Bangkok's rapid growth in the 1980s resulted in sharp increases in vehicle ownership and traffic demand, which have since continued—in 2006 there were 3,943,211 in-use vehicles in Bangkok, of which 37.6 percent were private cars and 32.9 percent were motorcycles. These increases, in the face of limited carrying capacity, caused severe traffic congestion evident by the early 1990s. The extent of the problem is such that the Thai Traffic Police has a unit of officers trained in basic midwifery in order to assist deliveries which do not reach hospital in time. While Bangkok's limited road surface area (8 percent, compared to 20–30 percent in most Western cities) is often cited as a major cause of its traffic jams, other factors, including high vehicle ownership rate relative to income level, inadequate public transport systems, and lack of transportation demand management, also play a role. Efforts to alleviate the problem have included the construction of intersection bypasses and an extensive system of elevated highways, as well as the creation of several new rapid transit systems. The city's overall traffic conditions, however, remain poor.