Everybody has to decide, person by person, what risk they're willing to tolerate."

As restrictions loosen, health authorities will be watching closely for any sign of a resurgence of the virus. Germany has reported an slight uptick in the infection rate since some small businesses were allowed to reopen over a week ago, but authorities said it was too soon to say whether the loosening was to blame.

A residents from the Alexandra township gets tested for COVID-19 , in Johannesburg, Wednesday, April 29, 2020. South Africa will begin a phased easing of its strict lockdown measures on May 1, although confirmed cases of coronavirus continue to increase. (AP Photo/Jerome Delay)

The U.S. on Wednesday learned just how hard the crisis has hammered the world's biggest economy as the Commerce Department estimated that the gross domestic product, the broadest gauge of the economy, shrank at an annual rate of 4.8% in the January-March quarter. That was the sharpest quarterly drop since the Great Recession in 2008-09.

More pain is expected this quarter, as the Congressional Budget Office has estimated GDP will plunge at a 40% annual rate during the three-month period that ends in June.

The United Nations' main labor body raised its prediction of full-time-equivalent job losses in the second quarter to an estimated 305 million.

It also projected that 1.6 billion workers in the "informal economy," including those working without proper contracts or oversight by government regulation, "stand in immediate danger of having their livelihoods destroyed." That is nearly half the global workforce of 3.3 billion people.

A man wears a face mask to protect against the spread of the new coronavirus as he sits on a Metro train, in Paris, Wednesday, April 29, 2020. France continues to be under an extended stay-at-home order until May 11 in an attempt to slow the spread of the COVID-19 pandemic. (AP Photo/Thibault Camus)

In Paris, aircraft maker Airbus reported a first-quarter loss of 481 million euros ($515 million), laid off t housands of workers and sought billions in loans to pull through the crisis.

Ratings agency Fitch cut Italy's government debt rating—the first downgrade to a major economy—in a reflection of the damage done by the lockdowns. The agency lowered the country one notch to BBB-, just one level above junk bond status. It expects the outbreak to shrink the Italian economy by 8% this year.

Germany's economy minister said the government is projecting a contraction of about 11% in GDP by the end of the current quarter. But he also predicted a sharp recovery in 2021.

France, Spain and Greece were the latest countries to announce roadmaps for reopening businesses and schools. They promised to spread people out on trains, trams and buses, and face masks will be the new normal in public.

View of the empty metro station " Temple " during nationwide confinement measures to counter the Covid-19, in Paris, Wednesday, April 29, 2020. France continues to be under an extended stay-at-home order until May 11 in an attempt to slow the spread of the COVID-19 pandemic. (AP Photo/Thibault Camus)

The Dutch national railway began bringing longer trains back into service to make it easier for passengers to stay apart.

The capacity of Milan's metro system will be slashed to just 350,000 passengers a day, compared with 1.3 million on normal workdays. Mayor Giuseppe Sala is calling for staggered working hours and more working from home to help deal with the cutbacks.

Around the world, confirmed infections stood at more than 3.1 million— including 1 million in the U.S.—and the confirmed global death toll topped 217,000, according to a tally by Johns Hopkins University. The true toll is believed to be much higher because of limited testing, differences in counting the dead and concealment by some governments.

With South Koreans about to celebrate their longest holiday since infections there surged in February, authorities urged people to think twice about traveling and to continue to wear masks, not share food and stay home if they are feeling sick.

  • A worker disinfects ticket gates next to a poster about precautions against the new coronavirus at a subway station in Seoul, South Korea, Wednesday, April 29, 2020. The signs read "Recommendation for preventing the new coronavirus infection." (AP Photo/Ahn Young-joon)

  • A woman sits in an empty market in Barcelona, Spain, Wednesday, April 29, 2020 as the lockdown to combat the spread of coronavirus continues. Official statistics show that Spain's unemployment rate rose to 14.4% in the first quarter of 2020, reflecting only the partial impact of the new coronavirus pandemic in Spain's job market. Spain's left-wing coalition government is poised to announce Tuesday further steps to ease the 7-week lockdown, one of the world's strictest. (AP Photo/Emilio Morenatti)

