diff --git a/basics_output.txt b/basics_output.txt
index b8c4bfb..39e755a 100644
--- a/basics_output.txt
+++ b/basics_output.txt
@@ -8,7 +8,7 @@ OK
 t 1 (0,0) -> (-5,0) 5
 t 2 (-5,0) -> (-5,5) 5
 s 3 (0,5) -> (0,0),(-5,5) 5
-Error, track is not connected to other tracks
+Error, track would connect to two other rails
 A-B
 train-set A-B added to train 1
 OK
diff --git a/fuzz4_output.txt b/fuzz4_output.txt
index 3af0857..02a814a 100644
--- a/fuzz4_output.txt
+++ b/fuzz4_output.txt
@@ -1,9 +1,9 @@
-Error, track has length 0
+Error, track has length zero
 1
 2
 3
 4
-Error, track is not connected to other tracks
+Error, track would connect to two other rails
 T3-Emma
 1
 2
diff --git a/src/edu/kit/informatik/model/Coach.java b/src/edu/kit/informatik/model/Coach.java
index 977a1d0..1e5550c 100644
--- a/src/edu/kit/informatik/model/Coach.java
+++ b/src/edu/kit/informatik/model/Coach.java
@@ -1,6 +1,7 @@
 package edu.kit.informatik.model;
 
 import edu.kit.informatik.ui.CoachType;
+import edu.kit.informatik.ui.InvalidInputException;
 
 /**
  * A coach.
@@ -61,9 +62,10 @@ public 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 (zero-sized coach)
      */
     public Coach(final int identifier, final CoachType type, final int length,
-                 final boolean couplingFront, final boolean couplingBack) {
+                 final boolean couplingFront, final boolean couplingBack) throws InvalidInputException {
         super(length, couplingFront, couplingBack);
         this.identifier = identifier;
         this.type = type;
diff --git a/src/edu/kit/informatik/model/DieselEngine.java b/src/edu/kit/informatik/model/DieselEngine.java
index 5a8f4e5..700d655 100644
--- a/src/edu/kit/informatik/model/DieselEngine.java
+++ b/src/edu/kit/informatik/model/DieselEngine.java
@@ -1,5 +1,7 @@
 package edu.kit.informatik.model;
 
+import edu.kit.informatik.ui.InvalidInputException;
+
 /**
  * Diesel engine.
  *
@@ -26,9 +28,10 @@ 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)
      */
     public DieselEngine(final String series, final String name, final int length,
-                        final boolean couplingFront, final boolean couplingBack) {
+                        final boolean couplingFront, final boolean couplingBack) throws InvalidInputException {
         super(series, name, length, couplingFront, couplingBack);
     }
 
diff --git a/src/edu/kit/informatik/model/ElectricalEngine.java b/src/edu/kit/informatik/model/ElectricalEngine.java
index 4040332..0e3ab51 100644
--- a/src/edu/kit/informatik/model/ElectricalEngine.java
+++ b/src/edu/kit/informatik/model/ElectricalEngine.java
@@ -1,5 +1,7 @@
 package edu.kit.informatik.model;
 
+import edu.kit.informatik.ui.InvalidInputException;
+
 /**
  * Electrical engine.
  *
@@ -28,9 +30,10 @@ 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)
      */
     public ElectricalEngine(final String series, final String name, final int length,
-                            final boolean couplingFront, final boolean couplingBack) {
+                            final boolean couplingFront, final boolean couplingBack) throws InvalidInputException {
         super(series, name, length, couplingFront, couplingBack);
     }
 
diff --git a/src/edu/kit/informatik/model/Engine.java b/src/edu/kit/informatik/model/Engine.java
index 0dd26e0..3243c5e 100644
--- a/src/edu/kit/informatik/model/Engine.java
+++ b/src/edu/kit/informatik/model/Engine.java
@@ -1,5 +1,7 @@
 package edu.kit.informatik.model;
 
+import edu.kit.informatik.ui.InvalidInputException;
+
 /**
  * Generic engine, is usually either diesel, steam or electric.
  *
@@ -10,14 +12,23 @@ public abstract class Engine extends RollingStock {
     /**
      * Series/class of this engine.
      */
-    private String series;
+    private final String series;
     /**
      * Name of this engine.
      */
-    private String name;
+    private final String name;
 
