diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/Coach.java b/src/edu/kit/informatik/modelrailwaysimulator/model/Coach.java
index 7b37ce9..ae91358 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/Coach.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/Coach.java
@@ -1,7 +1,5 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
-
 import java.util.regex.Pattern;
 
 import static edu.kit.informatik.modelrailwaysimulator.ui.command.CommandFactory.NUMBER;
@@ -34,12 +32,12 @@ public abstract class Coach extends RollingStock {
      * @param length length of coach
      * @param couplingFront whether the coach should have a front coupling
      * @param couplingBack whether the coach should have a back coupling
-     * @throws InvalidInputException on invalid user input (e.g. zero-sized coach)
+     * @throws LogicException on invalid user input (e.g. zero-sized coach)
      */
-    public Coach(int identifier, int length, boolean couplingFront, boolean couplingBack) throws InvalidInputException {
+    public Coach(int identifier, int length, boolean couplingFront, boolean couplingBack) throws LogicException {
         super(length, couplingFront, couplingBack);
         if (identifier < 1) {
-            throw new InvalidInputException("coach id has to be positive!");
+            throw new LogicException("coach id has to be positive!");
         }
         this.identifier = identifier;
     }
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/DieselEngine.java b/src/edu/kit/informatik/modelrailwaysimulator/model/DieselEngine.java
index a154951..5a2b1ed 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/DieselEngine.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/DieselEngine.java
@@ -1,7 +1,5 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
-
 /**
  * Diesel engine.
  *
@@ -29,10 +27,10 @@ public class DieselEngine extends Engine {
      * @param length length of engine
      * @param couplingFront whether the engine should have a front coupling
      * @param couplingBack whether the engine should have a back coupling
-     * @throws InvalidInputException on invalid user input (e.g. zero-sized engine)
+     * @throws LogicException on invalid user input (e.g. zero-sized engine)
      */
     public DieselEngine(String series, String name, int length,
-                        boolean couplingFront, boolean couplingBack) throws InvalidInputException {
+                        boolean couplingFront, boolean couplingBack) throws LogicException {
         super(series, name, length, couplingFront, couplingBack);
     }
 
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/ElectricalEngine.java b/src/edu/kit/informatik/modelrailwaysimulator/model/ElectricalEngine.java
index b672096..2010389 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/ElectricalEngine.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/ElectricalEngine.java
@@ -1,7 +1,5 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
-
 /**
  * Electrical engine.
  *
@@ -31,10 +29,10 @@ public class ElectricalEngine extends Engine {
      * @param length length of engine
      * @param couplingFront whether the engine should have a front coupling
      * @param couplingBack whether the engine should have a back coupling
-     * @throws InvalidInputException on invalid user input (e.g. zero-sized engine)
+     * @throws LogicException on invalid user input (e.g. zero-sized engine)
      */
     public ElectricalEngine(String series, String name, int length, boolean couplingFront, boolean couplingBack)
-            throws InvalidInputException {
+            throws LogicException {
         super(series, name, length, couplingFront, couplingBack);
     }
 
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/Engine.java b/src/edu/kit/informatik/modelrailwaysimulator/model/Engine.java
index 63d058f..f98d653 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/Engine.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/Engine.java
@@ -1,7 +1,5 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
-
 /**
  * Generic engine, is usually either diesel, steam or electric.
  *
@@ -26,10 +24,10 @@ public abstract class Engine extends RollingStock {
      * @param length length of this engine
      * @param couplingFront whether this engine should have a front coupling
      * @param couplingBack whether this engine should have a back coupling
-     * @throws InvalidInputException on invalid user input (zero-sized coach)
+     * @throws LogicException on invalid user input (zero-sized coach)
      */
     protected Engine(String series, String name, int length,
-                     boolean couplingFront, boolean couplingBack) throws InvalidInputException {
+                     boolean couplingFront, boolean couplingBack) throws LogicException {
         super(length, couplingFront, couplingBack);
         this.series = series;
         this.name = name;
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/FreightCoach.java b/src/edu/kit/informatik/modelrailwaysimulator/model/FreightCoach.java
index 1288e43..07678b3 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/FreightCoach.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/FreightCoach.java
@@ -1,7 +1,5 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
-
 /**
  * A freight coach.
  *
@@ -27,10 +25,10 @@ public class FreightCoach extends Coach {
      * @param length length of coach
      * @param couplingFront whether the coach should have a front coupling
      * @param couplingBack whether the coach should have a back coupling
-     * @throws InvalidInputException on invalid user input (e.g. zero-sized coach)
+     * @throws LogicException on invalid user input (e.g. zero-sized coach)
      */
     public FreightCoach(int identifier, int length, boolean couplingFront, boolean couplingBack)
-            throws InvalidInputException {
+            throws LogicException {
         super(identifier, length, couplingFront, couplingBack);
     }
 
