Utility tricycles got widespread in the 3rd-world kinda recently, even though more focused in the light commercial vehicles market, surpassing the social stigma regarding them as somewhat "inferior" to a conventional 4-wheel automobile. The space they take on the streets, compared to a small car of comparable role, makes them an attractive option for door-to-door parcel delivery and other tasks requiring an enhanced maneuverability in tight corners and ease of parking. But would these vehicles still be viable in developed countries?
There are some challenges that can make a tricycle less attractive in
developed markets. From a 3rd-world perspective, the lack of a good
all-weather protection is often excused due to the cost it would add,
while a lower running cost is the main priority over the comfort.
However, it's not impossible to find some models equipped with a
fully-enclosed cabin, also featuring car-like controls instead of a
motorcycle-type handlebar, and seating capacity for at least one
passenger. Switching the engine from a rather outdated air-cooling
layout to liquid-cooling also makes it easier to provide heating. With all the improvements that can be applied to a tricycle, it turns them into an attractive option over a regular coupé-utility such as the Fiat Strada, which had been available in selected European markets in spite of catering to the 3rd-world.
Utility tricycles such as the Innocenti Lambro and the Piaggio Ape (ah-pay, "bee" in Italian) actually had their days of glory in Western Europe and, due to their suitability to many purposes from light cargo hauling to passenger transportation, their key role in the rebuilding of Italy and other countries devastated by the horrors of World War II is not to be forgotten. Agile, cheap to operate, and more affordable than a comparable 4-wheeled vehicle of the austerity days in the immediate post-war period, they were a perfect option to roam around the narrow streets and alleys of the European cities. The lower fuel consumption and fewer tyres were also very desirable due to the scarcity of resources at that time.
An Indian derivative of the Piaggio Ape, the Bajaj RE, available with 2-stroke (RE2S) and 4-stroke (RE4S) gasoline-powered engines also available in gaseous-fuel versions using either CNG or LPG, and Diesel options, became very popular for passenger transportation as an alternative to conventional taxis that are more expensive. Their enhanced maneuvering in tight spaces also helps to deal with the overcrowded urban traffic, while the low top speed is not so much of a problem in precarious Indian roads and the 3-wheel layout actually reduces the frame stress dealing with irregular pavements. Even though the aptitude to go through unimproved terrain is virtually negligible by modern European standards, and the modest performance would be deemed undesirable by potential customers looking for an all-around vehicle, the basic concept of a tricycle still provides some room for improvements.
But would a tricycle be still competitive in a market where cars as small as the Smart ForTwo and fuel-sippers like the Toyota Prius are available? Probably. The lesser amount of raw materials required in the manufacturing of a tricycle and the replacement parts needed throughout its useful life is favorable to them from a "sustainability" standpoint so much as the low fuel consumption is. And even though it's not technically impossible to apply a hybrid drivetrain into a tricycle, it's not really essential in order to achieve outstanding fuel-efficiency values and cut tailpipe emissions.
No matter if they're based around a 125cc motorcycle or specifically-developed as a tricycle like the Can-Am Spyder, these vehicles usually still hold the legal status of a motorcycle, thus retaining a more compact size and lower weight as they don't have to comply to modern crash-worthiness standards that are often blamed for the size, weight and complexity increase in newer cars. Some customers may still prefer the allegged safety advantage of a car but, as I never saw anybody buying one willing to hit it into a concrete wall, a tricycle still sounds reasonable.