diff --git a/example2output.txt b/example2output.txt
index bc3a94a..c6646ee 100644
--- a/example2output.txt
+++ b/example2output.txt
@@ -11,10 +11,10 @@ Reihe1-Name1
 Reihe2-Name2
 Reihe3-Name3
 train-set Reihe2-Name2 added to train 1
-Error, could not modify train
+Error, could not add rolling stock to train
 diesel engine Reihe1-Name1 added to train 2
-Error, could not modify train
-Error, could not modify train
+Error, rolling stock already used
+Error, could not add rolling stock to train
 Reihe1-Name4
 electrical engine Reihe1-Name4 added to train 3
 Error, could not place train
diff --git a/fuzz10_output.txt b/fuzz10_output.txt
index 6534dd8..d6e37b0 100644
--- a/fuzz10_output.txt
+++ b/fuzz10_output.txt
@@ -15,7 +15,7 @@ OK
 passenger coach W1 added to train 1
 OK
 steam engine T3-Emma added to train 1
-Error, could not modify train
+Error, rolling stock not found
 403-145
 train-set 403-145 added to train 2
 OK
diff --git a/fuzz11_output.txt b/fuzz11_output.txt
index 6db33ea..6d151de 100644
--- a/fuzz11_output.txt
+++ b/fuzz11_output.txt
@@ -9,8 +9,8 @@ T3-Emma
 1
 2
 3
-Error, could not modify train
-Error, could not modify train
+Error, can not add rolling stock to placed train
+Error, can not add rolling stock to placed train
 Error, could not place train
 Crash of train 1
 OK
diff --git a/fuzz1_output.txt b/fuzz1_output.txt
index b2ccffd..429140f 100644
--- a/fuzz1_output.txt
+++ b/fuzz1_output.txt
@@ -11,7 +11,7 @@ diesel engine T3-Emma added to train 1
 3
 passenger coach W1 added to train 1
 passenger coach W2 added to train 1
-Error, could not modify train
+Error, could not add rolling stock to train
 Error, could not place train
 Error, rail tracks/switches not set up
 Error, rail tracks/switches not set up
diff --git a/src/edu/kit/informatik/MainTest.java b/src/edu/kit/informatik/MainTest.java
index 54771b1..9621be6 100644
--- a/src/edu/kit/informatik/MainTest.java
+++ b/src/edu/kit/informatik/MainTest.java
@@ -88,6 +88,11 @@ class MainTest {
         cmpInOut("fuzz11_input.txt", "fuzz11_output.txt");
     }
 
+    @Test
+    void testCoverage() throws IOException {
+        cmpInOut("testcoverage_input.txt", "testcoverage_output.txt");
+    }
+
     private void cmpInOut(String in, String out) throws IOException {
         System.setIn(new ByteArrayInputStream(readFile(in)));
         ByteArrayOutputStream output = new ByteArrayOutputStream();
diff --git a/src/edu/kit/informatik/model/Coach.java b/src/edu/kit/informatik/model/Coach.java
index b0498e8..977a1d0 100644
--- a/src/edu/kit/informatik/model/Coach.java
+++ b/src/edu/kit/informatik/model/Coach.java
@@ -75,14 +75,8 @@ public class Coach extends RollingStock {
     }
 
     @Override
-    public boolean canCoupleFrontTo(RollingStock rollingStock) {
-        // train-sets can ONLY connect to other matching train-sets, not to coaches.
-        return hasCouplingFront() && rollingStock.hasCouplingBack() && !(rollingStock instanceof TrainSet);
-    }
-
-    @Override
-    public boolean canCoupleToTrainSetSeries(String series) {
-        return false;
+    public boolean canCoupleTo(RollingStock rollingStock) {
+        return true;
     }
 
     /**
diff --git a/src/edu/kit/informatik/model/Engine.java b/src/edu/kit/informatik/model/Engine.java
index 8cdb6d7..0dd26e0 100644
--- a/src/edu/kit/informatik/model/Engine.java
+++ b/src/edu/kit/informatik/model/Engine.java
@@ -43,13 +43,7 @@ public abstract class Engine extends RollingStock {
     }
 
