The electric grid is more and more under pressure. A blackout is possible. In Europe and particularly in France, during cold period the consumption reaches a share of production capacity higher and higher every year. Moreover, the increasing part of intermittent energy sources coupled with a drop of peak production sources investments are nowadays impacting the electric grid stability. With electricity market liberalization and new mechanisms, not only producers can be a part of electricity grid stability, consumers can. The most consuming industries can act and participate in these mechanisms (demand-response). In France the first consumer is the main French railway operator SNCF. Its presence all over France makes it relevant as a distributed-but-unique service provider. In a societal point of view, SNCF, as a public industry, is legitimate to make efforts towards electric grid stability avoiding home or region blackout due to unbalance between consumption and production. SNCF yearly power consumption of 8 TWh is exposed in this paper, showing a distribution of 84% for traction, 14% for buildings and stations, and 2 % for rolling stock maintenance centres. Rolling stock involvement in demand-response mechanism is meaningful. But reducing the power of a train may involve a delay at arrival that is not acceptable for passengers. Many Driver Advisory Systems (DAS) on the market owe to reduce energy consumption. The objective of this paper is to show the development of a new add-on in a DAS that will optimize power reduction of trains during a balancing period and ensure the arrival time, while controlling the energy consumed during the overall trip. A demand-response period is added in the optimisation tool to get involved in electricity market mechanisms. A virtual test is done on high speed line “LN1” between Paris and Lyon. Different scenarios are presented and show a flexibility potential between 3 to 7 MW during peak hour involving 15 High Speed Trains (HST). The economic potential of this implication is finally detailed. On a national basis, it represents a big share of electrical primary reserve and is also a matter of concern for network operators and utilities.