According to a new report from Sightline Institute, drivers in Oregon and Washington State have consistently consumed less gas per capita in every year since 1999. Per capita, Northwestern state residents use less gas now than in any point since 1965---7.4 gallons per person per week, a reduction of more than 25 percent from the 1978 high of 10.1 gallons per person per week.

Moreover, overall gas consumption has remained essentially flat since 1999, despite steady population growth (an additional 1.4 million residents in Washington and Oregon) over the last decade---a period that has included two recessions and one recovery.

According to the report:

The flat-lining of Northwest gasoline sales cannot be attributed to recent economic doldrums; it started long before the current recession began. In fact, it started before oil prices spiked to record highs in 2008; before the US military actions in the Middle East in the last decade; and even before the economic turmoil following the 2001 terrorist attacks. Arguably, it coincides with the beginning of the previous recession, triggered by the “dot.com bust” of 2000.

Similarly, the number of vehicle miles people are traveling (a measure of how much people drive) plateaued in 2002, and has been roughly the same since that year.

The report cites a number of explanations for lower gas consumption, including an aging population (baby boomers now drive less frequently), higher fuel economy standards, economic uncertainty, and increases in density that have shortened commutes and made it easier to take care of household needs close to home.

One implication of Sightline's findings:

The trend has big implications for transportation finance. Oregon and Washington are both considering major bridge, tunnel, and highway megaprojects, and are counting on robust gas tax revenue to help pay for them. Falling gasoline sales and fewer miles traveled could lead to revenue shortfalls, placing transportation finance in jeopardy.

Read the whole report here.