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Sound Transit 2 Greenhouse Gas Emissions

Sound Transit proposed an expansion plan called Sound Transit 2 (ST2) that would extend the existing light rail system to serve three major travel corridors. The plan will add 36 miles of light rail and streetcar line to the initial 13.9 miles between downtown Seattle and Sea-Tac Airport. Link light rail would extend from North Seattle into Snohomish County; across Lake Washington into East King County; and south of Sea-Tac International Airport to Federal Way. ST2 would also significantly expand Sounder commuter rail and ST Express regional bus service.


As part of the overall planning effort, WSP USA conducted a sustainability assessment of the ST2 light rail expansion plan that estimated how the operation of the system would affect greenhouse gas (GHG) emissions in the region. Included in the sustainability assessment were GHG emissions reported in terms of carbon dioxide equivalents resulting from estimated changes in electric power demands needed to operate the Sound Transit system, and forecasted changes in vehicle miles traveled for general roadway traffic and other transportation modes. The analysis used area-specific power generation emission factors as well as incorporated projected vehicle fuel efficiencies.

We also conducted an energy security assessment to evaluate how the electric light rail expansion would increase the diversification of energy sources used for transportation in the region, which may be important if the cost of petroleum-based or other liquid fuels continues to increase and/or in the event of liquid fuel supply disruptions. In November 2008, voters in the Puget Sound region approved this plan for extending light rail in the region.