     @Override
-    public boolean canCoupleFrontTo(RollingStock rollingStock) {
-        // train-sets can ONLY connect to other matching train-sets, not to engines.
-        return hasCouplingFront() && rollingStock.hasCouplingBack() && !(rollingStock instanceof TrainSet);
-    }
-
-    @Override
-    public boolean canCoupleToTrainSetSeries(String series) {
-        return false;
+    public boolean canCoupleTo(RollingStock rollingStock) {
+        return true;
     }
 }
diff --git a/src/edu/kit/informatik/model/ModelRailwaySimulation.java b/src/edu/kit/informatik/model/ModelRailwaySimulation.java
index 4951c27..b089d52 100644
--- a/src/edu/kit/informatik/model/ModelRailwaySimulation.java
+++ b/src/edu/kit/informatik/model/ModelRailwaySimulation.java
@@ -101,22 +101,21 @@ public class ModelRailwaySimulation {
 
     /**
      * @param newEngine the engine to add to the simulation
-     * @return whether adding this engine was successful
+     * @throws InvalidInputException when the identifier is already in use
      */
-    public boolean createEngine(final Engine newEngine) {
+    public void createEngine(final Engine newEngine) throws InvalidInputException {
         String id = newEngine.getIdentifier();
         for (Engine engine : engines) {
             if (engine.getIdentifier().equals(id)) {
-                return false;
+                throw new InvalidInputException("identifier already used");
             }
         }
         for (TrainSet trainSet : trainSets) {
             if (trainSet.getIdentifier().equals(id)) {
-                return false;
+                throw new InvalidInputException("identifier already used");
             }
         }
         engines.add(newEngine);
-        return true;
     }
 
     /**
@@ -198,22 +197,21 @@ public class ModelRailwaySimulation {
     /**
      * Add a new train set to the simulation.
      * @param newTrainSet the train set to add
-     * @return true if the train set was successfully added, false otherwise
+     * @throws InvalidInputException if the identifier is already used
      */
-    public boolean createTrainSet(final TrainSet newTrainSet) {
+    public void createTrainSet(final TrainSet newTrainSet) throws InvalidInputException {
         String id = newTrainSet.getIdentifier();
         for (Engine engine : engines) {
             if (engine.getIdentifier().equals(id)) {
-                return false;
+                throw new InvalidInputException("identifier already used");
             }
         }
         for (TrainSet trainSet : trainSets) {
             if (trainSet.getIdentifier().equals(id)) {
-                return false;
+                throw new InvalidInputException("identifier already used");
             }
         }
         trainSets.add(newTrainSet);
-        return true;
     }
 
     /**
@@ -285,32 +283,32 @@ public class ModelRailwaySimulation {
      * Create a new train or add rolling stock to an existing train.
      * @param trainId identifier of the train
      * @param rollingStockId identifier of the rolling stock
-     * @return whether the operation was successful
+     * @throws InvalidInputException if input is incorrect
      */
-    public boolean addTrain(int trainId, String rollingStockId) {
+    public void addTrain(int trainId, String rollingStockId) throws InvalidInputException {
         RollingStock rollingStock = getRollingStock(rollingStockId);
         if (rollingStock == null) {
-            return false;
+            throw new InvalidInputException("rolling stock not found");
         }
         for (Train train : trains.values()) {
             if (train.contains(rollingStock)) {
-                return false;
+                throw new InvalidInputException("rolling stock already used");
             }
         }
         Train train = trains.get(trainId);
         if (train != null && train.isPlaced()) {
-            return false;
+            throw new InvalidInputException("can not add rolling stock to placed train");
         }
         if (train != null) {
-            return train.add(rollingStock);
+            train.add(rollingStock);
+            return;
         }
         int correctId = getNextTrainIdentifier();
         if (trainId != correctId) {
-            return false;
+            throw new InvalidInputException("new train identifier must be next free identifier");
         }
         Train newTrain = new Train(trainId, rollingStock);
         trains.put(trainId, newTrain);
-        return true;
     }
 
