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midibus

n. A single-decker bus, generally smaller than a traditional bus but larger than a minibus.

Wikipedia
Midibus

A midibus is a classification of single-decker minibuses which are generally larger than a traditional minibus but smaller than a full-size single decker and can be anywhere between and long. While used in many parts of the world, the midibus is perhaps most common in the United Kingdom, where operators have found them more economical, and to have a sufficient number of seats compared to full size single-decker buses.

Midibuses are often designed to be lightweight to save on diesel fuel (e.g. smaller wheels than on larger buses), making them not as durable as heavier 'full size' buses. Some midibuses, such as the Scania OmniTown, are heavier and therefore more durable. In some places such as Hong Kong, some bus routes have to be served by midibuses due to the winding roads along such routes.