Plans to convert traffic-congested key shopping hubs into pedestrian precincts are expected to be announced by the Hong Kong Government today. The announcement, which will coincide with World Environment Day, will signal the Planning, Environment and Lands Bureau's intention to improve air quality in Causeway Bay, Yau Ma Tei, Tsim Sha Tsui and Mongkok, which are plagued by high pollution levels. The plans will be added to the Hong Kong Island North and Kowloon West District Traffic Study conducted by Ove Arup and Partners, commissioned by the Transport Department last October. Under the proposals, only smoke-free vehicles, such as trams and electric minivans, will be allowed access to a large area of Causeway Bay.