+    /**
+     * Initialize an engine.
+     * @param series series/class of this engine
+     * @param name name of this engine
+     * @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)
+     */
     protected Engine(final String series, final String name,  final int length,
-                     final boolean couplingFront, final boolean couplingBack) {
+                     final boolean couplingFront, final boolean couplingBack) throws InvalidInputException {
         super(length, couplingFront, couplingBack);
         this.series = series;
         this.name = name;
diff --git a/src/edu/kit/informatik/model/ModelRailwaySimulation.java b/src/edu/kit/informatik/model/ModelRailwaySimulation.java
index 7930f9c..21e5109 100644
--- a/src/edu/kit/informatik/model/ModelRailwaySimulation.java
+++ b/src/edu/kit/informatik/model/ModelRailwaySimulation.java
@@ -46,9 +46,10 @@ public class ModelRailwaySimulation {
      * Add a new track to the rail network of this simulation.
      * @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 otherwise
+     * @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)
      */
-    public int addTrack(final Vector2D start, final Vector2D end) {
+    public int addTrack(final Vector2D start, final Vector2D end) throws InvalidInputException {
         return railNetwork.addTrack(start, end);
     }
 
@@ -146,10 +147,11 @@ public class ModelRailwaySimulation {
      * @param length length of the coach
      * @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 otherwise
+     * @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)
      */
     public int createCoach(final CoachType coachType, final int length,
-                           final boolean couplingFront, final boolean couplingBack) {
+                           final boolean couplingFront, final boolean couplingBack) throws InvalidInputException {
         int id = getNextCoachIdentifier();
         if (id < 0) {
             return -1;
diff --git a/src/edu/kit/informatik/model/RailwayNetwork.java b/src/edu/kit/informatik/model/RailwayNetwork.java
index f818624..805bfa8 100644
--- a/src/edu/kit/informatik/model/RailwayNetwork.java
+++ b/src/edu/kit/informatik/model/RailwayNetwork.java
@@ -27,16 +27,17 @@ public class RailwayNetwork {
      * Add a new track to the rail network.
      * @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 otherwise
+     * @return the positive identifier of the new track if successful, -1 if none available
+     * @throws InvalidInputException if the user provides incorrect input
      */
-    public int addTrack(final Vector2D start, final Vector2D end) {
+    public int addTrack(final Vector2D start, final Vector2D end) throws InvalidInputException {
         if (start.distanceTo(end) == 0) {
-            return -1;
+            throw new InvalidInputException("track has length zero");
         }
         long startPossibleConnections = rails.values().stream().filter((rail) -> rail.canConnectTo(start)).count();
         long endPossibleConnections = rails.values().stream().filter((rail) -> rail.canConnectTo(end)).count();
         if (startPossibleConnections == 2 || endPossibleConnections == 2) {
-            return -1; // TODO better error msg?
+            throw new InvalidInputException("track would connect to two other rails");
         }
         if (rails.isEmpty()) {
             Track newTrack = new Track(start, end, 1);
@@ -54,7 +55,7 @@ public class RailwayNetwork {
                     return newTrack.getIdentifier();
                 }
             }
-            return -1;
+            throw new InvalidInputException("track is not connected to other tracks");
         }
     }
 
@@ -104,13 +105,6 @@ public class RailwayNetwork {
     public boolean removeRail(final int id) {
         if (rails.size() == 0) {
             return false;
-        } else if (rails.size() == 1) {
-            if (rails.get(id) != null) {
-                rails.clear();
-                return true;
-            } else {
-                return false;
-            }
         }
         Rail toRemove = rails.get(id);
         if (toRemove == null) {
@@ -121,7 +115,7 @@ public class RailwayNetwork {
         // locate one other rail: TODO use rail.connectedrails
         Rail otherRail = null;
         for (Rail anotherRail : rails.values()) {
-            if (anotherRail.getIdentifier() != id && toRemove.canConnectToRail(anotherRail)) {
+            if (anotherRail.getIdentifier() != id && anotherRail.canConnectToRail(toRemove)) {
                 otherRail = anotherRail;
                 break;
             }
diff --git a/src/edu/kit/informatik/model/RollingStock.java b/src/edu/kit/informatik/model/RollingStock.java
index 8de7a6f..a3447ed 100644
--- a/src/edu/kit/informatik/model/RollingStock.java
+++ b/src/edu/kit/informatik/model/RollingStock.java
@@ -1,5 +1,7 @@
 package edu.kit.informatik.model;
 