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/LogicException.java b/src/edu/kit/informatik/modelrailwaysimulator/model/LogicException.java
new file mode 100644
index 0000000..ad8763c
--- /dev/null
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/LogicException.java
@@ -0,0 +1,18 @@
+package edu.kit.informatik.modelrailwaysimulator.model;
+
+/**
+ * Thrown on illogical input or impossible to fulfill input.
+ *
+ * @author Arne Keller
+ * @version 1.0
+ */
+public class LogicException extends Exception {
+    /**
+     * Construct a new logic exception with a specific message.
+     *
+     * @param message the error message
+     */
+    public LogicException(String message) {
+        super(message);
+    }
+}
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/ModelRailwaySimulation.java b/src/edu/kit/informatik/modelrailwaysimulator/model/ModelRailwaySimulation.java
index 7b9e27c..887cf66 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/ModelRailwaySimulation.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/ModelRailwaySimulation.java
@@ -1,7 +1,6 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
 import edu.kit.informatik.modelrailwaysimulator.ui.CoachType;
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
 
 import java.util.List;
 import java.util.Map;
@@ -55,9 +54,9 @@ public class ModelRailwaySimulation {
      * @param start start position of the new track
      * @param end end position of the new track
      * @return the positive identifier of the new track if successful, -1 if none available
-     * @throws InvalidInputException if user input is invalid (e.g. zero length track)
+     * @throws LogicException if user input is invalid (e.g. zero length track)
      */
-    public int addTrack(Vector2D start, Vector2D end) throws InvalidInputException {
+    public int addTrack(Vector2D start, Vector2D end) throws LogicException {
         return railNetwork.addTrack(start, end);
     }
 
@@ -68,9 +67,9 @@ public class ModelRailwaySimulation {
      * @param end1 end position 1 of the switch
      * @param end2 end position 2 of the switch
      * @return the positive identifier of the switch if successful, -1 otherwise
-     * @throws InvalidInputException if the new switch would be invalid
+     * @throws LogicException if the new switch would be invalid
      */
-    public int addSwitch(Vector2D start, Vector2D end1, Vector2D end2) throws InvalidInputException {
+    public int addSwitch(Vector2D start, Vector2D end1, Vector2D end2) throws LogicException {
         return railNetwork.addSwitch(start, end1, end2);
     }
 
@@ -115,12 +114,12 @@ public class ModelRailwaySimulation {
      * Add a new engine to the simulation.
      *
      * @param newEngine the engine to add to the simulation
-     * @throws InvalidInputException when the identifier is already in use
+     * @throws LogicException when the identifier is already in use
      */
-    public void createEngine(Engine newEngine) throws InvalidInputException {
+    public void createEngine(Engine newEngine) throws LogicException {
         final String id = newEngine.getIdentifier();
         if (engines.containsKey(id) || trainSets.containsKey(id)) {
-            throw new InvalidInputException("engine identifier already used");
+            throw new LogicException("engine identifier already used");
         }
         engines.put(id, newEngine);
     }
@@ -147,10 +146,10 @@ public class ModelRailwaySimulation {
      * @param couplingFront whether the coach should have a front coupling
      * @param couplingBack whether the coach should have a back coupling
      * @return the identifier of the coach if successfully added, -1 if none available
-     * @throws InvalidInputException if user input is invalid (e.g. zero-sized coach)
+     * @throws LogicException if user input is invalid (e.g. zero-sized coach)
      */
     public int createCoach(CoachType coachType, int length,
-                           boolean couplingFront, boolean couplingBack) throws InvalidInputException {
+                           boolean couplingFront, boolean couplingBack) throws LogicException {
         final int id = getNextCoachIdentifier();
         if (id < 0) {
             return -1;
@@ -189,12 +188,12 @@ public class ModelRailwaySimulation {
      * Add a new train set to the simulation.
      *
      * @param newTrainSet the train set to add
-     * @throws InvalidInputException if the identifier is already used
+     * @throws LogicException if the identifier is already used
      */
-    public void createTrainSet(TrainSet newTrainSet) throws InvalidInputException {
+    public void createTrainSet(TrainSet newTrainSet) throws LogicException {
         final String id = newTrainSet.getIdentifier();
         if (engines.containsKey(id) || trainSets.containsKey(id)) {
-            throw new InvalidInputException("train set identifier already used");
+            throw new LogicException("train set identifier already used");
         }
         trainSets.put(id, newTrainSet);
     }
@@ -258,13 +257,13 @@ public class ModelRailwaySimulation {
      * @param trainId identifier of the train
      * @param rollingStockId identifier of the rolling stock
      * @return the added rolling stock
-     * @throws InvalidInputException if train not found and train identifier is not next identifier or rolling stock
+     * @throws LogicException if train not found and train identifier is not next identifier or rolling stock
      *  is not found
      */
-    public RollingStock addTrain(int trainId, String rollingStockId) throws InvalidInputException {
+    public RollingStock addTrain(int trainId, String rollingStockId) throws LogicException {
         final Optional<RollingStock> rollingStock = getRollingStock(rollingStockId);
         if (!rollingStock.isPresent()) {
-            throw new InvalidInputException("rolling stock not found");
+            throw new LogicException("rolling stock not found");
         }
         trainManager.addTrain(trainId, rollingStock.get());
         return rollingStock.get();
@@ -304,9 +303,9 @@ public class ModelRailwaySimulation {
      *
      * @param id identifier of the train to show
      * @return rows of ASCII art representing this train
-     * @throws InvalidInputException if train not found
+     * @throws LogicException if train not found
      */
-    public List<String> showTrain(int id) throws InvalidInputException {
+    public List<String> showTrain(int id) throws LogicException {
         return trainManager.showTrain(id);
     }
 
