We love high speed trains. But LEGO trains have limitations - power and track geometry.
French AFOLs, during events such FanaBriques, make use of modified tracks (seamless) and professional power supply (up to 30V with no amperage limitations) to set up a very high speed track on which people race with their "9V" high speed train creations.
But that's a lot of work and Daniel Stoeffler has a simplier solution for you to setup a powered high speed track.
To summarize, to get about 18V of voltage in the track (twice the regular value) , he uses two speed regulators.
LEGO train fans are used to plug multiple speed regulator units on a single layout, but always as parallel circuit. This way, they manage to power multiple train motors without seeing electric current collapses.
But you still obtain only 9V into the rail.
To get 18V, Daniel add an extra piece of track, pluging the + of one speed regulator to the - of the other one (a serie circuit) as shown here.
It's so simple that I'm surprised it has not been done before.(?)
Concerning the track geometry, Daniel uses a modified HLC (Holger Large Curve) well known to RailBricks magazine readers.
So far, Daniel's train motors and speed regulators had not been damaged but you operate such a build at your own risk.