diff --git a/src/edu/kit/informatik/Main.java b/src/edu/kit/informatik/Main.java
index d2f2098..4e63f0c 100644
--- a/src/edu/kit/informatik/Main.java
+++ b/src/edu/kit/informatik/Main.java
@@ -2,7 +2,17 @@ package edu.kit.informatik;
 
 import edu.kit.informatik.ui.CommandLine;
 
+/**
+ * The main class.
+ * 
+ * @author Arne Keller
+ * @version 1.0
+ */
 public class Main {
+    /**
+     * Program entry point.
+     * @param args command-line arguments
+     */
     public static void main(String[] args) {
         CommandLine.startInteractive();
     }
diff --git a/src/edu/kit/informatik/model/ModelRailwaySimulation.java b/src/edu/kit/informatik/model/ModelRailwaySimulation.java
index 21e5109..29c2995 100644
--- a/src/edu/kit/informatik/model/ModelRailwaySimulation.java
+++ b/src/edu/kit/informatik/model/ModelRailwaySimulation.java
@@ -376,26 +376,23 @@ public class ModelRailwaySimulation {
     public boolean putTrain(final int trainId, final Vector2D position, final Vector2D direction)
             throws InvalidInputException {
         Train train = trains.get(trainId);
-        if (train == null || !train.isProperTrain() || train.isPlaced()) {
-            // can only place valid trains that are not already placed
-            return false;
+        if (train == null) {
+            throw new InvalidInputException("train not found");
+        } else if (!train.isProperTrain()) {
+            throw new InvalidInputException("train is not valid");
+        } else if (train.isPlaced()) {
+            throw new InvalidInputException("train is already placed");
+        } else if (direction.getX() != 0 && direction.getY() != 0) {
+            throw new InvalidInputException("invalid train direction");
         }
-
         // attempt to place train
         boolean placed = train.placeOn(railNetwork, position, direction);
-
-        if (placed) {
-            // now, check for collisions
-            List<HashSet<Train>> collisions = getStaticCollisions();
-            if (!collisions.isEmpty()) {
-                // remove if colliding
-                train.removeFromRails();
-                return false;
-            } else {
-                return true;
-            }
-        } else {
+        // check for collisions
+        if (placed && !getStaticCollisions().isEmpty()) {
+            train.removeFromRails();
             return false;
+        } else {
+            return placed;
         }
     }
 
diff --git a/src/edu/kit/informatik/ui/InvalidInputException.java b/src/edu/kit/informatik/ui/InvalidInputException.java
index 057ac85..ee11fe1 100644
--- a/src/edu/kit/informatik/ui/InvalidInputException.java
+++ b/src/edu/kit/informatik/ui/InvalidInputException.java
@@ -8,7 +8,7 @@ package edu.kit.informatik.ui;
  */
 public class InvalidInputException extends Exception {
     /**
-     * Construct a new invalid input expection.
+     * Construct a new invalid input exception with a specific message.
      * @param message the error message
      */
     public InvalidInputException(final String message) {
diff --git a/src/edu/kit/informatik/ui/command/CommandFactory.java b/src/edu/kit/informatik/ui/command/CommandFactory.java
index fb0ed1f..39bb93f 100644
--- a/src/edu/kit/informatik/ui/command/CommandFactory.java
+++ b/src/edu/kit/informatik/ui/command/CommandFactory.java
@@ -49,7 +49,7 @@ public class CommandFactory {
     private static final String SHOW_TRAIN = "show train";
     private static final String PUT_TRAIN = "put train";
     private static final Pattern PUT_TRAIN_ARGUMENTS
-        = Pattern.compile(" \\+?(\\d+) at \\(([+-]?\\d+,[+-]?\\d+)\\) in direction ([+-]?\\d+),([+-]?\\d+)");
+        = Pattern.compile(" \\+?(\\d+) at \\(([+-]?\\d+,[+-]?\\d+)\\) in direction ([+-]?\\d+,[+-]?\\d+)");
     private static final String STEP = "step";
     private static final String POSITIVE_NUMBER = " \\+?\\d+";
 
