The problem with JeffMeden's theory is that gas doesn't follow traditional market analysis, seeing how the demand/supply/price of fuel doesn't really change, and doesn't really have a direct affect on each other.
-edit: the price is the only part of that equation that really changes, but it has very little bearing on the other two parts.
Consider, the price of a barrel of oil dropped over $25 in the last few weeks. Why? Well, demand is down slightly, from last year, but it's still about what it was last month. No affect.
Supply is bad right now, some Shell pipelines got blown up by some assholes in south america this month. Typically, this lack of supply should drive up prices, right? Not this time.
So where does the price actually come from, since those two things really have no bearing on it? Oh, that's right, asshole investors who are scared of the dollar value. The value of the U.S. Dollar has jumped significantly this month. This means that investors can now move their money to a different part of the market to make far more than they can with commodities like oil, so they bail and the demand for the stock drops, causing the price of the stock to drop.
Now then, how does adding in an extra tax have any affect on a market that is barely driven by supply and demand? It doesn't. An extra tax will cost everyone money, the market simply doesn't give a shit about correcting for it. JeffMeden's argument only works if it would cause lopsided competitiveness, where one gas station would have to mark up or down to match the station across the street, which simply isn't the case with a tax levied against everyone.
Now, if anyone is still reading, here is something else to chew on. Where would this extra gas tax go? Not to fixing the roads, that doesn't happen regardless of how much cash is in the fund. Nope, it goes into a fund available to the public for certain recreational activities, and groups can apply for these funds. Most of it in Ohio goes to state parks and hippie groups that want horse or walking trails. Now, prove to me that increasing the gas tax is going to anything other than pad a fund that doesn't really get used anyway.