UIC 2019 PAS 614 mixed traffic study - Mixed traffic high speed lines operations Handbook

Although currently high-speed railways are almost exclusively associated with passenger services, there is a current trend to increase the efficiency of high-speed lines incorporating certain rail freight services, in some cases with daytime integration of freight trains, and in others only with night time traffic. 

The new sections of the European corridors, which are forecasted to complete the Core Network, expect all types of traffic with the scope of maximizing their incomes, such as those that would come from their shared use with the lines for passenger transportation at 250 km/h, goods transportation, and even, in some specific sections, with regional intercity trains operating in services over 200 km, which are considered for high speed. 

In addition, these new mixed traffic lines can directly contribute to the decongestion of network sections, bottlenecks where there are saturation problems and therefore there is an under-development of rail transport.