May 6 (UPI) -- An expansion joint on a Pittsburgh bridge had already begun separating before a span collapsed early this year and injured several people, the National Transportation Safety Board said in an update on the investigation. The NTSB said it's reviewed footage taken aboard a transit bus that was approaching before the Fern Hollow Bridge over Frick Park in the city's Point Breeze neighborhood collapsed on Jan. 28. Several vehicles were traveling across the bridge deck when it gave way. Advertisement The 21-ton transit bus had two cameras -- one forward- and one rear-facing -- and both were "determined to have investigative value," the NTSB said in a statement on Thursday. Investigators said that two frames from the video were of particular interest. RELATED Police: Body found in Lake Mead barrel was likely 1970s-80s homicide victim "The first frame is from the forward-facing camera and shows the bridge deck separating at the east expansion joint," the board said. "The second frame is from the curbside camera and shows that, at nearly the same time, the west end of the bridge has already fallen off the west abutment."

May 6 (UPI) -- An expansion joint on a Pittsburgh bridge had already begun separating before a span collapsed early this year and injured several people, the National Transportation Safety Board said in an update on the investigation.

The NTSB said it's reviewed footage taken aboard a transit bus that was approaching before the Fern Hollow Bridge over Frick Park in the city's Point Breeze neighborhood collapsed on Jan. 28. Several vehicles were traveling across the bridge deck when it gave way. Advertisement

The 21-ton transit bus had two cameras -- one forward- and one rear-facing -- and both were "determined to have investigative value," the NTSB said in a statement on Thursday.

Investigators said that two frames from the video were of particular interest. RELATED Police: Body found in Lake Mead barrel was likely 1970s-80s homicide victim

"The first frame is from the forward-facing camera and shows the bridge deck separating at the east expansion joint," the board said. "The second frame is from the curbside camera and shows that, at nearly the same time, the west end of the bridge has already fallen off the west abutment."

NTSB releases investigative update on collapse of Pittsburgh's Fern Hollow bridge: https://t.co/wj5Ai4tPCk pic.twitter.com/XjDyLS9WH2— NTSB Newsroom (@NTSB_Newsroom) May 5, 2022

Investigators said they're also studying structural components that were removed from the wreckage, including the use of 3D laser scanning technology. RELATED U.S. regions with weak gun laws have highest costs from gun injuries

Officials at the NTSB and ​​Federal Highway Administration will conduct mechanical and chemical testing on samples from the bridge's leg and several girder sections. They're also planning to check plate dimensions and the quality of welds on the structure.

The board said in its update on Thursday that the new insights have not yet led to any hard conclusions, but that the evidence hasn't yet indicated any "widespread deficiencies." Investigators are also looking into the bridge's safety ratings, which were reported to be "poor" in recent years.