diff --git a/World.java b/World.java
index 31382b6..4c7411c 100644
--- a/World.java
+++ b/World.java
@@ -4,9 +4,11 @@ import java.util.Random;
 class World implements Drawable
 {
     private static final int DISTANCE = 250;
+    private static final int START_SPEED = 150;
+    private static final int ACCELERATION = 2;
+
     private final ArrayList<Rectangle> _obstacles;
-    private double _speed = 150;
-    private double _acc = 2;
+    private double _speed;
     private final Random _random;
 
     public World(GameScreen game)
@@ -21,6 +23,7 @@ class World implements Drawable
     {
         _obstacles.clear();
         createObstacle(TurtleWelt.WIDTH);
+        _speed = START_SPEED;
     }
 
     private void createObstacle(int x)
@@ -58,7 +61,7 @@ class World implements Drawable
         }
 
         // Increase speed according to acceleration
-        _speed += _acc * elapsed * 1e-3;
+        _speed += ACCELERATION * elapsed * 1e-3;
     }
 
     public boolean checkCollision(Rectangle r)