Many governments in different parts of the world are investing in high speed rail. Some of them do so thinking that it will be an important part of climate change mitigation. Intercity traffic over medium distances is particularly interesting in the environmental context as it constitutes the only transport segment where aircraft, trains, coaches and cars naturally compete for market shares. This report calculates the effect on emissions from building a new high speed link that connects two major cities located 500 km apart. It assumes that emissions from new vehicles and aircraft in 2025 can be used as a proxy for the emissions during a 50 year investment depreciation period. The emissions from the marginal production of electricity, used by rail and electric vehicles, are estimated to amount on average to 530 gram per kWh for the entire period. Fuels used by road vehicles are assumed to be on average 80 percent fossil and 20 per cent renewable (with a 65% carbon efficiency in the latter case).