Late last week, the nonpartisan Congressional Budget Office (CBO) released its preliminary score of the House’s BUILD America 250 surface transportation reauthorization bill. The tantalizingly incomplete document indicates that, even with the addition of the new federal registration fees on electric vehicles and plug-in hybrids, the combination of the preexisting Highway Trust Fund fiscal imbalance and the spending increases provided by “BA250” would necessitate an additional $150 billion in Trust Fund deposits from somewhere (presumably the General Fund) in order to keep the Trust Fund from running out of money prior to the end of the bill’s reauthorization period on September 30, 2031.

Actually, CBO has done two separate things lately.

First – New Baseline. While there was no public announcement, last month CBO updated the spending side of its annual budget baseline, an earlier version of which was issued in February 2026. That earlier baseline was “locked” a few weeks prior to release, at a point before the enactment of the annual fiscal 2026 appropriations acts on January 23 and February 3. This meant that the starting point used for the spending side of the February baseline was not the fiscal 2026 enacted levels but the 2025 levels carried over from the continuing resolution then in effect.

The new June baseline adjusts all discretionary accounts to use the enacted 2026 appropriations levels as starting points. For Highway Trust Fund accounts, this increases every year’s new obligation levels by around $1.8 billion per year over a decade. CBO then updated their Highway Trust Fund forecast in June to reflect increased outlays caused by the actual increase in 2026 spending levels, carried forward with inflation for a decade. CBO says this increased outlays by $10.1 billion over five years, and the change in balances also had a minute effect on interest earned. The total cash shortfall at the end of the five-year reauthorization period went from $121 billion to $131 billion because of this baseline adjustment.

Second – Score of BA250. Then, on July 9, CBO issued its “Estimated Effects of Selected Provisions of H.R. 8870, the BUILD America 250 Act.” This document used the June CBO baseline as a starting point – updated spending assumptions, but the same revenue assumptions as the earlier February baseline. Then the spending increases in the “BA250” bill were added on top. Table 1 in the CBO document only goes five years (to the end of 2031) and not ten years like a baseline projection, but it adds an additional $16.4 billion in cash outlays to the earlier baseline projection.

At this point, the CBO estimate discusses the federal registration fee on electric and plug-in hybrid vehicles levied by section 1129 of H.R. 8870. As reported from the Transportation and Infrastructure Committee, H.R. 8870 does not direct that the receipts from those fees be deposited in the Highway Trust Fund. (The T&I Committee is, in fact, forbidden from doing so, because the Trust Fund is the exclusive preserve of the House Ways and Means Committee, which has not acted upon H.R. 8870 yet.)

As a result, Table 2 in the CBO estimate states that the fees would bring in $2.8 billion over five years and $12.4 billion over a decade on a net basis, after the payroll-excise reduction has been made. (Every tax on a paycheck, or every excise tax on a good or service (or tariff on the same), takes money out of the hands of a person or company and keeps it for the government. That means that someone, somewhere, has a little less income and thus pays a little less income tax. CBO has to take this relationship into account when estimating the proceeds of new taxes and fees – the increase in tax or fee receipts is partially offset by a reduction in federal income tax receipts.)

If a payroll or excise tax increase is devoted to a trust fund account, the trust fund gets credit for the gross amount raised, not the amount after the income tax offset. CBO says that the gross amount of the EV fees is around $17 billion over a decade. We were able to get the five-year totals and they are $3.8 billion over that period – not enough to offset the $16.4 billion in spending increases under the bill.

Bottom Line: $150 Billion Needed. The nutshell summary is: in addition to extending the existing taxes, extending the life of the Trust Fund, and depositing the new EV registration fees into the Highway Trust Fund, the Ways and Means Committee must also provide almost $150 billion in extra Trust Fund deposits in order to keep the Trust Fund solvent through the end of fiscal year 2031. The total amount of negative shortfall is $143.9 billion; a standard $4 billion end-of-year cash cushion in the Highway Account and $1 billion in the Mass Transit Account would bring it to $148.9 billion, but rounding up to $150 billion is safer.

Ways and Means could lower this a bit via calculation of how much interest a $100+ billion transfer would earn while being held in the Trust Fund until spendout. (This was an unforeseen aspect of the IIJA – the $118 billion bailout transfer provided by that law wound up bringing in close to $20 billion in interest over the 2022-2026 period when almost none was anticipated at the time. It all depends on interest rates, which depend on the central bank, whose decisions depend on inflation and other concerns.)

But that level of transfer is only necessary if the House decides to pass the full five-year bill. In order to figure out what would be needed for a short-term extension, one must look back at the new CBO baseline. The updated projections estimate that, under current spending and tax levels, the Mass Transit Account will run dry first, sometime in late summer 2027. (The month-by-month spending logs for the Trust Fund for the last few years show Mass Transit Account outlays very back-ended, with over 20 percent of annual outlays occurring in September for the last two years.)

If Congress were to pass a one-year extension of the IIJA at fiscal 2026 spending levels, the extension would also need an additional transfer of about $4 billion into the Mass Transit Account to keep it solvent for that period of time. The latest baseline projects the Highway Account to end FY 2027 with a positive balance of $13 billion, which should be a good enough safety margin to get through the year.

Here is our representation of the new HTF baseline and the CBO score of the various changes made by the BUILD America 250 Act.