Bangkok's rapid growth coupled with little urban planning has resulted in a haphazard cityscape and inadequate infrastructure. Despite an extensive expressway network, an inadequate road network and substantial private car usage have led to chronic and crippling traffic congestion, which caused severe air pollution in the 1990s. The city has since turned to public transport in an attempt to solve the problem, operating five rapid transit lines and building other public transit, but congestion still remains a prevalent issue. The city faces long-term environmental threats such as sea level rise due to climate change.