Last month, Virginia governor Bob McDonnell proposed dropping the state's tax on gasoline, the revenue from which has become stagnant in recent years.

To make up for axing the state's gas tax, revenue would have to come from elsewhere--extra sales tax, new car registration fees, and a new $100 annual fee for all plug-in and hybrid cars.

As well as vexing owners of hybrid and plug-in vehicles, it's proving unpopular with another group, too--diesel car and truck owners.

Subsequently revised from a complete abolition of gas tax, the new scheme would charge a 3.5 percent wholesale tax on gasoline, but a higher 6 percent tax on diesel.

This works out lower than the current 17.5 cents per gallon tax on gasoline, but a little higher per gallon of diesel--and it penalizes not just truckers, but customers of passenger vehicles and light-duty trucks who've deliberately picked more efficient vehicles.

According to the Diesel Technology Forum, 250,000 drivers would be affected by 2020.

The Forum's Executive Director, Allen Schaeffer, has written a letter to the Virginia House of Delegates to raise the issue--which he says will create an unfair and substantial disparity between gasoline and diesel fuel.

The legislation "directly penalizes Virginians who drive fuel-efficient clean diesel passenger vehicles and is a disincentive to investing in clean diesel cars in the future".

That's something we noted ourselves in our original report, and it's no surprise that others have realized it too.

Schaeffer goes on, "It seems illogical to impose a higher tax at the pump on an increasingly popular technology that is 30 percent more energy efficient and has lower emissions than gasoline, but that is exactly where we’re headed with this plan.

“Diesel fuel is no longer a fuel used only by commercial trucks yet this plan effectively treats it as one and the same, and that price at the pump disparity will discourage consumers from investing in these cleaner more fuel efficient vehicles."

He says the transportation funding package tries to justify diesel's higher rate by the extra damage done to roads by heavy diesel-powered commercial trucks--but 81,000 car and light-duty truck owners will also be affected, and an estimated 250,000 by 2020, if diesel sales continue increasing.

Unintended consequences: Extra oil use, pollution

As well as an unfair disparity between gasoline and diesel prices, Schaeffer cites diesel's efficiency benefits as a reason the plans should be scrapped--20 to 40 percent better fuel efficiency than the equivalent gasoline vehicle, and 10-20 percent lower CO2 emissions.

Such a disparity between gasoline and diesel could tempt buyers back to less efficient gasoline vehicles--wasting millions of extra barrels of oil per year.

In his letter to the House, Schaeffer concludes, "We are concerned that the fuel tax disparity proposed in the final transportation funding package could have the unintended consequence of discouraging the purchase of fuel-efficient clean diesel vehicles that are already reducing fuel consumption and improving air quality throughout Virginia."

Would a greater discrepancy between diesel and gasoline costs tempt you away from diesel cars?

Let us know your thoughts using the comments section below.

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