In short about hybrid taxicab in Wikipedia
Hybrid taxi or hybrid electric taxi is a taxicab service provided with a hybrid electric car (HEV), which combines a conventional internal combustion engine propulsion system with an electric propulsion system.
In 2000, North America's first hybrid taxi was put into service in Vancouver, British Columbia, operating a 2001 Toyota Prius which traveled over 332,000 kilometres (206,000 mi) before being retired. Several major cities in the world are adding hybrid taxis to their taxicab fleets, led by San Francisco where hybrid represent almost 50% of its taxicab fleet by March 2010, and New York City where hybrids taxis represent 45% of the city's total fleet by September 2012. Unlike conventional gasoline cars, hybrids get better fuel economy, do well at slow speeds or idling, and have cleaner emissions.
Hackney carriage - Wikipedia
The Beardmore was an alternative taxi design used in London during the 1960s and 1970s
Until the late 1950s, vehicles licensed as London taxis were required to be provided with an open-access luggage platform in place of the front passenger seat found on other passenger cars (including taxis licensed for use in other British cities).
A hackney or hackney carriage (also called a cab, black cab, hack or London taxi) is a carriage or automobile for hire. A hackney of a more expensive or high class was called a remise.
Minimum vehicle class for taxi
Taxis are often middle-class vehicles, usually having air-conditioning, leather seats and other amenities. Most often evokes car brand associated with the taxi is a Mercedes, because it is regarded as the most reliable car manufacturer.
A taxi must be comfortable - so middle class or high. I can not imagine that a taxi could be a car hatchback or van. The air conditioning is absolutely essential, especially on hot days, which is recently more and more. As for the leather seats they are easy to clean and disinfect, and the cleanliness of the taxi is as important as comfort.