Road Trip. The New Yorker, Jan. 18, 2021.
Below are directions for the first of David Hockney's Wagner Drives, the Malibu Canyon version. The Adrian Boult recordings that Hockney used are not easily available, but substitutes with similar timings are suggested below.
1. Begin at the corner of Las Flores Canyon Road and Pacific Coast Highway. Play "America" from West Side Story. Repeat if necessary until step 2.
2. Turn right onto Malibu Canyon Road. Play "The Entrance of the Gods into Valhalla" from Das Rheingold, duration 8:49. Suggested recording: Gustavo Dudamel conducting the Simón Bolivar Symphony Orchestra (DG).
3. Turn right onto Piuma Road; after 6.4 miles, continue briefly onto Rambla Pacifico. Play the Prelude to Act I of Parsifal, duration 12:45. Suggested recording: Georg Solti conducting the Vienna Philharmonic (Decca).
4. Turn left onto Las Flores Canyon Road and return to the PCH. Siegfried's Funeral Music from Götterdämmerung, duration 8:14, should be beginning at about this time. Suggested recording: Gustavo Dudamel / Simón Bolivar (DG).
The Kanan Dume drive is more difficult to replicate, but I've traced the route on Google Maps. The playlist is: "America," "Blue Danube" Waltz, Entrance of the Gods (at the turn onto Kanan Dume), Parsifal Act I Prelude, Parsifal Act I Transformation music, Parsifal Good Friday music, Siegfried's Funeral Music, Parsifal Act I Prelude.
Directions for the San Gabriel drive are here. The playlist is: three Sousa marches (Hands Across the Sea, The Thunderer, The Belle of Chicago), Entrance of the Gods, first movement of Schumann's "Rhenish" Symphony, Parsifal Act I Prelude, second movement of the "Rhenish," Sousa's Liberty Bell march.
Much thanks to Arthur Kolat for making these expeditions possible. His excellent thesis Twilight of the Roads can be found at Academia.edu.