A small vehicle with engines on wheels that are separate from the carriage itself, pulling it forward. They are also known as "Paddy Wagons" or more generally "coaches".
Steambikes are a technological cousin.
They are an extremely common mode of transportation. Typical configurations are two or four engines. Single engine carriages are rare.
They may have a heavily armored compartments with gun emplacements and cannon attachments. These particular carriages are used by police and militia.