How to add progress bar showing player movement from start to finish line in 3d game ?,

I have added progress bar w$$anonymous$$ch is working fine for straight path. but in curve path as shown in figure the progress bar starts moving backwards due to decrease in z position of car. I have added many check point to calculate the distance between them and added them. but issue with current position. how to manage current position of car and move the progress bar.

 public Transform LevelEndCheckpoint;
 public Slider ProgressSlider;
 private float totalDistance,current_position,playerPosition;
 // Use t$$anonymous$$s for initialization
 void OnEnable () {
     playerPosition = t$$anonymous$$s.transform.position.z;
     //totalDistance = LevelEndCheckpoint.transform.position.z -  playerPosition;
             for (int i = 0; i < p_Length; i++) {
         totalDistance += Vector3.Distance( AllPoints [i + 1].position , AllPoints [i].position);
     }
     ProgressSlider.maxValue = -totalDistance;
     ProgressSlider.minValue = -playerPosition;
 }
 void Update () {
     playerPosition = -t$$anonymous$$s.transform.position.z;
     ProgressSlider.value = playerPosition;
 }

![alt text][1] ![alt text][2] [1]: /storage/temp/121792-screenshot-10.png [2]: /storage/temp/121793-screenshot-11.jpg

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