The collapse of a billboard along the Brooklyn-Queens Expressway on Jan. 13 has turned the city’s attention again to the presence of highway billboards: how many are legal, how many are safe and what are they doing there in the first place? “In the realm of outdoor advertising in the city, definitive answers can be elusive,” Patrick McGeehan reported in The Times on Friday.

What is beyond doubt is how much of an impact billboards have on the cityscape.

City Room took a walk along the stretch of the Long Island Expressway viaduct outside the Queens-Midtown Tunnel where there is a high concentration of enormous “bulletin” billboards, many of which sprout from the pavement like steel sequoias.

Although many billboards achieve quasi-legality through a loophole that protects advertising for the businesses in the buildings to which the signs are attached, few of them in that area have anything to do with local businesses, unless the new cable series “Spartacus: Vengeance” is secretly being filmed on location in Hunters Point, or the little parking lot office at Borden Avenue and Vernon Boulevard has suddenly become a Lacoste outlet.

It may be hard to argue that the billboards terribly disfigure an otherwise unlovely industrial environment. But it’s easy to see that they take up a lot of sky.