     /**
@@ -403,11 +401,8 @@ public class ModelRailwaySimulation {
      * @return list of collisions (never null, sometimes empty)
      */
     private ArrayList<HashSet<Train>> getStaticCollisions() {
-        if (trains.isEmpty()) {
-            return new ArrayList<>();
-        }
         ArrayList<HashSet<Train>> collisions = new ArrayList<>();
-        int maxId = trains.keySet().stream().max(Integer::compareTo).get();
+        int maxId = trains.keySet().stream().max(Integer::compareTo).orElse(0);
         train: for (int id1 = 1; id1 <= maxId; id1++) {
             Train train1 = trains.get(id1);
             if (train1 == null || !train1.isPlaced()) {
diff --git a/src/edu/kit/informatik/model/RailwayNetwork.java b/src/edu/kit/informatik/model/RailwayNetwork.java
index 1dafb5d..c68664b 100644
--- a/src/edu/kit/informatik/model/RailwayNetwork.java
+++ b/src/edu/kit/informatik/model/RailwayNetwork.java
@@ -211,7 +211,7 @@ public class RailwayNetwork {
             // at the end of a rail
             // either derail or move backwards
             Vector2D nextPosition = position.add(direction);
-            if (!touchingRails[0].contains(nextPosition)) {
+            if (!touchingRails[0].contains(nextPosition) && !touchingRails[0].connectsTo(nextPosition)) {
                 return null;
             } else {
                 return nextPosition;
diff --git a/src/edu/kit/informatik/model/RollingStock.java b/src/edu/kit/informatik/model/RollingStock.java
index 7963532..8de7a6f 100644
--- a/src/edu/kit/informatik/model/RollingStock.java
+++ b/src/edu/kit/informatik/model/RollingStock.java
@@ -54,15 +54,9 @@ public abstract class RollingStock {
 
     /**
      * @param rollingStock other rolling stock
-     * @return whether this rolling stock can couple to the back of the other rolling stock
+     * @return whether this rolling stock can couple to the other rolling stock
      */
-    public abstract boolean canCoupleFrontTo(RollingStock rollingStock);
-
-    /**
-     * @param series series/class of train set
-     * @return whether this rolling stock can couple to train sets of that series
-     */
-    public abstract boolean canCoupleToTrainSetSeries(String series);
+    public abstract boolean canCoupleTo(RollingStock rollingStock);
 
     /**
      * @return ASCII art representation of this rolling stock
diff --git a/src/edu/kit/informatik/model/Train.java b/src/edu/kit/informatik/model/Train.java
index 9989086..bc0fddf 100644
--- a/src/edu/kit/informatik/model/Train.java
+++ b/src/edu/kit/informatik/model/Train.java
@@ -65,14 +65,16 @@ public final class Train {
     /**
      * Add a rolling stock to this train.
      * @param rollingStock the rolling stack to add
-     * @return whether the modification was successful
+     * @throws InvalidInputException if the rolling stock could not be added to the train
      */
-    public boolean add(RollingStock rollingStock) {
-        if (rollingStock.canCoupleFrontTo(rollingStocks.get(rollingStocks.size() - 1))) {
+    public void add(RollingStock rollingStock) throws InvalidInputException {
+        RollingStock last = rollingStocks.get(rollingStocks.size() - 1);
+        if (rollingStock.hasCouplingFront() && last.hasCouplingBack()
+                && rollingStock.canCoupleTo(last) && last.canCoupleTo(rollingStock)) {
             rollingStocks.add(rollingStock);
-            return true;
+        } else {
+            throw new InvalidInputException("could not add rolling stock to train");
         }
-        return false;
     }
 
