Movement on roads issue

So I'm trying to get a computer character to follow a road map. Basically it picks a random intersection to move towards, only re-adjusting if it wanders off the road by moving towards the closest road. I spent a few days trying to fix the original problem of it wandering off of the road randomly, but now I have another problem:

The character follows a loose pattern along the road, but doesn't save the closest road; instead it picks a random one far away. Also, the character still isn't moving towards the intersection that it says it's going after. I used a Debug.Log to print the point and it's setting it as just a vague (Object) instead of an actual point...here is the code I have so far:(One note, I excluded the variable initializations)

EDIT: Thanks to superluigi's advice, I started using navmesh...this is the new code in case anybody else needs it.

 #pragma strict
 
 var agent: NavMeshAgent;
 var target: GameObject;
 var moveSpeed : float = 6.0;
 var gravity : float = 10.0;//basic stuff
 var wayPointsAr: GameObject[] ;
 var MyIndex;
 var dist:float;
 
 function Awake()
 {
 agent=GetComponent(NavMeshAgent);
 wayPointsAr= GameObject.FindGameObjectsWithTag("waytag");//tags all waypoint objects
 MyIndex = Random.Range(0,(wayPointsAr.length - 1));
 target=wayPointsAr[MyIndex];
 Debug.Log(target.transform.position);
 }
 
 function Update() 
 {
 agent.SetDestination(target.transform.position);
 dist=Vector3.Distance(target.transform.position,transform.position);
 if (dist<50)
     {
     MyIndex = Random.Range(0,(wayPointsAr.length - 1));
     target=wayPointsAr[MyIndex];
     Debug.Log(target.transform.position);
     }
 }