Vehicle going through objects

I am currently creating a game which involves a car. I am testing the car and I have a script to make the car move using WASD. But when I try to go up a ramp or something that isn't at the level the car is set at, it will just go straight through it like it has no colliders. I am also very knew to this.

Here is my code

using UnityEngine; using System.Collections;

public class CARSCRIPT : MonoBehaviour { public float forwardSpeed = 40.0f; public float backwardSpeed = 20.0f; public float rotateSpeed = 80.0f;

 // Use this for initialization 
 void Start()
 {

 }

 // Update is called once per frame 
 void Update()
 {
     if (Input.GetKey(KeyCode.S))
     {
         transform.position -= transform.forward * forwardSpeed * Time.deltaTime;
     }
     if (Input.GetKey(KeyCode.W))
     {
         transform.position += transform.forward * backwardSpeed * Time.deltaTime;
     }
     if (Input.GetKey(KeyCode.S))
     {

         if (Input.GetKey(KeyCode.D))
         {
             transform.Rotate(0.0f, -rotateSpeed * Time.deltaTime, 0.0f);
         }
         if (Input.GetKey(KeyCode.A))
         {
             transform.Rotate(0.0f, rotateSpeed * Time.deltaTime, 0.0f);
         }
     }
     else if (Input.GetKey(KeyCode.W))
     {
         if (Input.GetKey(KeyCode.D))
         {
             transform.Rotate(0.0f, rotateSpeed * Time.deltaTime, 0.0f);
         }
         if (Input.GetKey(KeyCode.A))
         {
             transform.Rotate(0.0f, -rotateSpeed * Time.deltaTime, 0.0f);
         }
     }
 }

}