     @Override
@@ -95,24 +97,23 @@ public final class Train {
             for (StringBuilder line : lines) {
                 line.append(' ');
             }
+            int currentLength = lines.stream().mapToInt(StringBuilder::length).max().orElse(0);
             while (lines.size() < text.length) {
                 StringBuilder line = new StringBuilder();
                 if (!lines.isEmpty()) {
-                    for (int i = 0; i < lines.get(0).length(); i++) {
+                    for (int i = 0; i < currentLength; i++) {
                         line.append(' ');
                     }
                 }
-                lines.add(line);
+                lines.add(0, line);
             }
             for (int i = 0; i < text.length; i++) {
                 lines.get(lines.size() - 1 - i).append(text[text.length - 1 - i]);
             }
-            int finalLength = lines.get(lines.size() - 1).length();
+            int finalLength = lines.stream().mapToInt(StringBuilder::length).max().getAsInt();
             for (StringBuilder line : lines) {
-                if (line.length() < finalLength) {
-                    for (int i = 0; i < finalLength - line.length(); i++) {
-                        line.append(' ');
-                    }
+                while (line.length() < finalLength) {
+                    line.append(' ');
                 }
             }
         }
@@ -144,7 +145,7 @@ public final class Train {
         Vector2D direction = rawDirection.normalized();
         long length = getLength();
         if (length > Integer.MAX_VALUE) {
-            // we can not create a position list this long! TODO: await forum answer
+            // TODO: implement this case
             throw new InvalidInputException("train length is bigger than 32-bit integer!");
         }
 
@@ -174,7 +175,7 @@ public final class Train {
             } else if (i > 0) {
                 Rail[] touchingRails = railNetwork.findTouchingRails(point);
                 for (Rail rail : touchingRails) {
-                    if (positions.stream().anyMatch(rail::connectsTo)) {
+                    if (positions.stream().filter(rail::connectsTo).count() == 2) {
                         // ONLY add this rail if we actually occupy it fully
                         // note that this edge case only happens with rails of length one:
                         // otherwise at least one position will be contained in the rail (see above)
diff --git a/src/edu/kit/informatik/model/TrainSet.java b/src/edu/kit/informatik/model/TrainSet.java
index e6e1d83..4ffa9c6 100644
--- a/src/edu/kit/informatik/model/TrainSet.java
+++ b/src/edu/kit/informatik/model/TrainSet.java
@@ -56,13 +56,8 @@ public class TrainSet extends RollingStock {
     }
 
     @Override
-    public boolean canCoupleFrontTo(RollingStock rollingStock) {
-        return hasCouplingFront() && rollingStock.hasCouplingBack() && rollingStock.canCoupleToTrainSetSeries(series);
-    }
-
-    @Override
-    public boolean canCoupleToTrainSetSeries(String series) {
-        return this.series.equals(series);
+    public boolean canCoupleTo(RollingStock rollingStock) {
+        return rollingStock.getClass().equals(this.getClass()) && ((TrainSet) rollingStock).series.equals(this.series);
     }
 
     @Override
diff --git a/src/edu/kit/informatik/ui/command/AddTrain.java b/src/edu/kit/informatik/ui/command/AddTrain.java
index d4ace01..1541004 100644
--- a/src/edu/kit/informatik/ui/command/AddTrain.java
+++ b/src/edu/kit/informatik/ui/command/AddTrain.java
@@ -3,6 +3,7 @@ package edu.kit.informatik.ui.command;
 import edu.kit.informatik.model.ModelRailwaySimulation;
 import edu.kit.informatik.model.RollingStock;
 import edu.kit.informatik.Terminal;
+import edu.kit.informatik.ui.InvalidInputException;
 
 /**
  * Command used to construct a new train or modify an existing train.
@@ -31,13 +32,10 @@ public class AddTrain extends Command {
     }
 