@@ -317,10 +316,10 @@ public class ModelRailwaySimulation {
      * @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 if train could not be found, is already placed, is not valid, direction is invalid
+     * @throws LogicException if train could not be found, is already placed, is not valid, direction is invalid
      *  or railway network is not ready for trains
      */
-    public boolean putTrain(int trainId, Vector2D position, Vector2D direction) throws InvalidInputException {
+    public boolean putTrain(int trainId, Vector2D position, Vector2D direction) throws LogicException {
         return trainManager.putTrain(trainId, position, direction);
     }
 
@@ -329,9 +328,9 @@ public class ModelRailwaySimulation {
      *
      * @param speed amount of steps to move the trains
      * @return train collisions, no value if no trains are placed
-     * @throws InvalidInputException if the simulation is not yet ready
+     * @throws LogicException if the simulation is not yet ready
      */
-    public Optional<List<SortedSet<Integer>>> step(short speed) throws InvalidInputException {
+    public Optional<List<SortedSet<Integer>>> step(short speed) throws LogicException {
         return trainManager.step(speed);
     }
 }
\ No newline at end of file
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/PassengerCoach.java b/src/edu/kit/informatik/modelrailwaysimulator/model/PassengerCoach.java
index c64aceb..37428f2 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/PassengerCoach.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/PassengerCoach.java
@@ -1,7 +1,5 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
-
 /**
  * A passenger coach.
  *
@@ -28,10 +26,10 @@ public class PassengerCoach extends Coach {
      * @param length length of coach
      * @param couplingFront whether the coach should have a front coupling
      * @param couplingBack whether the coach should have a back coupling
-     * @throws InvalidInputException on invalid user input (e.g. zero-sized coach)
+     * @throws LogicException on invalid user input (e.g. zero-sized coach)
      */
     public PassengerCoach(int identifier, int length, boolean couplingFront, boolean couplingBack)
-            throws InvalidInputException {
+            throws LogicException {
         super(identifier, length, couplingFront, couplingBack);
     }
 
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/RailwayNetwork.java b/src/edu/kit/informatik/modelrailwaysimulator/model/RailwayNetwork.java
index 96d6ca5..cf45eed 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/RailwayNetwork.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/RailwayNetwork.java
@@ -1,7 +1,5 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
-
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedList;
@@ -31,13 +29,13 @@ public class RailwayNetwork {
      * @param start start position of the new track
      * @param end end position of the new track
      * @return the positive identifier of the new track if successful, -1 if none available
-     * @throws InvalidInputException if the user provides incorrect input
+     * @throws LogicException if the user provides incorrect input
      */
-    public int addTrack(Vector2D start, Vector2D end) throws InvalidInputException {
+    public int addTrack(Vector2D start, Vector2D end) throws LogicException {
         final long startPossibleConnections = rails.values().stream().filter(rail -> rail.canConnectTo(start)).count();
         final long endPossibleConnections = rails.values().stream().filter(rail -> rail.canConnectTo(end)).count();
         if (startPossibleConnections == 2 || endPossibleConnections == 2) {
-            throw new InvalidInputException("track would connect to two other rails");
+            throw new LogicException("track would connect to two other rails");
         }
         if (rails.isEmpty()) {
             final Track newTrack = new Track(start, end, 1);
@@ -53,7 +51,7 @@ public class RailwayNetwork {
                 rails.put(id, newTrack);
                 return newTrack.getIdentifier();
             } else {
-                throw new InvalidInputException("track is not connected to other tracks");
+                throw new LogicException("track is not connected to other tracks");
             }
         }
     }
@@ -65,9 +63,9 @@ public class RailwayNetwork {
      * @param end1 end position 1 of the switch
      * @param end2 end position 2 of the switch
      * @return the positive identifier of the switch if successful, -1 otherwise
-     * @throws InvalidInputException when the new switch would be invalid
+     * @throws LogicException when the new switch would be invalid
      */
-    public int addSwitch(Vector2D start, Vector2D end1, Vector2D end2) throws InvalidInputException {
+    public int addSwitch(Vector2D start, Vector2D end1, Vector2D end2) throws LogicException {
         if (rails.isEmpty()) {
             final Switch newSwitch = new Switch(start, end1, end2, 1);
             rails.put(1, newSwitch);
@@ -77,7 +75,7 @@ public class RailwayNetwork {
             final long end1Connections = rails.values().stream().filter(rail -> rail.canConnectTo(end1)).count();
             final long end2Connections = rails.values().stream().filter(rail -> rail.canConnectTo(end2)).count();
             if (startConnections == 2 || end1Connections == 2 || end2Connections == 2) {
-                throw new InvalidInputException("switch endpoint would connect to two other rails");
+                throw new LogicException("switch endpoint would connect to two other rails");
             }
             if (rails.values().stream()
                     .anyMatch(rail -> rail.canConnectTo(start) || rail.canConnectTo(end1) || rail.canConnectTo(end2))) {
@@ -89,7 +87,7 @@ public class RailwayNetwork {
                 rails.put(id, newSwitch);
                 return newSwitch.getIdentifier();
             } else {
-                throw new InvalidInputException("switch not connected to other rails");
+                throw new LogicException("switch not connected to other rails");
             }
         }
     }
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/RollingStock.java b/src/edu/kit/informatik/modelrailwaysimulator/model/RollingStock.java
index 0a459c8..7b7871e 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/RollingStock.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/RollingStock.java
@@ -1,7 +1,5 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
-
 /**
  * A rolling stock with a specific integer length and couplings. Is usually an engine, train set or coach.
  *
@@ -28,14 +26,14 @@ public abstract class RollingStock {
      * @param length length of this rolling stock
      * @param couplingFront whether this rolling stock should have a front coupling
      * @param couplingBack whether this rolling stock should have a back coupling
-     * @throws InvalidInputException on invalid user input (e.g. zero-sized coach)
+     * @throws LogicException on invalid user input (e.g. zero-sized coach)
      */
-    protected RollingStock(int length, boolean couplingFront, boolean couplingBack) throws InvalidInputException {
+    protected RollingStock(int length, boolean couplingFront, boolean couplingBack) throws LogicException {
         if (length < 1) {
-            throw new InvalidInputException("rolling stock length has to be positive");
+            throw new LogicException("rolling stock length has to be positive");
         }
         if (!couplingFront && !couplingBack) {
-            throw new InvalidInputException("rolling stocks needs at least one coupling");
+            throw new LogicException("rolling stocks needs at least one coupling");
         }
         this.length = length;
         this.couplingFront = couplingFront;
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/SpecialCoach.java b/src/edu/kit/informatik/modelrailwaysimulator/model/SpecialCoach.java
index 615e4cd..a43b75e 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/SpecialCoach.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/SpecialCoach.java
@@ -1,7 +1,5 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
-
 /**
  * A special coach, used for e.g. firefighting.
  *
@@ -29,10 +27,10 @@ public class SpecialCoach extends Coach {
      * @param length length of coach
      * @param couplingFront whether the coach should have a front coupling
      * @param couplingBack whether the coach should have a back coupling
-     * @throws InvalidInputException on invalid user input (e.g. zero-sized coach)
+     * @throws LogicException on invalid user input (e.g. zero-sized coach)
      */
     public SpecialCoach(int identifier, int length, boolean couplingFront, boolean couplingBack)
-            throws InvalidInputException {
+            throws LogicException {
         super(identifier, length, couplingFront, couplingBack);
     }
 
