diff --git a/app/src/main/java/de/hems/trafficsim/MainActivity.java b/app/src/main/java/de/hems/trafficsim/MainActivity.java
index f185b30..e2581c5 100644
--- a/app/src/main/java/de/hems/trafficsim/MainActivity.java
+++ b/app/src/main/java/de/hems/trafficsim/MainActivity.java
@@ -5,6 +5,7 @@ import androidx.constraintlayout.widget.ConstraintLayout;
 
 import android.os.Bundle;
 import android.view.View;
+import android.widget.Button;
 import android.widget.TextView;
 
 import java.util.Observable;
@@ -14,12 +15,13 @@ public class MainActivity extends AppCompatActivity implements Observer {
 
     protected Track track;
     protected TrackView trackView;
+    protected Worker worker;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
-        this.track = new Track(20, 50);
+        this.track = new Track(25, 100);
         this.trackView = new TrackView(this, this.track);
         this.track.addObserver(this);
         ConstraintLayout layout = (ConstraintLayout) findViewById(R.id.constr_layout);
@@ -28,23 +30,59 @@ public class MainActivity extends AppCompatActivity implements Observer {
 
     @Override
     public void update(Observable observable, Object o) {
-        String s = "";
-        for (Vehicle v: this.track.getVehicles()){
-            s+= "Vehicle " + v.id + "   |   "
-                    + "Pos = " + v.getPosition() + "   |   "
-                    + "Vel = " + v.getCurVelocity()+ "   |   "
-                    + "\n";
-            ;
-        }
-        TextView view = (TextView) findViewById(R.id.debugTextView);
-        view.setText(s);
-        view.invalidate();
-        this.trackView.invalidate();
+        final Track trackRef = this.track;
+        final TrackView viewRef = this.trackView;
+        runOnUiThread(new Runnable() {
+            @Override
+            public void run() {
+                String s = "";
+                for (Vehicle v: trackRef.getVehicles()){
+                    s+= "Vehicle " + v.id + "   |   "
+                            + "Pos = " + v.getPosition() + "   |   "
+                            + "Vel = " + v.getCurVelocity()+ "   |   "
+                            + "\n";
+                    ;
+                }
+                TextView view = (TextView) findViewById(R.id.debugTextView);
+                view.setText(s);
+                view.invalidate();
+                viewRef.invalidate();
+            }
+        });
+
     }
 
-    public void onStepButtonClick (View view) {
+    public void onStepButtonClick(View view) {
         //for (int j = 0; j < 3000; j++) {
             this.track.timeElapse(50);
         //}
     }
+
+    public void onPlayButtonClick(View view) {
+        Button playButton = (Button) findViewById(R.id.playButton);
+        playButton.setEnabled(false);
+        Button stepButton = (Button) findViewById(R.id.stepButton);
+        stepButton.setEnabled(false);
+        Button stopButton = (Button) findViewById(R.id.stopButton);
+        stopButton.setEnabled(true);
+
+        this.worker = new Worker(track);
+        this.worker.start();
+    }
+
+    public void onStopButtonClick(View view) {
+        Button playButton = (Button) findViewById(R.id.playButton);
+        playButton.setEnabled(true);
+        Button stepButton = (Button) findViewById(R.id.stepButton);
+        stepButton.setEnabled(true);
+        Button stopButton = (Button) findViewById(R.id.stopButton);
+        stopButton.setEnabled(false);
+
+        this.worker.setStop(true);
+        try {
+            this.worker.join();
+        } catch (InterruptedException ex) {
+
+        }
+    }
 }
\ No newline at end of file
diff --git a/app/src/main/java/de/hems/trafficsim/Track.java b/app/src/main/java/de/hems/trafficsim/Track.java
index 3b16013..db6a655 100644
--- a/app/src/main/java/de/hems/trafficsim/Track.java
+++ b/app/src/main/java/de/hems/trafficsim/Track.java
@@ -17,14 +17,15 @@ public class Track extends Observable {
     }
 
