Thunderbirds (1965)

S1E22 Brink of Disaster

A deceitful investor seeks to persuade Lady Penelope to back his ambitious automated monorail project spanning the country. Eager to help, Jeff offers to test the prototype, but he, Brains, and Tin-Tin soon face a dire situation when they realize they are trapped inside the train. Their predicament worsens as they hurtle toward a damaged bridge with no means of stopping in sight.