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/SteamEngine.java b/src/edu/kit/informatik/modelrailwaysimulator/model/SteamEngine.java
index 634758d..ddb2376 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/SteamEngine.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/SteamEngine.java
@@ -1,7 +1,5 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
-
 /**
  * Steam engine.
  *
@@ -29,10 +27,10 @@ public class SteamEngine extends Engine {
      * @param length length of engine
      * @param couplingFront whether the engine should have a front coupling
      * @param couplingBack whether the engine should have a back coupling
-     * @throws InvalidInputException on invalid user input (e.g. zero-sized engine)
+     * @throws LogicException on invalid user input (e.g. zero-sized engine)
      */
     public SteamEngine(String series, String name, int length, boolean couplingFront, boolean couplingBack)
-            throws InvalidInputException {
+            throws LogicException {
         super(series, name, length, couplingFront, couplingBack);
     }
 
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/Switch.java b/src/edu/kit/informatik/modelrailwaysimulator/model/Switch.java
index 83d1c45..2a84432 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/Switch.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/Switch.java
@@ -1,7 +1,5 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
-
 import java.util.Objects;
 
 /**
@@ -31,12 +29,12 @@ public final class Switch extends Rail {
      * @param end1 first end position
      * @param end2 second end position
      * @param id identifier of this switch
-     * @throws InvalidInputException if the switch is not composed of straight lines, or has zero-length parts
+     * @throws LogicException if the switch is not composed of straight lines, or has zero-length parts
      */
-    public Switch(Vector2D start, Vector2D end1, Vector2D end2, int id) throws InvalidInputException {
+    public Switch(Vector2D start, Vector2D end1, Vector2D end2, int id) throws LogicException {
         super(id);
         if (start.distanceTo(end1) == 0 || start.distanceTo(end2) == 0 || end1.distanceTo(end2) == 0) {
-            throw new InvalidInputException("switch has length zero");
+            throw new LogicException("switch has length zero");
         }
         this.positionOne = new Track(start, end1, 1);
         this.positionTwo = new Track(start, end2, 1);
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/Track.java b/src/edu/kit/informatik/modelrailwaysimulator/model/Track.java
index 18ea5a4..6be8ee5 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/Track.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/Track.java
@@ -1,7 +1,5 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
-
 import java.util.Objects;
 