  • A staff worker checks the body temperature of a customer before enter in a supermarket in Madrid, Spain, Spain, Wednesday, April 29, 2020 as the lockdown to combat the spread of coronavirus continues. Official statistics show that Spain's unemployment rate rose to 14.4% in the first quarter of 2020, reflecting only the partial impact of the new coronavirus pandemic in Spain's job market. Spain's left-wing coalition government is poised to announce Tuesday further steps to ease the 7-week lockdown, one of the world's strictest. (AP Photo/Manu Fernandez)

  • Residents from the Alexandra township in Johannesburg gather in a stadium to be tested for COVID-19 Wednesday, April 29, 2020. South Africa will begin a phased easing of its strict lockdown measures on May 1, although confirmed cases of coronavirus continue to increase. ((AP Photo/Jerome Delay)

  • A woman wears a face mask to protect against the coronavirus as she passes a closed shop in London, Wednesday, April 29, 2020. The Scottish Government is recommending the use of masks in shops and public transport, and Mayor of London Sadiq Khan has called for people to wear facemasks, while the British government has refused to recommend the face covering. (AP Photo/Kirsty Wigglesworth)

  • A policeman, wearing a mask, walks past murals during lockdown in Kohima, capital of the northeastern Indian state of Nagaland, Wednesday, April 29, 2020. Prime Minister Narendra Modi imposed a three-week lockdown on March 25 and later extended it by 19 days until May 3, when he is scheduled to address the nation on radio and television. His government has allowed a partial resumption of manufacturing and farming in rural areas and reopenings of neighborhood shops selling both essential and non-essential goods. (AP Photo/Yirmiyan Arthur)

  • A passenger walks at an empty domestic terminal of Haneda Airport in Tokyo, at the start of Golden Week holiday Wednesday, April 29, 2020. Japan's Prime Minister Shinzo Abe expanded a state of emergency to all of Japan from just Tokyo and other urban areas as the virus continues to spread. (AP Photo/Eugene Hoshiko)

  • A worker disinfects the restaurant area of the roof terrace of the Atlantic hotel, in Rome, Wednesday, April 29, 2020. After seven weeks in lockdown to contain one of the world's worst outbreaks of COVID-19, Italians are regaining some freedoms, starting on May 4, public parks and gardens will re-open and people will be able to visit relatives who live in the same region. (AP Photo/Andrew Medichini)

  • A man runs on an empty street next to a shop offering face masks for sale amid concerns over the country's coronavirus outbreak on Israel's 72nd Independence Day, in Tel Aviv, Israel, Wednesday, April 29, 2020. The Israeli government announced a complete lockdown over their Independence Day to control the country's coronavirus outbreak. (AP Photo/Oded Balilty)

  • A sign outside the Roxy Theater on the Sunset Strip thanks frontline workers, Tuesday, April 28, 2020, in Los Angeles. California Gov. Gavin Newsom laid out a four-stage plan Tuesday to reopen businesses, schools and entertainment events. The governor said California is currently in phase one. As the state sees hospitalization rates for the coronavirus stabilize, officials plan to move into phase two in the next few weeks, allowing some retail stores to get back to business. (AP Photo/Marcio Jose Sanchez)

  • Tobacco auctioneers wear face masks to protect against coronavirus while inspecting crop on the first day of the tobacco marketing season in Harare, Zimbabwe, Wednesday, April 29, 2020. The tobacco selling season began across the country with auction floors complying with strict Covid-19 measures which included setting up clinics and isolation sites. (AP Photo/Tsvangirayi Mukwazhi)

"We must not let a moment of carelessness trigger mass transmissions that would make the efforts we invested so far vanish like bubbles of water," Vice Health Minister Kim Gang-lip said.

In China, where the virus first emerged late last year, the government announced that its ceremonial parliament will be held late next month after its original meeting was postponed. The convening of the full session will involve 3,000 members.

In Japan, officials asked people not to travel during the country's upcoming Golden Week holiday.