Maybe Dragnet was an early manifestation of product placement. Buick might have paid the producers to use Buicks instead of Fords as police cruisers.
In,1955, the California Highway Patrol actually did use Buick Centurys for patrol cars. These Buicks were two door models not available to the public (the two door hard top was available to the public, but not the two door post sedan). These Buicks had the 3 speed column shift manual transmissions. The TV Highway Patrol was realistic it’s first season in using this model Buick. The later years of the show, Buicks, Oldsmobiles, Mercury’s and Dodges were used.