 /**
@@ -26,14 +24,14 @@ public final class Track extends Rail {
      * @param start start position of the track
      * @param end end position of the track
      * @param id identifier to use
-     * @throws InvalidInputException if the positions are not on a straight line
+     * @throws LogicException if the positions are not on a straight line
      */
-    public Track(Vector2D start, Vector2D end, int id) throws InvalidInputException {
+    public Track(Vector2D start, Vector2D end, int id) throws LogicException {
         super(id);
         if (start.distanceTo(end) == 0) {
-            throw new InvalidInputException("track has length zero");
+            throw new LogicException("track has length zero");
         } else if (start.getX() != end.getX() && start.getY() != end.getY()) {
-            throw new InvalidInputException("invalid track segment: not a straight line");
+            throw new LogicException("invalid track segment: not a straight line");
         }
         this.start = start;
         this.end = end;
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/Train.java b/src/edu/kit/informatik/modelrailwaysimulator/model/Train.java
index bc2023f..cbca23f 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/Train.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/Train.java
@@ -1,7 +1,5 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
-
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashSet;
@@ -76,16 +74,16 @@ public final class Train implements Comparable<Train> {
      * Add a rolling stock to this train.
      *
      * @param rollingStock the rolling stack to add
-     * @throws InvalidInputException if the rolling stock could not be added to the train
+     * @throws LogicException if the rolling stock could not be added to the train
      */
-    public void add(RollingStock rollingStock) throws InvalidInputException {
+    public void add(RollingStock rollingStock) throws LogicException {
         final RollingStock last = rollingStocks.get(rollingStocks.size() - 1);
         // make sure special coupling requirements are honored
         if (rollingStock.hasCouplingFront() && last.hasCouplingBack()
                 && rollingStock.canCoupleTo(last) && last.canCoupleTo(rollingStock)) {
             rollingStocks.add(rollingStock);
         } else {
-            throw new InvalidInputException("could not add rolling stock to train");
+            throw new LogicException("could not add rolling stock to train");
         }
     }
 
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/TrainManager.java b/src/edu/kit/informatik/modelrailwaysimulator/model/TrainManager.java
index 2d0232c..74cacad 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/TrainManager.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/TrainManager.java
@@ -1,7 +1,5 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
-
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Comparator;
@@ -77,23 +75,23 @@ public final class TrainManager {
      *
      * @param trainId train identifier
      * @param rollingStock rolling stock to add
-     * @throws InvalidInputException on invalid user input (e.g. rolling stock in use)
+     * @throws LogicException on invalid user input (e.g. rolling stock in use)
      */
-    public void addTrain(int trainId, RollingStock rollingStock) throws InvalidInputException {
+    public void addTrain(int trainId, RollingStock rollingStock) throws LogicException {
         if (getTrainContainingRollingStock(rollingStock).isPresent()) {
-            throw new InvalidInputException("rolling stock already used");
+            throw new LogicException("rolling stock already used");
         }
         final Train train = trains.get(trainId);
         if (train == null) { // create new train
             final int correctId = getNextTrainIdentifier();
             if (trainId != correctId) {
-                throw new InvalidInputException("new train identifier must be next free identifier");
+                throw new LogicException("new train identifier must be next free identifier");
             }
             final Train newTrain = new Train(trainId, rollingStock);
             trains.put(trainId, newTrain);
         } else {
             if (train.isPlaced()) {
-                throw new InvalidInputException("can not add rolling stock to placed train");
+                throw new LogicException("can not add rolling stock to placed train");
             }
             train.add(rollingStock);
         }
@@ -139,14 +137,14 @@ public final class TrainManager {
      *
      * @param trainId identifier of the train to show
      * @return ASCII art representation of said train
-     * @throws InvalidInputException if train not found
+     * @throws LogicException if train not found
      */
-    public List<String> showTrain(int trainId) throws InvalidInputException {
+    public List<String> showTrain(int trainId) throws LogicException {
         final Train train = trains.get(trainId);
         if (train != null) {
             return train.show();
         } else {
-            throw new InvalidInputException("no such train");
+            throw new LogicException("no such train");
         }
     }
 
@@ -158,21 +156,21 @@ public final class TrainManager {
      * @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 if train could not be found, is already placed, is not valid, direction is invalid
+     * @throws LogicException if train could not be found, is already placed, is not valid, direction is invalid
      *  or railway network is not ready for trains
      */
-    public boolean putTrain(int trainId, Vector2D position, Vector2D direction) throws InvalidInputException {
+    public boolean putTrain(int trainId, Vector2D position, Vector2D direction) throws LogicException {
         final Train train = trains.get(trainId);
         if (train == null) {
-            throw new InvalidInputException("train not found");
+            throw new LogicException("train not found");
         } else if (!train.isProperTrain()) {
-            throw new InvalidInputException("train is not valid");
+            throw new LogicException("train is not valid");
         } else if (train.isPlaced()) {
-            throw new InvalidInputException("train is already placed");
+            throw new LogicException("train is already placed");
         } else if (!direction.isDirection()) {
-            throw new InvalidInputException("invalid train direction");
+            throw new LogicException("invalid train direction");
         } else if (!railNetwork.isReadyForTrains()) {
-            throw new InvalidInputException("switches not set up");
+            throw new LogicException("switches not set up");
         }
         // attempt to place train
         final boolean placed = train.placeOn(railNetwork, position, direction);
@@ -305,11 +303,11 @@ public final class TrainManager {
      *
      * @param speed amount of steps to move the trains
      * @return train collisions, no value if no trains are placed
-     * @throws InvalidInputException if simulation is not yet ready
+     * @throws LogicException if simulation is not yet ready
      */
-    public Optional<List<SortedSet<Integer>>> step(short speed) throws InvalidInputException {
+    public Optional<List<SortedSet<Integer>>> step(short speed) throws LogicException {
         if (!railNetwork.isReadyForTrains()) {
-            throw new InvalidInputException("rail tracks/switches not set up");
+            throw new LogicException("rail tracks/switches not set up");
         }
         if (trains.values().stream().noneMatch(Train::isPlaced)) {
             return Optional.empty();
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/model/TrainSet.java b/src/edu/kit/informatik/modelrailwaysimulator/model/TrainSet.java
index c60634b..ccb2673 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/model/TrainSet.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/model/TrainSet.java
@@ -1,7 +1,5 @@
 package edu.kit.informatik.modelrailwaysimulator.model;
 