+import edu.kit.informatik.ui.InvalidInputException;
+
 /**
  * A rolling stock. Is usually an engine, train set or coach.
  *
@@ -10,17 +12,28 @@ public abstract class RollingStock {
     /**
      * Length of this rolling stock.
      */
-    private int length;
+    private final int length;
     /**
      * Whether this rolling stock has a front coupling.
      */
-    private boolean couplingFront;
+    private final boolean couplingFront;
     /**
      * Whether this rolling stack has a back coupling.
      */
-    private boolean couplingBack;
+    private final boolean couplingBack;
 
-    protected RollingStock(final int length, final boolean couplingFront, final boolean couplingBack) {
+    /**
+     * Initialize a rolling stock.
+     * @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 (zero-sized coach)
+     */
+    protected RollingStock(final int length, final boolean couplingFront, final boolean couplingBack)
+            throws InvalidInputException {
+        if (length < 1) {
+            throw new InvalidInputException("rolling stock length has to be positive");
+        }
         this.length = length;
         this.couplingFront = couplingFront;
         this.couplingBack = couplingBack;
diff --git a/src/edu/kit/informatik/model/SteamEngine.java b/src/edu/kit/informatik/model/SteamEngine.java
index d426261..1aac074 100644
--- a/src/edu/kit/informatik/model/SteamEngine.java
+++ b/src/edu/kit/informatik/model/SteamEngine.java
@@ -1,5 +1,7 @@
 package edu.kit.informatik.model;
 
+import edu.kit.informatik.ui.InvalidInputException;
+
 /**
  * Steam engine.
  *
@@ -26,9 +28,10 @@ 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)
      */
     public SteamEngine(final String series, final String name, final int length,
-                       final boolean couplingFront, final boolean couplingBack) {
+                       final boolean couplingFront, final boolean couplingBack) throws InvalidInputException {
         super(series, name, length, couplingFront, couplingBack);
     }
 
diff --git a/src/edu/kit/informatik/model/Train.java b/src/edu/kit/informatik/model/Train.java
index bc0fddf..ad7ed1e 100644
--- a/src/edu/kit/informatik/model/Train.java
+++ b/src/edu/kit/informatik/model/Train.java
@@ -208,8 +208,9 @@ public final class Train {
         RollingStock last = rollingStocks.get(rollingStocks.size() - 1);
         // the first or last rolling stock HAVE TO BE an engine OR a train-set!
         // therefore, no other rolling stock types should be allowed at all.
+        // TODO: consider using first.canBeAtFront() ???
         return (first instanceof Engine || first instanceof TrainSet)
-                || (last instanceof Engine || last instanceof TrainSet);
+                || last instanceof Engine;
     }
 
     /**
@@ -248,11 +249,7 @@ public final class Train {
      * @return the rear direction of this train
      */
     public Vector2D getRearDirection() {
-        if (position.size() == 1) {
-            return direction.negated();
-        } else {
-            return position.getLast().subtract(position.get(position.size() - 2)); // TODO
-        }
+        return position.getLast().subtract(position.get(position.size() - 2)); // TODO: consider longer trains
     }
 
