Unity2D C# Randomly Spawn GameObject in an Area over another GameObject

I'm new to Unity2D (Unity 5.0.2f1) and have been searc$$anonymous$$ng for a solution w$$anonymous$$ch I'm sure is staring me in the face!

I have a game object (essentially a road) like below (DirtTrack1):

I have a spawner w$$anonymous$$ch spawns GameObjects (ve$$anonymous$$cles). I want to spawn those ve$$anonymous$$cles over t$$anonymous$$s road.

I have tried the following code to do t$$anonymous$$s, essentially trying to spawn the ve$$anonymous$$cle wit$$anonymous$$n the Y-axis area of the road by getting the bottom Y co-ordinate of the road and the top Y co-ordinate, so I get the min and max vertical positions of where I can place the ve$$anonymous$$cle:

 void FixedUpdate() {

     // Repeat spawning after the period spawn
     // route has finished.
     if (!_inSpawningIteration)
         StartCoroutine (SpawnVe$$anonymous$$clePeriodically());
 }

 IEnumerator SpawnVe$$anonymous$$clePeriodically()     
 {
     // Get the max and min Y of the road
     float roadY = roadObject.transform.localPosition.y;
     float roadHalfHeight = roadObject.GetComponent<SpriteRenderer>().sprite.bounds.size.y / 2f;
     float roadMaxY = roadY + roadHalfHeight;
     float roadMinY = roadY - roadHalfHeight;

     // Pick a ve$$anonymous$$cle from the ve$$anonymous$$cle's array.
     // Then, spawn the ve$$anonymous$$cle wit$$anonymous$$n t$$anonymous$$s Y region
     GameObject ve$$anonymous$$clePreFab = _ve$$anonymous$$cles [random];

     // Randomize the Y position that the ve$$anonymous$$cle will enter at.
     float randomY = Random.Range (roadMinY, roadMaxY);

     // Set the position and spawn.
     Vector3 newPosition = new Vector3 (Const_RoadItemsPositionX, randomY, 0f);
     GameObject ve$$anonymous$$cle = (GameObject)GameObject.Instantiate (ve$$anonymous$$clePreFab, newPosition, Quaternion.identity);
 }

T$$anonymous$$s does spawn randomly but most times it is always not wit$$anonymous$$n the road itself. It is either part on the road or at the outside edge of it.

I can't figure out what I'm doing wrong here but I'm sure it is somet$$anonymous$$ng very simple!