DENVER -- Hundreds, possibly thousands, of the nation's box girder bridges, have wood construction forms still inside. Experts say those forms could accelerate corrosion and prevent the complete visual inspection of a bridge's interior.

The Colorado Department of Transportation insists the bridges are safe for drivers, but is now removing or preparing to remove forms from at least eight bridges in the metro area, most over Interstates 25 and 70.

In May, a CALL7 Investigation raised questions about wood forms left in bridges after combing through CDOT files and finding written warnings from bridge inspectors concerned about the hidden danger.

Notes and memos read, "The formwork keeps bridge inspectors from being able to properly inspect bridges creating a potential safety hazard," and "We are feeling uncomfortable as to what we might be missing during our routine inspections."

"Well I think you guys raised many many questions and some things we want to look at," said CDOT spokesperson Stacey Stegman.

The issue specifically affects a style of bridge known as a box girder. It's a hollow concrete box set on pillars to support the deck and roadway of a bridge. When building the bridge wet concrete is held in place by wood forms. Steel rods and crossbeams are used to reinforce the girder. Once the concrete hardens, the wood forms should have been removed allowing for easier access for inspectors.

The CALL7 Investigators found the forms were left behind in nearly a dozen high traffic bridges in the Denver area.

Stegman said, "Our maintenance crews have identified four separate structures. They have removed the forms out of one and are in the process of removing forms out of the other three."

She went on to say that contractors would be hired to remove forms from four more bridges, but stressed it is a very low priority for the department and unnecessary for inspections.

CALL7 Investigator John Ferrugia asked Stegman, "If it's not necessary, taxpayers are going to be asking, why are you spending $500,000 to do it?"

"That's a good question and that is why we haven't identified a plan to remove them out of [all the bridges] yet," said Stegman.

But the Federal Highway Administration and local experts told 7NEWS, removing wood forms from box girders should be a higher priority.

In May, a CALL7 Investigation showed how wood forms left in place can trap moisture and, possibly, accelerate bridge corrosion.

"We're looking for distresses prior to having any kind of a structure falling down," said Dr. Kevin Rens, chair of the Civil Engineering Department for the University of Colorado at Denver.

Rens studies bridge deterioration.

"When we get to look at a structure at an early stage of deterioration rather than when we see it in a late stage of deterioration, often the cost to the general public is going to be much smaller," said Rens.

The CALL7 Investigators learned there has never been a nationwide audit of box girder bridges to determine how many still have wood forms inside, so CALL7 sent Open Records Requests to each state department of transportation asking if their state had box girder bridges and, if so, how many still had wood forms inside.

Thirty-five states responded to 7NEWS' request for information. Some had none or just a few box girder bridges with forms inside, but others like Kansas and Nevada listed hundreds.

The Federal Highway Administration told 7NEWS, this issue affects a small fraction of bridges nationwide and they do not believe it is a critical safety issue for drivers, but the agency wants states to take the issue seriously.

In a statement to 7NEWS, Cathy St. Denis of the Federal Highway Administration wrote, ""The Federal Highway Administration places public safety as its top priority. We will continue to work with state departments of transportation to ensure that bridges across the nation, and the professionals who inspect them, remain safe. Our commitment to safety and thorough bridge inspections has never been stronger. Access is often provided to the interior of box girders to provide for more thorough inspections and evaluations, as well as to facilitate maintenance activities. For the safety of the inspectors and maintenance staff, providing an environment that is free from hazards is important, as is providing an unobstructed view of the interior portions of the girders."

"We need to be able to get into the structure to look at it, so receiving some of that pressure from the top level administration for bridges is going to help open the eyes for other states I think," said Rens.

One more note, the CALL7 Investigators obtained e-mails between CDOT or other state departments of transportation indicating CDOT had serious concerns about the 7NEWS investigation and, at times, tried to coordinate with other states and industry groups in their responses to us.

A mass email from Stegman to other departments of transportation read, "All - Please accept my apologies for Colorado's aggressive reporter and his open records request. I know these are time consuming and we're all very busy. As background, here's how we responded to this issue.(Attached was Stegman's response to 7NEWS initial report in May) I would very much appreciate it if you would keep me in the loop on your response to him."

Stegman also sent an e-mail to a transportation official in Tennessee, whom 7NEWS was coordinating an interview. Stegman told the Tennessee official, "I wanted our bridge guy to touch base with yours as he mentioned to me the issues you shared may not be the same as ours. I thought it would be good if he could clarify ours so we're providing an apples to apples comparison for them."

Tony Dorsey, the manager of media relations for the American Association of State Highway and Transportation Organizations also wrote to all state departments of transportation saying,” In an effort to shield you from contact with the reporter I agreed to email you a list of questions about box girder or wood form bridges that he wanted answers to."

The e-mail continued, "Despite our best efforts KMGH is proceeding with its probe."

Another e-mail from Dorsey reads, "If you or someone from your department receives a call from this reporter(sic) or his producer... --please feel free to refer him directly to me. I would like to shield you and your department from any unnecessary harm."

In a phone conversation Dorsey told 7NEWS, AASHTO does not believe wood forms left in bridges is a public safety issue.

Other experts, who have spoken to 7NEWS on the issue, disagree.