I have several times in the past used the Metro at Vienna. It's the one furthest west, and the one that you need to take if you want to avoid the I-66 eastbound parking lot on a rainy morning. I have
discussed before how mystifying it is to me that no one builds more parking, and charges for it.
Well....I got there Tuesday, at 9:15 am. Didn't find a space, drove around. Very nearly got hit, twice, by different people who were doing about 45 mph in the parking garage and making left turns without looking if someone was coming straight. One of them blew her horn at ME! (I made no gesture, or sound, other than a look of mild surprise, which I thought was an understated reaction, by the standards of the Angus / Mungowitz apoplexy-for-small-slights scale).
Parking appeared to be totally free. No parking attendants, the bars at the entrance and exit booths were raised. So, every space was full, in every lot and every garage.
Now, this makes no sense. Consider:
1. We subsidize the Metro already....a LOT. The argument for why parking should be subsidized is that "we" (really? no one asked me) "we" want people to use the Metro. (Me? I want them to walk...through the woods....and chiggers on their tingly parts)
2. Since it's free, people use it....too much. Charge something.
3. At a minimum, have some spaces, extra spaces, where you charge something. A LOT, if necessary, to make sure that there are SOME spaces available, for a high price. Who would be deterred by high prices? Those who could most easily find a ride, or take a bus. Who would use high-price parking spaces? Those who have the highest value of time, or the most urgent errand. Who would benefit? Well, imagine sorting people by their need to park. The last person who parked free on that day is likely nearly indifferent between parking and taking a bus. Having that person take the bus is a tiny cost. The next person who could have parked, at (say) $2/hour must really need to park, and ride. And the revenues of the system would go up, and the required subsidy (see above) would go down.
4. To be fair, there IS an alternative. you can park at the meters, outside. And, there were several meters available. Dozens, in fact. All you need is (I'm not making this up) $1 coins. Do you happen to have several of those? Like, six or eight, in your pocket? I sometimes get a $1 coin, and have 1 1$ coin, until I can foist it off on the next loser I buy something from. Now, lots of places (LOTS of places; that's a parking joke) have those stands where you put in your credit card, and pay, and get a receipt, and put it on your windshield. Even if you had to walk
50 yards to one of the machines, at least it is POSSIBLE to park there. The nominal price of these meters, as it stands, is $1 per hour. The actual price is effectively infinity, since NOBODY CARRIES F*****G 1$ coins.
So, I walked to the Metro station, bought my ticket with a $10, got 5 1$ coins in change from the machine, walked back to my spot, and put $5 worth of coins in the machine. I got back 5 hours and 45 minutes later, and there was a parking ticket disintegrating in the rain on my windshield. (There had been a 40 minute delay while something was cleared off the track, but I might have been late anyway. I hope they were clearing the remains of the guy who decided parking at Vienna should be free, and that he got hit while explaining some commuter why we need more subsidies, so parking can be free, so we get more riders, so we need more subsidies).

Two solutions, one from me, one from my lovely wife.
1. (mine) Lose the meters, which are electric and expensive. Install those machines that take credit cards. Charge $10/day, fixed rate, or $1.50 /hour.
2. (hers) there is plenty of free parking available, right out on I-66. You can leave your car there from 7:30 am til at least 10 am, and no one would notice, because there is no traffic movement. Sure, after 10 am you might get towed. But think how CONVENIENT it is.