-import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
-
 /**
  * Train set.
  *
@@ -40,10 +38,10 @@ public class TrainSet extends RollingStock {
      * @param length length of train set
      * @param couplingFront whether the train set should have a front coupling
      * @param couplingBack whether the train set should have a back coupling
-     * @throws InvalidInputException on invalid user input (e.g. zero-sized train set)
+     * @throws LogicException on invalid user input (e.g. zero-sized train set)
      */
     public TrainSet(String series, String name, int length, boolean couplingFront, boolean couplingBack)
-            throws InvalidInputException {
+            throws LogicException {
         super(length, couplingFront, couplingBack);
         this.name = name;
         this.series = series;
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/ui/CoachType.java b/src/edu/kit/informatik/modelrailwaysimulator/ui/CoachType.java
index ca4bcd6..ee27442 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/ui/CoachType.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/ui/CoachType.java
@@ -2,6 +2,7 @@ package edu.kit.informatik.modelrailwaysimulator.ui;
 
 import edu.kit.informatik.modelrailwaysimulator.model.Coach;
 import edu.kit.informatik.modelrailwaysimulator.model.FreightCoach;
+import edu.kit.informatik.modelrailwaysimulator.model.LogicException;
 import edu.kit.informatik.modelrailwaysimulator.model.PassengerCoach;
 import edu.kit.informatik.modelrailwaysimulator.model.SpecialCoach;
 
@@ -38,10 +39,10 @@ public enum CoachType {
      * @param couplingFront whether the coach should have a front coupling
      * @param couplingBack whether the coach should have a back coupling
      * @return new coach
-     * @throws InvalidInputException on invalid input (e.g. zero-sized coach)
+     * @throws LogicException on invalid input (e.g. zero-sized coach)
      */
     public Coach createCoach(int id, int length, boolean couplingFront, boolean couplingBack)
-            throws InvalidInputException {
+            throws LogicException {
         switch (this) {
             case PASSENGER:
                 return new PassengerCoach(id, length, couplingFront, couplingBack);
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/ui/CommandLine.java b/src/edu/kit/informatik/modelrailwaysimulator/ui/CommandLine.java
index 29863ad..ee4823b 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/ui/CommandLine.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/ui/CommandLine.java
@@ -1,7 +1,9 @@
 package edu.kit.informatik.modelrailwaysimulator.ui;
 
+import edu.kit.informatik.modelrailwaysimulator.model.LogicException;
 import edu.kit.informatik.modelrailwaysimulator.model.ModelRailwaySimulation;
 import edu.kit.informatik.Terminal;
+import edu.kit.informatik.modelrailwaysimulator.ui.command.Command;
 import edu.kit.informatik.modelrailwaysimulator.ui.command.CommandFactory;
 
 /**
@@ -46,10 +48,17 @@ public final class CommandLine {
                 }
             }
 
+            final Command command;
             try {
-                CommandFactory.getCommand(input).apply(simulation);
+                command = CommandFactory.getCommand(input);
             } catch (final NumberFormatException | InvalidInputException e) {
-                Terminal.printError(e.getMessage());
+                Terminal.printError("input error: " + e.getMessage());
+                continue;
+            }
+            try {
+                command.apply(simulation);
+            } catch (final NumberFormatException | LogicException e) {
+                Terminal.printError("logic error: " + e.getMessage());
             }
         }
     }
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/ui/EngineType.java b/src/edu/kit/informatik/modelrailwaysimulator/ui/EngineType.java
index b6027dc..dba29e4 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/ui/EngineType.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/ui/EngineType.java
@@ -3,6 +3,7 @@ package edu.kit.informatik.modelrailwaysimulator.ui;
 import edu.kit.informatik.modelrailwaysimulator.model.DieselEngine;
 import edu.kit.informatik.modelrailwaysimulator.model.ElectricalEngine;
 import edu.kit.informatik.modelrailwaysimulator.model.Engine;
+import edu.kit.informatik.modelrailwaysimulator.model.LogicException;
 import edu.kit.informatik.modelrailwaysimulator.model.SteamEngine;
 