     /**
@@ -319,10 +316,7 @@ public final class Train {
             // we evidently just moved into another rail
             Rail[] nextTouchingRails = railNetwork.findTouchingRails(nextPosition);
             Rail[] alreadyTouchingRails = railNetwork.findTouchingRails(secondToLastPosition);
-            if (alreadyTouchingRails.length == 0) {
-                // we evidently just derailed, be we should still crash with trains entering our last rail
-                assert !occupiedRails.isEmpty();
-            } else if (nextTouchingRails[0] == alreadyTouchingRails[0]) {
+            if (nextTouchingRails[0] == alreadyTouchingRails[0]) {
                 occupiedRails.add(nextTouchingRails[0]);
             } else if (nextTouchingRails.length == 2) {
                 if (nextTouchingRails[1] == alreadyTouchingRails[0]) {
diff --git a/src/edu/kit/informatik/model/TrainSet.java b/src/edu/kit/informatik/model/TrainSet.java
index 4ffa9c6..cfafd6e 100644
--- a/src/edu/kit/informatik/model/TrainSet.java
+++ b/src/edu/kit/informatik/model/TrainSet.java
@@ -1,5 +1,7 @@
 package edu.kit.informatik.model;
 
+import edu.kit.informatik.ui.InvalidInputException;
+
 /**
  * Train set.
  *
@@ -37,9 +39,10 @@ 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)
      */
     public TrainSet(final String series, final String name, final int length,
-                    final boolean couplingFront, final boolean couplingBack) {
+                    final boolean couplingFront, final boolean couplingBack) throws InvalidInputException {
         super(length, couplingFront, couplingBack);
         this.name = name;
         this.series = series;
diff --git a/src/edu/kit/informatik/ui/command/AddTrack.java b/src/edu/kit/informatik/ui/command/AddTrack.java
index 0fc1cf5..243bf7a 100644
--- a/src/edu/kit/informatik/ui/command/AddTrack.java
+++ b/src/edu/kit/informatik/ui/command/AddTrack.java
@@ -3,6 +3,7 @@ package edu.kit.informatik.ui.command;
 import edu.kit.informatik.model.ModelRailwaySimulation;
 import edu.kit.informatik.model.Vector2D;
 import edu.kit.informatik.Terminal;
+import edu.kit.informatik.ui.InvalidInputException;
 
 /**
  * Command used to add a track to the rail network.
@@ -32,14 +33,10 @@ public class AddTrack extends Command {
     }
 
     @Override
-    public void apply(final ModelRailwaySimulation simulation) {
-        if (start.equals(end)) {
-            Terminal.printError("track has length 0");
-            return;
-        }
+    public void apply(final ModelRailwaySimulation simulation) throws InvalidInputException {
         int id = simulation.addTrack(start, end);
         if (id == -1) {
-            Terminal.printError("track is not connected to other tracks");
+            Terminal.printError("id space exhausted");
         } else {
             Terminal.printLine(id);
         }
diff --git a/src/edu/kit/informatik/ui/command/CommandFactory.java b/src/edu/kit/informatik/ui/command/CommandFactory.java
index e2af0c9..fb0ed1f 100644
--- a/src/edu/kit/informatik/ui/command/CommandFactory.java
+++ b/src/edu/kit/informatik/ui/command/CommandFactory.java
@@ -117,9 +117,6 @@ public class CommandFactory {
             }
             String name = matcher.group(3);
             int length = Integer.parseInt(matcher.group(4));
-            if (length < 1) {
-                throw new InvalidInputException("engine has to be positive length");
-            }
             boolean couplingFront = Boolean.parseBoolean(matcher.group(5));
             boolean couplingBack = Boolean.parseBoolean(matcher.group(6));
             return new CreateEngine(type, series, name, length, couplingFront, couplingBack);
diff --git a/src/edu/kit/informatik/ui/command/CreateCoach.java b/src/edu/kit/informatik/ui/command/CreateCoach.java
index 13cf393..d4bcc26 100644
--- a/src/edu/kit/informatik/ui/command/CreateCoach.java
+++ b/src/edu/kit/informatik/ui/command/CreateCoach.java
@@ -3,6 +3,7 @@ package edu.kit.informatik.ui.command;
 import edu.kit.informatik.ui.CoachType;
 import edu.kit.informatik.model.ModelRailwaySimulation;
 import edu.kit.informatik.Terminal;
+import edu.kit.informatik.ui.InvalidInputException;
 
 /**
  * Command used to create a single coach.
@@ -47,10 +48,10 @@ public class CreateCoach extends Command {
     }
 
