Motorbikes are the primary form of transportation in Vietnam.

In numerous cultures, motorcycles are the primary means of motorised transport. According to the Taiwanese government, for example, "the number of automobiles per ten thousand population is around 2,500, and the number of motorcycles is about 5,000."In places such as Vietnam, motorised traffic consist of mostly motorbikes due to a lack of public transport and low income levels that put automobiles out of reach for many.
The four largest motorcycle markets in the world are all in Asia: China, India, Indonesia, and Vietnam. The motorcycle is also popular in Brazil's frontier towns. Amid the global economic downturn of 2008, the motorcycle market grew by 6.5%.
Recent years have seen an increase in the popularity of motorcycles elsewhere. In the USA, registrations increased by 51% between 2000 and 2005. This is mainly attributed to increasing fuel prices and urban congestion, but is also partly due to television programmes such as reality show American Chopper, or adventure-travel shows such as Long Way Down.

source:http://en.wikipedia.org/wiki/Motorcycle