While driving a train in manual mode, use CTRL+Q hotkey in order to enable maneuver directions. When approaching a rail junction, you will see the labels indicating which direction is left, which is right and which is straight ahead. Simple.

Changelog

• 0.0.4 - release for Factorio 0.15
• 0.0.3 - fixed a bug which caused a game error when entering a car/tank
• 0.0.2 - improved detection of junctions
• 0.0.1 - initial version