     @Override
-    public void apply(final ModelRailwaySimulation simulation) {
-        if (simulation.addTrain(trainId, rollingStockId)) {
-            RollingStock rollingStock = simulation.getRollingStock(rollingStockId);
-            Terminal.printLine(String.format("%s %s added to train %d",
-                    rollingStock.description(), rollingStock.getIdentifier(), trainId));
-        } else {
-            Terminal.printError("could not modify train");
-        }
+    public void apply(final ModelRailwaySimulation simulation) throws InvalidInputException {
+        simulation.addTrain(trainId, rollingStockId);
+        RollingStock rollingStock = simulation.getRollingStock(rollingStockId);
+        Terminal.printLine(String.format("%s %s added to train %d",
+                rollingStock.description(), rollingStock.getIdentifier(), trainId));
     }
 }
diff --git a/src/edu/kit/informatik/ui/command/CreateEngine.java b/src/edu/kit/informatik/ui/command/CreateEngine.java
index 7dc9d9c..fe15dc6 100644
--- a/src/edu/kit/informatik/ui/command/CreateEngine.java
+++ b/src/edu/kit/informatik/ui/command/CreateEngine.java
@@ -7,6 +7,7 @@ import edu.kit.informatik.model.Engine;
 import edu.kit.informatik.model.ModelRailwaySimulation;
 import edu.kit.informatik.model.SteamEngine;
 import edu.kit.informatik.ui.EngineType;
+import edu.kit.informatik.ui.InvalidInputException;
 
 /**
  * Command used to create a single engine.
@@ -63,7 +64,7 @@ public class CreateEngine extends Command {
     }
 
     @Override
-    public void apply(final ModelRailwaySimulation simulation) {
+    public void apply(final ModelRailwaySimulation simulation) throws InvalidInputException {
         Engine engine;
         switch (type) {
             case ELECTRICAL:
@@ -78,10 +79,7 @@ public class CreateEngine extends Command {
             default:
                 throw new IllegalStateException("engine type is null!");
         }
-        if (simulation.createEngine(engine)) {
-            Terminal.printLine(engine.getIdentifier());
-        } else {
-            Terminal.printLine("could not create engine");
-        }
+        simulation.createEngine(engine);
+        Terminal.printLine(engine.getIdentifier());
     }
 }
diff --git a/src/edu/kit/informatik/ui/command/CreateTrainSet.java b/src/edu/kit/informatik/ui/command/CreateTrainSet.java
index 4702e0b..94aa3df 100644
--- a/src/edu/kit/informatik/ui/command/CreateTrainSet.java
+++ b/src/edu/kit/informatik/ui/command/CreateTrainSet.java
@@ -3,6 +3,7 @@ package edu.kit.informatik.ui.command;
 import edu.kit.informatik.model.ModelRailwaySimulation;
 import edu.kit.informatik.Terminal;
 import edu.kit.informatik.model.TrainSet;
+import edu.kit.informatik.ui.InvalidInputException;
 
 /**
  * Command used to add a new train set.
@@ -50,12 +51,9 @@ public class CreateTrainSet extends Command {
     }
 
