How to restrict touch movement for android.

Questions & Answers
1

Hey, i am working on a 2D car racing game for android device. I have coded the touch movement for my car. But the problem is the car is going beyond the track. How can i restrict the car movement, i mean how can i code for my car to stay in the screen(Screen resulation is 480*800 and car sprites max position is 4.2 and min -4.2). Here r my C# car controller script.
using UnityEngine;
using System.Collections;

public class carController : MonoBehaviour {

public float carSpeed;


// Update is called once per frame
void Update () {

	if (Input.touchCount == 1) {
	
		Touch touch = Input.touches[0];
		if(touch.position.x < Screen.width/2){
			transform.position += Vector3.left * carSpeed * Time.deltaTime;

		}
		else if(touch.position.x > Screen.width/2){
			transform.position += Vector3.right * carSpeed * Time.deltaTime;

		}
	
	}
}

}

2

Use colliders to define the boundaries of the track

3

if(touch.position.x < Screen.width/2)
{
transform.position += Vector3.left * carSpeed * Time.deltaTime;
if ( transform.position.x < -4.2f )
{
transform.position = new Vector3(-4.2f, transform.position.y, transform.position.z);
}
}
else if(touch.position.x > Screen.width/2)
{
transform.position += Vector3.right * carSpeed * Time.deltaTime;
if ( transform.position.x > 4.2f )
{
transform.position = new Vector3(4.2f, transform.position.y, transform.position.z);
}
}