Kraftwerk's fourth album defined their style and put them on the musical map. While their earlier records had been full of spacy atmospheres but relatively little synthesizer, Autobahn is where they began to incorporate conventional, somewhat pop-oriented song structures and rhythms. The tracks are still mostly instrumental, but the infectious little vocal refrain on the 22-minute title track helped make the three-minute excerpt issued as a single an international hit. While much of the album still features cosmic-sounding textures, the organ riff that emerges toward the end of "Kometenmelodie 2" could have come from a bubblegum pop tune. And the piano, flute, and acoustic guitar at the end of the closing cut, "Morgenspaziergang," can be seen as a farewell to the non-electronic side of the band's early sound.