MIAMI • A pedestrian bridge under construction over a major road in Miami has collapsed, killing at least six people and trapping multiple cars below.
The main span of the 53m walkway was erected just five days earlier in six hours.
The bridge was built to allow pedestrians to safely cross eight lanes of traffic separating the campus of Florida International University (FIU) from the small city where many of the students live. It was scheduled to open next year.
Witnesses told local media the vehicles had stopped at a traffic light when the bridge collapsed on top of them at around 1.30pm local time on Thursday.
Police detective Juan Carlos Llera said: "It sounded like an explosion. A huge bang.
"It looks like a disaster area. It looks literally like a bomb went off."
Ms Isabella Carrasco, who arrived on the scene just after the collapse, told CNN that some cars were completely crushed, and there was "just a lot of debris everywhere".
She saw one woman get out of a car that was "just nicked", and rescue personnel performing cardiopulmonary resuscitation on another person in the street.
After the whole thing broke, I was freaking out. I got out of my car and I and a few other people were sprinting over there. We started helping people whose cars were at least half crushed and whoever was easily saved.
DRIVER LYNNELL COLLINS, who was about to make a right turn when the bridge collapsed.
Another shaken driver, Mr Lynnell Collins, told CNN he was about to make a right turn when "the whole thing really just came down".
He recalled: "After the whole thing broke, I was freaking out.
"I got out of my car and I and a few other people were sprinting over there.
We started helping people whose cars were at least half crushed and whoever was easily saved."
He added: "It's one thing to watch on the news like I always have, and (another thing) to actually be in the situation."
Student Aura Martinez was having lunch in a nearby restaurant with her mother when a waitress told her the bridge had collapsed.
She ran outside and helped pull a woman out of her car, most of which was flattened by the bridge.
"Her car, it was literally a miracle of God. Her car got squished by the bridge from the back, so she was able to get out and she was on the floor and it was just very traumatic," she told the local CBS affiliate.
Student Jonathan Munoz, 21, said he had just driven under the bridge and entered a nearby parking garage when he heard a loud bang.
He thought he had hit something as he looked for a parking spot, so he pulled over and checked his car.
A few minutes later, he got a frantic call from his girlfriend, who had been with him in the car moments earlier.
She was near tears. "Jonathan, the bridge collapsed," she said.
Miami-Dade Fire Rescue division chief Paul Estopinan said at least eight cars were trapped when the 950-tonne concrete bridge suddenly gave way.
Rescue workers, joined by construction workers, desperately dug through the rubble looking and listening for signs of life, using listening devices, fibre optics and dogs.
Officials said they expected the search to continue through the night, and that they had to work carefully because part of the structure was still unsafe.
ABC method to erect bridge
The pedestrian walkway that collapsed onto traffic at Florida International University (FIU) was erected in only six hours using a technique called Accelerated Bridge Construction, according to the school.
Here are a few facts about the project and the ABC technique.
• ABC is a technique in which bridges can be replaced in 48 to 72 hours, reducing planning and work time by years and cutting traffic delays.
• Unlike the conventional method which requires long months of street closures while a structure is being built over a road or river, the parts of the bridge built using the ABC technique are prefabricated away from the site.
• For some bridges, including the one at FIU, the entire length is built before being lowered into place on its supports.
• A national database of ABC projects, which is maintained by FIU, lists more than 100 such projects across the United States.
• The ABC technique uses different methods, designs and materials that are intended to produce safer and more durable bridges with longer service lives than conventional bridges, according to the US Department of Transportation and Federal Highway Administration (FHWA).
• The three leading ABC technologies being promoted under FHWA's Every Day Counts initiative are the Prefabricated Bridge Elements and Systems, the Slide-In Bridge Construction, and the Geosynthetic Reinforced Soil - Integrated Bridge System.
• Funding for the US$14.2 million (S$18.65 million) bridge is part of a US$19.4 million US Department of Transportation grant through the Transportation Investment Generating Economic Recovery programme, according to the university.
• The bridge was the first in the world to be constructed entirely of self-cleaning concrete, said the university. Titanium dioxide used in its construction, when exposed to sunlight, captures air pollutants and keeps the surface white.
Miami-Dade Police Department director Juan Perez said the police homicide bureau would begin investigating as soon as rescue operations ended.
On the FIU website, a time-lapse video shows the intricate raising of the bridge before dawn last Saturday to the accompaniment of triumphant music.
The National Transportation Safety Board also rushed investigators to the scene for an inquiry that was likely to focus on the design and construction of the bridge, as well as the methods used to put it in place.
It was erected using an accelerated modular building method that enabled it to go up in a day.
Bridges made with accelerated techniques are not at more risk of collapse than others, but moving them into place causes different stresses than what the bridges would normally have to withstand, said Mr Andy Herrmann, a former president of the American Society of Civil Engineers.
The US$14.2 million (S$18.65 million) bridge was designed to withstand a Category 5 hurricane, the most dangerous measure by the National Hurricane Centre.
It was built to last 100 years, the university said.
Figg Engineering Group, one of the partners involved in the walkway's construction, said in a statement it was stunned by the collapse and would "fully cooperate with every appropriate authority in reviewing what happened and why".
"In our 40-year history, nothing like this has ever happened before."
Munilla Construction Management, which installed the bridge, also said it would cooperate fully with investigators.
United States President Donald Trump offered on Twitter his prayers for those affected and said his administration was "continuing to monitor the heartbreaking bridge collapse".
The deadliest this century was the 2007 collapse of an eight-lane bridge in Minneapolis, Minnesota, which killed 13 people.
AGENCE FRANCE-PRESSE, NYTIMES, REUTERS
Fears death toll could rise after Miami pedestrian bridge collapses
The Florida authorities continued to search for survivors yesterday after a pedestrian bridge designed to withstand a Category 5 hurricane collapsed and crushed vehicles waiting at a traffic light in Miami on Thursday. At least six people were killed, and officials said the death toll could rise as at least eight vehicles were buried and out of reach beneath the rubble. Uncertainty over the stability of the remaining sections hampered rescue efforts. The main span of the 53m bridge, which connects Florida International University with the city of Sweetwater, was installed last Saturday in just six hours. It was intended to provide a walkway over the busy eight-lane street where a student was killed while crossing last August.