Earth excavation was conducted between walls once they were installed, and box structures were built using a bottom-up construction method. Temporary decking constituted the top of the boxes, and the decking both braced the excavation and supported the walls and Second Avenue traffic. The stations at 86th and 72nd Streets were mined.
Fine particulates (PM 2.5) and sulfate aerosols, which may be released in traffic exhaust fumes, are associated with a slightly increased risk. For nitrogen dioxide, an incremental increase of 10 parts per billion increases the risk of lung cancer by 14%. Outdoor air pollution is estimated to cause 1–2% of lung cancers.
Areas where the earth has been disturbed (e.g. construction sites, subdivisions, and transportation corridors) may create acid rock drainage. In many localities, the liquid that drains from coal stocks, coal handling facilities, coal washeries, and coal waste tips can be highly acidic, and in such cases it is treated as acid mine drainage (AMD).
Historically many roads were simply recognizable routes without any formal construction or some maintenance. The Organization for Economic Co-operation and Development (OECD) defines a road as "a line of communication (travelled way) using a stabilized base other than rails or air strips open to public traffic, primarily for the use of road motor vehicles running on their own wheels", which ...