In DC every bike lane that is painted is a bike lane, no different than any other, but in Arlington that's not necessarily true.
In DC a bike lane is defined by DC Regulations (DCMR 24-3399)
a portion of a roadway that has been designated for preferential or exclusive use by bicyclists by pavement markings and, if used, signs.
And that is similar to the definition in Virginia
"Bicycle lane" means that portion of a roadway designated by signs and/or pavement markings for the preferential use of bicycles, electric power-assisted bicycles, and mopeds.
But in Arlington the county code states that (bolded by me)
Where the County Board has by ordinance designated a bicycle lane for the exclusive use of bicycles, a motor vehicle may cross a bicycle lane for the purpose of entering or exiting adjacent property, for making a turn, or for the purpose of parking, but no person shall stop, stand or park a motor vehicle in a bicycle lane, nor shall any person drive a motor vehicle in a bicycle lane for a distance of more than one hundred (100) feet.
And there is some concern that this preempts state code. It certainly confuses it. The main difference here is that in DC and by Virginia code it is the markings on the street or signage that makes it a bicycle lane - with all the restrictions that that entails, while in Arlington it may be a bike lane, but motor vehicles are not restricted if the County Board had not designated it a bicycle lane by ordinance.
Some bike lanes in the County have been designated, and some have not.
It might seem like a trivial footnote or loop hole, but the recent ruling in Montgomery County on cyclists in crosswalks brings to light how important it is to clarify the law.