 /**
@@ -39,10 +40,10 @@ public enum EngineType {
      * @param couplingFront whether the engine should have a front coupling
      * @param couplingBack whether the engine should have a back coupling
      * @return new engine
-     * @throws InvalidInputException on invalid input (e.g. zero-sized engine)
+     * @throws LogicException on invalid input (e.g. zero-sized engine)
      */
     public Engine createEngine(String series, String name, int length, boolean couplingFront, boolean couplingBack)
-            throws InvalidInputException {
+            throws LogicException {
         switch (this) {
             case ELECTRICAL:
                 return new ElectricalEngine(series, name, length, couplingFront, couplingBack);
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/AddSwitch.java b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/AddSwitch.java
index 2149b9d..fa84862 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/AddSwitch.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/AddSwitch.java
@@ -1,5 +1,6 @@
 package edu.kit.informatik.modelrailwaysimulator.ui.command;
 
+import edu.kit.informatik.modelrailwaysimulator.model.LogicException;
 import edu.kit.informatik.modelrailwaysimulator.model.ModelRailwaySimulation;
 import edu.kit.informatik.modelrailwaysimulator.model.Vector2D;
 import edu.kit.informatik.Terminal;
@@ -38,7 +39,7 @@ public class AddSwitch extends Command {
     private Vector2D end2;
 
     @Override
-    public void apply(ModelRailwaySimulation simulation) throws InvalidInputException {
+    public void apply(ModelRailwaySimulation simulation) throws LogicException {
         if (start == null) {
             throw new IllegalStateException("command not initialized");
         }
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/AddTrack.java b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/AddTrack.java
index 03002df..13d18ba 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/AddTrack.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/AddTrack.java
@@ -1,5 +1,6 @@
 package edu.kit.informatik.modelrailwaysimulator.ui.command;
 
+import edu.kit.informatik.modelrailwaysimulator.model.LogicException;
 import edu.kit.informatik.modelrailwaysimulator.model.ModelRailwaySimulation;
 import edu.kit.informatik.modelrailwaysimulator.model.Vector2D;
 import edu.kit.informatik.Terminal;
@@ -34,7 +35,7 @@ public class AddTrack extends Command {
     private Vector2D end;
 
     @Override
-    public void apply(ModelRailwaySimulation simulation) throws InvalidInputException {
+    public void apply(ModelRailwaySimulation simulation) throws LogicException {
         if (start == null) {
             throw new IllegalStateException("command not initialized");
         }
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/AddTrain.java b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/AddTrain.java
index 344a5b0..a2c8a5f 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/AddTrain.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/AddTrain.java
@@ -1,5 +1,6 @@
 package edu.kit.informatik.modelrailwaysimulator.ui.command;
 
+import edu.kit.informatik.modelrailwaysimulator.model.LogicException;
 import edu.kit.informatik.modelrailwaysimulator.model.ModelRailwaySimulation;
 import edu.kit.informatik.modelrailwaysimulator.model.RollingStock;
 import edu.kit.informatik.Terminal;
@@ -35,7 +36,7 @@ public class AddTrain extends Command {
     private String rollingStockId;
 
     @Override
-    public void apply(ModelRailwaySimulation simulation) throws InvalidInputException {
+    public void apply(ModelRailwaySimulation simulation) throws LogicException {
         if (rollingStockId == null) {
             throw new IllegalStateException("command not initialized");
         }
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/Command.java b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/Command.java
index 126d26a..9b5753c 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/Command.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/Command.java
@@ -1,5 +1,6 @@
 package edu.kit.informatik.modelrailwaysimulator.ui.command;
 
+import edu.kit.informatik.modelrailwaysimulator.model.LogicException;
 import edu.kit.informatik.modelrailwaysimulator.model.ModelRailwaySimulation;
 import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
 
@@ -15,9 +16,9 @@ public abstract class Command {
      * Apply this command to a model railway simulation.
      *
      * @param simulation simulation to use
-     * @throws InvalidInputException on invalid user input
+     * @throws LogicException on illogical user input
      */
-    public abstract void apply(ModelRailwaySimulation simulation) throws InvalidInputException;
+    public abstract void apply(ModelRailwaySimulation simulation) throws LogicException;
 
     /**
      * Parse user input into this command object.
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/CreateCoach.java b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/CreateCoach.java
index 51a82a0..d8fb070 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/CreateCoach.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/CreateCoach.java
@@ -1,5 +1,6 @@
 package edu.kit.informatik.modelrailwaysimulator.ui.command;
 
+import edu.kit.informatik.modelrailwaysimulator.model.LogicException;
 import edu.kit.informatik.modelrailwaysimulator.ui.CoachType;
 import edu.kit.informatik.modelrailwaysimulator.model.ModelRailwaySimulation;
 import edu.kit.informatik.Terminal;
@@ -44,7 +45,7 @@ public class CreateCoach extends Command {
     private boolean couplingBack;
 