@@ -68,11 +68,7 @@ public class CommandFactory {
             }
             Vector2D start = Vector2D.parse(matcher.group(1));
             Vector2D end = Vector2D.parse(matcher.group(2));
-            if (start.getX() == end.getX() || start.getY() == end.getY()) {
-                return new AddTrack(start, end);
-            } else {
-                throw new InvalidInputException("invalid track segment: not a straight line");
-            }
+            return new AddTrack(start, end);
         } else if (command.startsWith(ADD_SWITCH)) {
             String arguments = command.substring(ADD_SWITCH.length());
             Matcher matcher = ADD_SWITCH_ARGUMENTS.matcher(arguments);
@@ -205,12 +201,8 @@ public class CommandFactory {
             }
             int id = Integer.parseInt(matcher.group(1));
             Vector2D point = Vector2D.parse(matcher.group(2));
-            int x = Integer.parseInt(matcher.group(3));
-            int y = Integer.parseInt(matcher.group(4));
-            if (x != 0 && y != 0) {
-                throw new InvalidInputException("invalid train direction");
-            }
-            return new PutTrain(id, point, x, y);
+            Vector2D direction = Vector2D.parse(matcher.group(3));
+            return new PutTrain(id, point, direction);
         } else if (command.startsWith(STEP)) {
             String argument = command.substring(STEP.length());
             if (!argument.matches(" [+-]?\\d+")) {
diff --git a/src/edu/kit/informatik/ui/command/DeleteTrain.java b/src/edu/kit/informatik/ui/command/DeleteTrain.java
index 21150f9..9f04422 100644
--- a/src/edu/kit/informatik/ui/command/DeleteTrain.java
+++ b/src/edu/kit/informatik/ui/command/DeleteTrain.java
@@ -11,7 +11,7 @@ import edu.kit.informatik.Terminal;
  */
 public class DeleteTrain extends Command {
     /**
-     * Identifer of the train to delete.
+     * Identifier of the train to delete.
      */
     private final int id;
 
diff --git a/src/edu/kit/informatik/ui/command/PutTrain.java b/src/edu/kit/informatik/ui/command/PutTrain.java
index 085d455..8a26b79 100644
--- a/src/edu/kit/informatik/ui/command/PutTrain.java
+++ b/src/edu/kit/informatik/ui/command/PutTrain.java
@@ -12,28 +12,34 @@ import edu.kit.informatik.ui.InvalidInputException;
  * @version 1.0
  */
 public class PutTrain extends Command {
+    /**
+     * Identifier of the train to place.
+     */
     private final int id;
+    /**
+     * Where to place the train.
+     */
     private final Vector2D point;
-    private final int x;
-    private final int y;
+    /**
+     * Initial direction of the train.
+     */
+    private final Vector2D direction;
 
     /**
      * Construct a new 'put train' command.
      * @param id identifier of the train
      * @param point where to put the train
-     * @param x initial x direction
-     * @param y initial y direction
+     * @param direction initial direction
      */
-    public PutTrain(final int id, final Vector2D point, final int x, final int y) {
+    public PutTrain(final int id, final Vector2D point, final Vector2D direction) {
         this.id = id;
         this.point = point;
-        this.x = x;
-        this.y = y;
+        this.direction = direction;
     }
 
     @Override
     public void apply(final ModelRailwaySimulation simulation) throws InvalidInputException {
-        if (simulation.putTrain(id, point, new Vector2D(x, y))) {
+        if (simulation.putTrain(id, point, direction)) {
             Terminal.printLine("OK");
         } else {
             Terminal.printError("could not place train");
diff --git a/src/edu/kit/informatik/ui/command/SetSwitch.java b/src/edu/kit/informatik/ui/command/SetSwitch.java
index d0126d1..e3a78bf 100644
--- a/src/edu/kit/informatik/ui/command/SetSwitch.java
+++ b/src/edu/kit/informatik/ui/command/SetSwitch.java
@@ -11,7 +11,13 @@ import edu.kit.informatik.Terminal;
  * @version 1.0
  */
 public class SetSwitch extends Command {
+    /**
+     * Identifier of the switch to configure.
+     */
     private final int id;
+    /**
+     * Position to set the switch to.
+     */
     private final Vector2D point;
 
     /**
@@ -21,7 +27,8 @@ public class SetSwitch extends Command {
      */
     public SetSwitch(final int id, final Vector2D point) {
         this.id = id;
-        this.point = point;
+        // make sure caller can not modify internal state
+        this.point = new Vector2D(point);
     }
 
     @Override