Problems on Trains
Problems on Trains
Train problems apply TSD with one twist: a train has length, so the crossing distance equals train length plus obstacle length. SSC CGL Tier 1 and RRB exams carry 2\u20134 train questions per paper across three types: pole, platform, and two-train crossings. Convert km/h to m/s (\u00D75/18) before plugging into any formula \u2014 unit mismatch is the most common error.
Key Idea
Distance = length of train + length of obstacle. Opposite directions: add speeds. Same direction: subtract speeds. Always match units — km/h to m/s using ×5/18.
Core Formulas
Cross pole/person
Time = Length of train / Speed of train
Use when a train passes a pole, signal post, or standing person \u2014 the object has zero length, so distance equals the train\u2019s own length.
Cross platform
Time = (L_train + L_platform) / Speed
Add the platform (or bridge) length to the train\u2019s length to get total crossing distance, then divide by speed.
Opposite direction
Time to cross = (L₁ + L₂) / (S₁ + S₂)
Two trains coming towards each other
Same direction
Time to cross = (L₁ + L₂) / (S₁ − S₂)
Faster train overtaking slower train
Speed conversion
1 km/h = 5/18 m/s; 1 m/s = 18/5 km/h
Essential unit conversion for train problems
Relevant Exams
2–4 questions per exam in SSC CGL Tier 1 and RRB exams. Train problems are among the most frequently asked TSD applications. Three types: pole, platform, two trains.