     @Override
-    public void apply(final ModelRailwaySimulation simulation) {
+    public void apply(final ModelRailwaySimulation simulation) throws InvalidInputException {
         TrainSet trainSet = new TrainSet(series, name, length, couplingFront, couplingBack);
-        if (simulation.createTrainSet(trainSet)) {
-            Terminal.printLine(trainSet.getIdentifier());
-        } else {
-            Terminal.printError("could not add train-set");
-        }
+        simulation.createTrainSet(trainSet);
+        Terminal.printLine(trainSet.getIdentifier());
     }
 }
diff --git a/testcoverage_input.txt b/testcoverage_input.txt
new file mode 100644
index 0000000..63bc8fd
--- /dev/null
+++ b/testcoverage_input.txt
@@ -0,0 +1,63 @@
+list coaches
+list trains
+list train-sets
+list engines
+create engine diesel T2 Phi 1 true true
+create engine steam T2 Rho 3 true true
+create engine electrical T2 Omega 2 true true
+add train 1 T2-Phi
+add train 1 T2-Rho
+add train 1 T2-Omega
+create coach passenger 1 true true
+create coach freight 1 true true
+create coach special 1 true true
+add train 1 W1
+add train 1 W2
+add train 1 W3
+show train +01
+show train 00042
+put train 42 at (10,0) in direction 1,0
+create coach passenger 1 true true
+add train 2 W4
+put train 2 at (0,0) in direction -1,0
+delete train 2
+delete rolling stock W4
+add switch (0,0) -> (1,0),(0,1)
+set switch 1 position (1,0)
+create engine diesel T2 Delta 0 true true
+create engine diesel T2 Gamma 1 true true
+add train 2 T2-Gamma
+put train 2 at (0,0) in direction -1,0
+add track (1,0) -> (10,0)
+delete track 2
+step 1
+create engine diesel T2 Gamma 10 false false
+create train-set T2 Epsilon 1 false false
+create engine steam T2 Epsilon 1 false false
+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
+add train 5 T2-Epsilon
+list trains
+create coach passenger 1 true true
+create coach passenger 1 true true
+delete rolling stock W4
+create coach passenger 1 true true
+delete rolling stock W5
+list coaches
+list train-sets
+list engines
+delete train 1
+add train 1 T2-Omega
+add train 4 W1
+add train 5 T2-Phi
+add train 6 W2
+delete train 2
+delete train 3
+delete train 4
+add train 2 T2-Rho
+add track (1,0) -> (10,0)
+put train 1 at (7,0) in direction -1,0
+put train 5 at (0,0) in direction -1,0
+step 8
\ No newline at end of file
diff --git a/testcoverage_output.txt b/testcoverage_output.txt
new file mode 100644
index 0000000..8378a14
--- /dev/null
+++ b/testcoverage_output.txt
@@ -0,0 +1,80 @@
+No coach exists
+No train exists
+No train-set exists
+No engine exists
+T2-Phi
+T2-Rho
+T2-Omega
+diesel engine T2-Phi added to train 1
+steam engine T2-Rho added to train 1
+electrical engine T2-Omega added to train 1
+1
+2
+3
+passenger coach W1 added to train 1
+freight coach W2 added to train 1
+special coach W3 added to train 1
+                                                           ___                                                                   
+                                                             \                                                               ____
+  _____________|____        ++      +------   _______________/__    ____________________                      /--------------|  |
+ /_| ____________ |_\       ||      |+-+ |   /_| ____________ |_\   |  ___ ___ ___ ___ | |                  | \--------------|  |
+/   |____________|   \    /---------|| | |  /   |____________|   \  |  |_| |_| |_| |_| | |                  |   | |          |  |
+\                    /   + ========  +-+ |  \                    /  |__________________| |                  |  _|_|__________|  |
+ \__________________/   _|--/~\------/~\-+   \__________________/   |__________________| |__________________| |_________________|
+  (O)(O)      (O)(O)   //// \_/      \_/      (O)(O)      (O)(O)       (O)        (O)       (O)        (O)       (O)       (O)   
+Error, no such train
+Error, could not place train
+4
+passenger coach W4 added to train 2
+Error, could not place train
+OK
+OK
+1
+OK
+Error, engine has to be positive length
+T2-Gamma
+diesel engine T2-Gamma added to train 2
+OK
+2
+OK
+Crash of train 2
+Error, identifier already used
+T2-Epsilon
+Error, identifier already used
+Error, identifier already used
+Error, identifier already used
+T2-Lambda
+train-set T2-Lambda added to train 3
+Error, new train identifier must be next free identifier
+1 T2-Phi T2-Rho T2-Omega W1 W2 W3
+2 T2-Gamma
+3 T2-Lambda
+4
+5
+OK
+4
+OK
+1 1 p 1 true true
+2 1 f 1 true true
+3 1 s 1 true true
+4 none p 1 true true
+none T2 Epsilon 1 false false
+3 T2 Lambda 1 true true
+2 d T2 Gamma 1 true true
+1 e T2 Omega 2 true true
+1 d T2 Phi 1 true true
+1 s T2 Rho 3 true true
+OK
+electrical engine T2-Omega added to train 1
+passenger coach W1 added to train 4
+diesel engine T2-Phi added to train 5
+freight coach W2 added to train 6
+OK
+OK
+OK
+steam engine T2-Rho added to train 2
+2
+OK
+OK
+Crash of train 1
+Crash of train 5