The rising price of gas is having a profound effect on the highways, both good and bad.

The good news: Traffic deaths around the country are plummeting, just as they did during the Arab oil embargo three decades ago.

The bad news: Less gas being consumed means gas tax collections are declining, which means there is less money to fix highways.

Researchers with the National Safety Council report a 9 percent drop in motor vehicle deaths overall through May, compared with the first five months of 2007, including a drop of 18 percent in March and 14 percent in April.

Preliminary figures obtained by the Associated Press show that some states have reported declines of 20 percent or more. Thirty-one states have seen declines of at least 10 percent, and eight states have reported an increase, according to the council. The federal government reported in April that miles traveled fell 1.8 percent in April, compared with a year earlier, continuing a trend that began in November.

The last time road deaths fell this fast and this sharply was during the Arab oil embargo in 1973-1974, when fatalities tumbled 17 percent, from about 55,100 to 46,000; and as states raised the drinking age to 21 in 1982-83, when fatalities fell 11 percent, from roughly 49,300 to 44,000.

But the reduction in driving and the move to more fuel-efficient cars are hitting Uncle Sam in the wallet. The federal highway trust fund could be in the red by as much as $3.2 billion or more next year.

The fund, due to finance about $40 billion in transportation projects next year, has become increasingly strained. But the problem has taken on greater urgency as lawmakers face a backlog of projects to maintain the nation's aging interstate highway system and ease traffic congestion.

"The situation has only been exacerbated by rising fuel prices, which are causing motorists to drive less and resulting in less revenue for transportation improvements," David Bauer, senior vice president for government affairs at the American Road & Transportation Builders Association, told the Los Angeles Times.

In the short run, lawmakers are scrambling to figure out how to close the funding gap. Federal highway spending nationwide could be cut by one-third beginning Oct. 1, according to the American Road and Transportation Builders Association.

In the long run, lawmakers must figure out whether the 18.4-cent-a-gallon federal gasoline tax, which helped bring in money when fuel-hungry SUVs were hot, is still a viable way to fund transportation projects amid heightened concern about gasoline prices, U.S. dependence on foreign oil and global warming.