     @Override
-    public void apply(ModelRailwaySimulation simulation) throws InvalidInputException {
+    public void apply(ModelRailwaySimulation simulation) throws LogicException {
         if (type == null) {
             throw new IllegalStateException("command not initialized");
         }
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/CreateEngine.java b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/CreateEngine.java
index 45ac8da..4922659 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/CreateEngine.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/CreateEngine.java
@@ -3,6 +3,7 @@ package edu.kit.informatik.modelrailwaysimulator.ui.command;
 import edu.kit.informatik.Terminal;
 import edu.kit.informatik.modelrailwaysimulator.model.Coach;
 import edu.kit.informatik.modelrailwaysimulator.model.Engine;
+import edu.kit.informatik.modelrailwaysimulator.model.LogicException;
 import edu.kit.informatik.modelrailwaysimulator.model.ModelRailwaySimulation;
 import edu.kit.informatik.modelrailwaysimulator.ui.EngineType;
 import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
@@ -56,7 +57,7 @@ public class CreateEngine extends Command {
     private boolean couplingBack;
 
     @Override
-    public void apply(ModelRailwaySimulation simulation) throws InvalidInputException {
+    public void apply(ModelRailwaySimulation simulation) throws LogicException {
         if (type == null) {
             throw new IllegalStateException("command not initialized");
         }
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/CreateTrainSet.java b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/CreateTrainSet.java
index 503bc39..12363ce 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/CreateTrainSet.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/CreateTrainSet.java
@@ -1,6 +1,7 @@
 package edu.kit.informatik.modelrailwaysimulator.ui.command;
 
 import edu.kit.informatik.modelrailwaysimulator.model.Coach;
+import edu.kit.informatik.modelrailwaysimulator.model.LogicException;
 import edu.kit.informatik.modelrailwaysimulator.model.ModelRailwaySimulation;
 import edu.kit.informatik.Terminal;
 import edu.kit.informatik.modelrailwaysimulator.model.TrainSet;
@@ -50,7 +51,7 @@ public class CreateTrainSet extends Command {
     private boolean couplingBack;
 
     @Override
-    public void apply(ModelRailwaySimulation simulation) throws InvalidInputException {
+    public void apply(ModelRailwaySimulation simulation) throws LogicException {
         if (name == null) {
             throw new IllegalStateException("command not initialized");
         }
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/PutTrain.java b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/PutTrain.java
index fd52a90..9482b54 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/PutTrain.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/PutTrain.java
@@ -1,5 +1,6 @@
 package edu.kit.informatik.modelrailwaysimulator.ui.command;
 
+import edu.kit.informatik.modelrailwaysimulator.model.LogicException;
 import edu.kit.informatik.modelrailwaysimulator.model.ModelRailwaySimulation;
 import edu.kit.informatik.modelrailwaysimulator.model.Vector2D;
 import edu.kit.informatik.Terminal;
@@ -40,7 +41,7 @@ public class PutTrain extends Command {
     private Vector2D direction;
 
     @Override
-    public void apply(ModelRailwaySimulation simulation) throws InvalidInputException {
+    public void apply(ModelRailwaySimulation simulation) throws LogicException {
         if (point == null) {
             throw new IllegalStateException("command not initialized");
         }
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/ShowTrain.java b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/ShowTrain.java
index 32f4561..970a31f 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/ShowTrain.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/ShowTrain.java
@@ -1,6 +1,7 @@
 package edu.kit.informatik.modelrailwaysimulator.ui.command;
 
 import edu.kit.informatik.Terminal;
+import edu.kit.informatik.modelrailwaysimulator.model.LogicException;
 import edu.kit.informatik.modelrailwaysimulator.model.ModelRailwaySimulation;
 import edu.kit.informatik.modelrailwaysimulator.ui.InvalidInputException;
 
@@ -24,7 +25,7 @@ public class ShowTrain extends Command {
     private int id;
 
     @Override
-    public void apply(ModelRailwaySimulation simulation) throws InvalidInputException {
+    public void apply(ModelRailwaySimulation simulation) throws LogicException {
         simulation.showTrain(id).forEach(Terminal::printLine);
     }
 
diff --git a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/Step.java b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/Step.java
index 40a45bb..5f84af0 100644
--- a/src/edu/kit/informatik/modelrailwaysimulator/ui/command/Step.java
+++ b/src/edu/kit/informatik/modelrailwaysimulator/ui/command/Step.java
@@ -1,6 +1,7 @@
 package edu.kit.informatik.modelrailwaysimulator.ui.command;
 
 import edu.kit.informatik.Terminal;
+import edu.kit.informatik.modelrailwaysimulator.model.LogicException;
 import edu.kit.informatik.modelrailwaysimulator.model.ModelRailwaySimulation;
 import edu.kit.informatik.modelrailwaysimulator.model.Vector2D;
 import edu.kit.informatik.modelrailwaysimulator.ui.CommandLine;
@@ -30,7 +31,7 @@ public class Step extends Command {
     private short speed;
 
     @Override
-    public void apply(ModelRailwaySimulation simulation) throws InvalidInputException {
+    public void apply(ModelRailwaySimulation simulation) throws LogicException {
         final Optional<List<SortedSet<Integer>>> collisions = simulation.step(speed);
         if (!collisions.isPresent()) {
             // print OK if no there are trains placed