     public Track(int numberVehicles, float trackLength) {
-        this.vehicles = createVehiclesList(numberVehicles);
         this.trackLength = trackLength;
+        this.vehicles = createVehiclesList(numberVehicles);
+
     }
 
     protected List<Vehicle> createVehiclesList(int numberVehicles){
         List<Vehicle> result = new ArrayList<>();
         for(int i=0;i<numberVehicles;i++){
-            Vehicle vehicle = new Vehicle(i, i, 5, 0.2f);
+            Vehicle vehicle = new Vehicle(i, i, 5, 0.2f, this.trackLength);
             result.add(vehicle);
         }
 
diff --git a/app/src/main/java/de/hems/trafficsim/Vehicle.java b/app/src/main/java/de/hems/trafficsim/Vehicle.java
index e80c750..e6fbb0b 100644
--- a/app/src/main/java/de/hems/trafficsim/Vehicle.java
+++ b/app/src/main/java/de/hems/trafficsim/Vehicle.java
@@ -8,14 +8,16 @@ public class Vehicle {
     protected float curVelocity;
     protected float maxVelocity;
     protected float brakeProp;
+    protected float trackLength;
 
 
-    public Vehicle(int id, int position, float maxVelocity, float brakeProp) {
+    public Vehicle(int id, int position, float maxVelocity, float brakeProp, float trackLength) {
         this.id = id;
         this.position = position;
         this.maxVelocity = maxVelocity;
         this.brakeProp = brakeProp;
         this.curVelocity = 0;
+        this.trackLength = trackLength;
 
     }
 
@@ -49,7 +51,7 @@ public class Vehicle {
     }
 
     public void timeElapse(float timeStep) {
-        position = (position + curVelocity) % 50;
+        position = (position + curVelocity) % this.trackLength;
     }
 
 }
diff --git a/app/src/main/java/de/hems/trafficsim/Worker.java b/app/src/main/java/de/hems/trafficsim/Worker.java
new file mode 100644
index 0000000..862f60f
--- /dev/null
+++ b/app/src/main/java/de/hems/trafficsim/Worker.java
@@ -0,0 +1,22 @@
+package de.hems.trafficsim;
+
+public class Worker extends Thread {
+    protected Track track;
+    protected boolean stop;
+    public Worker(Track track) {
+        super();
+        this.track = track;
+        this.stop = false;
+    }
+
+    void setStop(boolean stop) {
+        this.stop = stop;
+    }
+
+    @Override
+    public void run() {
+        while (!stop) {
+            this.track.timeElapse(50);
+        }
+    }
+}
diff --git a/app/src/main/res/layout/activity_main.xml b/app/src/main/res/layout/activity_main.xml
index 02df76f..4cb5ebd 100644
--- a/app/src/main/res/layout/activity_main.xml
+++ b/app/src/main/res/layout/activity_main.xml
@@ -7,6 +7,19 @@
     android:layout_height="match_parent"
     tools:context=".MainActivity">
 
+    <Button
+        android:id="@+id/stopButton"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginBottom="16dp"
+        android:enabled="false"
+        android:onClick="onStopButtonClick"
+        android:text="Stop"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintHorizontal_bias="0.95"
+        app:layout_constraintStart_toStartOf="parent" />
+
     <TextView
         android:id="@+id/debugTextView"
         android:layout_width="wrap_content"
@@ -23,9 +36,21 @@
         android:layout_height="wrap_content"
         android:layout_marginBottom="16dp"
         android:onClick="onStepButtonClick"
-        android:text="Button"
+        android:text="Step"
         app:layout_constraintBottom_toBottomOf="parent"
         app:layout_constraintEnd_toEndOf="parent"
         app:layout_constraintHorizontal_bias="0.5"
         app:layout_constraintStart_toStartOf="parent" />
+
+    <Button
+        android:id="@+id/playButton"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginBottom="16dp"
+        android:onClick="onPlayButtonClick"
+        android:text="Play"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintHorizontal_bias="0.049"
+        app:layout_constraintStart_toStartOf="parent" />
 </androidx.constraintlayout.widget.ConstraintLayout>
\ No newline at end of file