According to the Washington Post, on his radio show on WTOP today the governor said the inside-the-Beltway plan is being changed in response to public comment such that the HO/T operation would apply only in the traditional peak direction (to DC AM, from DC PM).
https://www.washingtonpost.com/local/virginia-politics/mcauliffe-calls-republican-senate-candidate-liar-over-i-66-toll-proposal/2015/10/28/6f819f42-7d91-11e5-beba-927fd8634498_story.html
I find the idea of a mileage tax insidious because it'd be used to open the door to other things. It wouldn't stop at simply recording distance driven. It'd be expanded to track your whereabouts at any given time and to assess whether you're somewhere you "should" be. Doesn't matter what laws might be put in place. The government's secret little stooge court would be used to let them do whatever they want in secret.
Hoo, I have a bigger problem with such taxes, and it relates directly the antics of places like Hopewell, Va. and Takoma Park, Md. and more than a few other municipalities.
Unless mileage-based user fees (MBUF) are set only at the statewide level, small municipalities like those two (and many others) will rationalize the "fairness" of collecting extremely high per-mile fees on traffic only passing through.
On a larger scale, am quite sure that New York City would enumerate the huge expense associated with running its subway and public transit bus systems (and delivering an assortment of other services - mostly to city residents) as excuses to hammer drivers passing though either way on I-95, or trying to get from New Jersey or Westchester County to Nassau County and Suffolk County on Long Island.
That's an interesting point that didn't occur to me when I was typing that post during lunch. Crossing state lines of course means a mileage-based system requires tracking the vehicle's location at all times. Obviously it's not appropriate for the state where the vehicle is registered just to collect a tax on the total distance driven if portions of that were incurred in other states (I guess Hawaii wouldn't face the issue very much). That in turn raises the problem of double taxation if your home state taxes you on the total distance driven and another state makes you pay tax for your distance driven there. This problem already occurs with income tax. Some states won't give you a 100% credit for income tax paid to another state if the other state imposes a higher tax rate than your home state does (I experienced this several times at a prior job where I had to pay New York income tax as a non-resident—Virginia didn't give a 100% credit). I wouldn't be surprised to see something similar happen.
I have not taken the time to think about whether there would be constitutional issues if the US government tried to regulate this sort of thing, and since I'm typing this during intermission of the hockey game I won't be thinking about that tonight. I don't know whether a tax on distance driven would be a "direct tax." Recall the first attempt at a federal income tax was struck down by the Supreme Court and a constitutional amendment was required to allow the current income tax to be collected.
Typing that made me think of the interesting question of whether differing tax rates from state to state could lead to the peculiar situation of people taking longer routes through states with lower rates if doing so could save money. Obviously only a sensible idea up to a certain point, of course.
Regarding the E-ZPass issue, there is a guy on Dr. Gridlock's blog with username "sneedel" who claims his E-ZPass Flex was charged a toll when he was using it in HOV mode. I haven't heard about that from anyone else, and I'm sure the media would have been all over it.
I remember before the Beltway lanes opened some people were convinced the toll gantries would charge people driving in the far left general-purpose lane. I haven't heard of that happening either.