&gt; But we actually may use a G-seats.<p>For what purpose? A souped up train isn&#x27;t going to do high-g manoeuvres.<p>&gt; It may break your neck on sudden deceleration though.<p>The only deceleration for which that&#x27;d happen is an explosive one where you&#x27;d dismantle the carriage into a wall (and even then it&#x27;s unlikely to break your neck), and a broken neck would be the least of your worries.