Taking a dab pen (THC vape) on a train involves significant legal risk, particularly on interstate services like Amtrak in the United States. Even if you are traveling between two states where cannabis is legal, Amtrak operates under federal jurisdiction, where marijuana and its derivatives remain illegal "Schedule I" substances. While train security is generally less intensive than airport TSA, Amtrak Police and drug-detection K9 units do patrol major stations and trains. In Europe and the UK, the risks are even higher; the UK treats THC as a Class B drug, and crossing international borders (e.g., via Eurostar) involves strict Customs checks where possession can lead to immediate arrest, heavy fines, and a travel ban. For local commuter trains within a legal state, the risk is lower, but using the device on board is strictly prohibited and can lead to detrainment and fines. It is always safest to assume that "federal territory" rules apply the moment you step onto a major rail platform.