Diesel fuel prices - have they been dropping?

A lot of the price differences between diesel and gas have little to do with the actual cost of production. In many states, diesel is taxed at a much higher rate than gas. The justification often offered up is that most diesel is burned by heavy trucks that cause more wear and tear on the roads, so it is appropriate that they pay more in taxes for road repair. In actuality, I suspect that it is simply a matter of political expediency as a higher tax on diesel would make fewer voters angry. In the last fuel tax go-round in Indiana for example, diesel ended up being taxed at something like $.50/gallon higher than gas.