     @Override
-    public void apply(final ModelRailwaySimulation simulation) {
+    public void apply(final ModelRailwaySimulation simulation) throws InvalidInputException {
         int id = simulation.createCoach(type, length, couplingFront, couplingBack);
         if (id == -1) {
-            Terminal.printError("could not add coach");
+            Terminal.printError("id space exhausted");
         } else {
             Terminal.printLine(id);
         }
diff --git a/testcoverage_input.txt b/testcoverage_input.txt
index e4a12eb..c1a8c83 100644
--- a/testcoverage_input.txt
+++ b/testcoverage_input.txt
@@ -38,6 +38,7 @@ create train-set T2 Epsilon 1 false false
 create train-set T2 Gamma 1 false false
 create train-set T2 Lambda 1 true true
 add train 3 T2-Lambda
+show train 3
 add train 5 T2-Epsilon
 list trains
 create coach passenger 1 true true
@@ -103,4 +104,46 @@ put train on my head
 put train 1 at (1,0) in direction 42,42
 add track to canada
 please just do as I say >:(
-step all over my legos, you dumb program
\ No newline at end of file
+step all over my legos, you dumb program
+delete track 5
+delete track 3
+delete track 2
+delete track 1
+delete track 4
+add switch (0,0) -> (-10,0),(0,10)
+add track (0,-10) -> (0,0)
+add track (-20,0) -> (-10,0)
+add track (0,20) -> (0,10)
+add track (0,30) -> (0,20)
+set switch 1 position (20,20)
+set switch 1 position (0,10)
+set switch 1 position (-10,0)
+put train 5 at (-5,0) in direction -1,0
+step 36
+delete track 5
+delete track 2
+delete track 3
+delete track 6
+delete track 4
+delete track 6
+delete track 1
+add track (0,0) -> (1,0)
+add track (1,0) -> (2,0)
+add track (2,0) -> (3,0)
+put train 5 at (1,0) in direction 1,0
+step 3
+add track (0,0) -> (0,0)
+add track (1,1) -> (1,0)
+add track (1,0) -> (1,1)
+create train-set T4 Einstein 1 false true
+create train-set T4 Newton 1 true false
+add train 7 T4-Einstein
+add train 7 T4-Newton
+create engine diesel T5 Hartnick 1 true false
+add train 6 T5-Hartnick
+put train 6 at (2,0) in direction 1,0
+step 2
+delete train 6
+add train 6 T5-Hartnick
+put train 6 at (0,0) in direction -1,0
+step 1
\ No newline at end of file
diff --git a/testcoverage_output.txt b/testcoverage_output.txt
index 8d8a043..de2cbec 100644
--- a/testcoverage_output.txt
+++ b/testcoverage_output.txt
@@ -31,7 +31,7 @@ OK
 OK
 1
 OK
-Error, engine has to be positive length
+Error, rolling stock length has to be positive
 T2-Gamma
 diesel engine T2-Gamma added to train 2
 OK
@@ -45,6 +45,14 @@ Error, identifier already used
 Error, identifier already used
 T2-Lambda
 train-set T2-Lambda added to train 3
+         ++         
+         ||         
+_________||_________
+|  ___ ___ ___ ___ |
+|  |_| |_| |_| |_| |
+|__________________|
+|__________________|
+   (O)        (O)   
 Error, new train identifier must be next free identifier
 1 T2-Phi T2-Rho T2-Omega W1 W2 W3
 2 T2-Gamma
@@ -121,3 +129,45 @@ Error, invalid train direction
 Error, invalid add track argument syntax
 Error, unknown command
 Error, invalid step argument
+OK
+OK
+OK
+OK
+OK
+1
+2
+3
+4
+5
+Error, could not set switch
+OK
+OK
+OK
+Crash of train 5
+OK
+OK
+OK
+Error, could not delete rail segment
+OK
+Error, could not delete rail segment
+OK
+1
+2
+3
+OK
+Crash of train 5
+Error, track has length zero
+Error, track would connect to two other rails
+Error, track would connect to two other rails
+T4-Einstein
+T4-Newton
+train-set T4-Einstein added to train 7
+train-set T4-Newton added to train 7
+T5-Hartnick
+diesel engine T5-Hartnick added to train 6
+OK
+Crash of train 6
+OK
+diesel engine T5-Hartnick added to train 6
+OK
+Crash of train 6