In 1958, there were more than 4,000 drive-in theaters in the U.S. Today, only 368 remain, according to figures complied by the United Drive-in Theater Owners Assn. Some of the facilities are the outdoor versions of multiplexes, so the total number of drive-in screens is 661.Pennsylvania has the most sites, with 33 drive-ins and 54 screens. Four states (Alaska, Delaware, Hawaii and Louisiana) and Washington, D.C., have none. Unlike other 1950s staples such as bobby socks and Brylcreem, drive-in theaters have staged a modest comeback over the past couple of decades. According to the theater owners’ data, 42 drive-ins have been built since 1990, and only four of them have since closed. Over the same period, 63 drive-ins were re-opened, and just 11 of them have since been shuttered. Alabama had the most new builds at nine (one since closed), while Texas counted the most new builds plus re-openings at 15, with three now closed. Nobody publishes figures on drive-in grosses, but it’s possible to guess at the number by extrapolating from total domestic box office grosses, which boxoffice.com measured as $10.19 billion in 2011. Assuming every U.S. screen delivered the same results, drive-ins would have grossed a little shy of $170 million last year. Of course, that probably overstates the drive-in business. Unlike their hard-top brethren, drive-in owners can’t add earlier showings to capitalize on boffo hits. But a few are investing in digital projection, and one Texas drive-in now offers 3D screenings.