diff --git a/src/edu/kit/informatik/model/TrainManager.java b/src/edu/kit/informatik/model/TrainManager.java
index 73aa75c..9417140 100644
--- a/src/edu/kit/informatik/model/TrainManager.java
+++ b/src/edu/kit/informatik/model/TrainManager.java
@@ -146,12 +146,13 @@ public final class TrainManager {
     }
 
     /**
-     * Place a train on the rail network.
+     * Attempt to place a train on the rail network.
+     *
      * @param trainId identifier of the train to place
      * @param position where to place the train
      * @param direction direction in which the train should initially go
      * @return whether the train was successfully placed
-     * @throws InvalidInputException when the train is too long
+     * @throws InvalidInputException if train could not be placed due to semantic error
      */
     public boolean putTrain(int trainId, Vector2D position, Vector2D direction) throws InvalidInputException {
         final Train train = trains.get(trainId);
@@ -168,7 +169,7 @@ public final class TrainManager {
         }
         // attempt to place train
         final boolean placed = train.placeOn(railNetwork, position, direction);
-        // check for collisions
+        // check for collisions with existing trains
         if (placed && !getPlacementCollisions().isEmpty()) {
             train.removeFromRails();
             return false;
@@ -178,7 +179,7 @@ public final class TrainManager {
     }
 
     /**
-     * Calculate the next train identifier.
+     * Calculate the next available train identifier.
      * @return the next train identifier, or -1 if none available
      */
     private int getNextTrainIdentifier() {
@@ -222,7 +223,7 @@ public final class TrainManager {
     private List<Set<Train>> getPlacementCollisions() {
         final List<Set<Train>> collisions = new ArrayList<>();
         trains.values().stream().filter(Train::isPlaced).forEach(train1 ->
-                trains.values().stream().filter(train -> train != train1).filter(Train::isPlaced).forEach(train2 -> {
+                trains.values().stream().filter(Train::isPlaced).forEach(train2 -> {
                     final Set<Rail> occupiedByTrain1 = train1.getOccupiedRails();
                     Collections.addAll(occupiedByTrain1, railNetwork.findTouchingRails(train1.getFrontPosition()));
                     Collections.addAll(occupiedByTrain1, railNetwork.findTouchingRails(train1.getRearPosition()));