Monorail is a subtheme of Service Packs introduced in 1989 and currently consists of 3 sets. All sets were released in 1989. As of today, the average annual growth of sets in Service Packs Monorail is approximately 5.6% per year.
The LEGO Service Packs theme refers to supplementary sets that were released primarily from the late 1970s to the late 1990s. These packs provided additional parts, accessories, or specific components to complement existing LEGO sets. Rather than complete standalone models, Service Packs were intended to enhance or expand upon primary LEGO sets, allowing users to replace missing pieces, add more features to their builds, or customize their creations further.