We appreciate the tips, but this correction calls for some annotation.
What constitutes "downtown" varies with the beholder, but the first lot mentioned is outside the boundaries of the Central Business Improvement District. (We assume the writer is indicating the lot along Patton Street, east of the Old City, and that in offering directions he means Willow or East Jackson, not Locust. The highway above is actually the James White Parkway.) It's within a healthy person's walking distance of downtown, but when we visited it recently, it was furnished with a thin carpet of broken glass, and the only other humans visible were some devil-may-care teenage boys.
The West Jackson lot, between the McClung Warehouse fire site and the underside of the Gay Street viaduct, is certainly downtown. It was recently private property, a prospective construction site. There's no signage today, but it's paved and striped, an apparently free parking lot.
But absence of signage may unsettle the prudent parker. We recall an unmarked lot near Henley which hosted popular free parking for years, only to be visited by a fleet of tow trucks sent by a property owner who, it turns out, was angry at our presumptions all along. The lot under the parkway does include some advice: "Watch for Drainage Above" and "Park at Own Risk." Not that we wouldn't park there.
As for the private surface lot at Central and Summit Hill, in the Old City, it's $3 only until 4, when the rate doubles to $6. Reporters work late. Whether day parkers get an unlimited free ride into the evening isn't clear in the signage, perhaps leaving the matter open to interpretation. When we checked our facts on Monday, a tow truck was dutifully pulling a car left by someone who assumed he could get away with it.