The government’s combined receipts from all excise taxes in the Highway Trust Fund showed no growth in the federal fiscal year that ended Sept. 30, the Treasury reported, as a large decline in retail taxes on commercial trucks more than offset mild gains from fuel taxes.

In its monthly statement for September, the final month of the fiscal year, the Treasury said total HTF excise tax receipts net of refunds were $41.127 billion for the past 12 months, down 0.5 percent or almost unchanged from $41.344 billion in the 2016 fiscal year.

A look at separate Treasury reports on the various Highway Trust Fund contributions for the last two fiscal years showed that gasoline tax receipts of nearly $26.604 billion in the year through September were up 1.8 percent from the previous year, while diesel taxes generated about $10.736 billion for a 4.6 percent increase.

The combined 2017 increase in receipts from taxes on both gasoline and diesel plus related fuels was about $941 million, for a 2.6 percent gain, the Treasury reports showed.

However, revenue from retail truck taxes for the trust fund reached only $3.117 billion in fiscal 2017, down by 27 percent or $1.148 billion for a drop that was more than enough to offset the relatively small gains from motor fuel user fees.

Those numbers reflect the volatility that stems from such revenue streams as equipment sales, which can fluctuate sharply based on market demand or changes in interest rates for high-cost purchases.

Joung Lee, policy director for the American Association of State Highway and Transportation Officials, told the AASHTO Journal that the 2017 excise tax receipts help explain why industry groups are urging Congress to find ways to add dedicated revenues to the trust fund.

“Congress and the nation cannot depend on the trust fund’s current mix of fees to even keep growing year to year, depending on market conditions,” Lee said, “and it continues to generate far less than Congress has authorized the trust fund to spend. That means the current $13 billion funding gap will widen to $23 billion by 2027 unless lawmakers address this structural problem.”

AASHTO has also provided Congress with a wide-ranging list of potential revenue-raising options that could put the trust fund on a sustainable path.

The trends in excise tax receipts for the trust fund could also soon worsen as fuel-stingy vehicles make up a greater proportion of the national fleet.

And operators of freight-hauling truck fleets are eyeing the possibility of operating over-the-road trucks in electronically connected platoons with one or more other trucks to cut their fuel usage.

An Oct. 22 Washington Post story said a truck-matching database could have such platoons operating on highways in states that allow them as soon as 2018, a development that could curb future increases in diesel tax collections for the trust fund. (See related story in Nation section.)