The Colorado Department of Transportation now estimates that about $50 million – nearly half of what the feds took back from Colorado last week when they rescinded $8.7 billion in highway funds nationwide – will come from road projects already funded.

They will now have to be deferred, CDOT spokeswoman Stacey Stegman said.

The list of projects to be affected isn’t assembled yet. They had not gone to bid or contract, Stegman said, because CDOT saw the rescission coming earlier this year and held back on awards.

But not enough for the size of it. The Federal Highway Administration ended up rescinding $114.9 million in aid from Colorado – including getting dinged an extra $689,648 because Nevada didn’t have enough unspent federal funds to return its full share. All states are picking up extra payback to make up for Nevada.

The FHWA put out an FAQ explainer outlining the issues involved in the rescission, its legal basis and detailing how it would proceed. You can read that FAQ here.

Colorado’s loss of federal funding for projects already on the funded list comes in part because the state spent all of its federal allocation in some categories of aid from which FHWA wanted money back. But Stegman said all of the givebacks will be covered by unspent federal aid authorizations, and no state funds are involved. Inside Lane reported this week that because of the state had spent more in some categories and didn’t have enough left to return to the FHWA, it might have to dip into state funds.

But the FHWA is adjusting the deficits and surpluses across various categories to make up differences.

“We had sufficient unobligated balances to comply with the rescission as a whole, however, a preliminary review of our some of our accounts shows we lost unobligated balances that were programmed in the STIP or projects that were already budgeted but not obligated in projects,” Mickey Ferrell, federal liaison in CDOT’s Office of Policy and Government Relations, wrote in a memo updating the situation on Thursday.

The STIP is the State Transportation Improvement Program. A project gets on the STIP after the state has identified the funding for it. A project cannot be done unless it gets on the STIP. You can read the current STIP report here. It is updated daily.

“Again, based on preliminary analysis, we have estimated the rescission will have impacted approximately $50 million in ‘real’ dollars. ‘Real’ dollars refers to dollars that could have or have been programmed in projects but now cannot go forward because there is no apportionment.”

The nationwide rescission is following a strict formula set up in the law requiring specific amounts from all the various categories of aid.

For example, FWHA wanted $22.95 million back from CDOT in the Interstate Highway Maintenance category and $30.78 million from National Highway System funds. But with maintenance a high priority for CDOT, it had already spent those categories to the extent that it is now giving back zero in the Interstate Highway Maintenance category and just 92 cents in the National Highway System column.

To make up the difference, CDOT is surrendering more money in some vital areas that fund big construction projects. CDOT has to give up $45.49 million in the category called Congestion Mitigation/Air Quality. That’s the federal aid category from which many highway widening, traffic congestion projects are funded, especially in metro Denver. And it’s $36.1 million more than the initial FHWA rescission of $9.4 million in that category.

That means trimming a number of projects that were ready to go.

And it is giving back $14 million in urban-area Surface Transportation Program funds for areas over 200,000 population, instead of the $10.1 million FHWA initially wanted. On the other hand, because the state already had obligated all STP funds for areas under 200,000 population, it can give back only $2.83 – that’s two dollars and 83 cents; I didn’t leave off “million” or anything – instead of the $15.96 million FHWA initially listed.

While it already sounds complicated, the math gets worse.

The FHWA by law must rescind specific amounts from specific categories nationwide, meaning it’s not only necessary for each state to come up with its bottom line figure to give back, but the nationwide totals in each category must match a specific amount. For every state that has a shortfall in Interstate Highway Maintenance, such as Colorado, other states have to give up more in that category.

“We did not get a choice in how the dollars were taken,” Ferrell told Inside Lane. “You use a great example of why this rescission was so difficult. Interstate Maintenance is a good example. CDOT had $0 left. Meaning other states had to ‘make up’ for our lack of funds in that category.

“ The converse is true as well in other categories where we had to make up for other states. Literally, account by account across all funding categories.

“It is the most complicated budget action I have ever seen.”