Need help making only one car drive at a time

I am making an open world game and a want the ability for the player to get in a random vehicle and only that one to drive but currently they all drive lol

using UnityEngine; using System.Collections;

public class VehicleController : MonoBehaviour { public float maxTorque = 1000f; GameObject player;

 public Transform centerOfMass;

 public WheelCollider[] wheelColliders = new WheelCollider[4];

 private Rigidbody m_rigidbody;

 public bool inCar = false;
 public bool driving = false;

 void Start()
 {
     player = GameObject.Find ("Player");
     m_rigidbody = gameObject.GetComponent<Rigidbody> ();
     m_rigidbody.centerOfMass = centerOfMass.localPosition;
 }
 void Update()
 {
     if (Input.GetKeyDown (KeyCode.H)) {
         if (((player.GetComponent<PlayerController> ().withinRange == true) || inCar == true)) {
             putPlayerInCar ();
         }
     }

 }
 void putPlayerInCar()
 {
     inCar = !inCar;
     if (inCar == true) {
         GameObject.Find ("Main Camera").GetComponent<SmoothFollow> ().target = gameObject.transform;
         player.GetComponent<MeshRenderer> ().enabled = false;
         player.GetComponent<CapsuleCollider> ().enabled = false;
         player.GetComponent<Rigidbody> ().useGravity = false;
     } 
     else 
     {
         player.GetComponent<PlayerController> ().moveCameraToPlayer ();
         player.GetComponent<MeshRenderer> ().enabled = true;
         player.GetComponent<CapsuleCollider> ().enabled = true;
         player.GetComponent<Rigidbody> ().useGravity = true;
         player.transform.position = (gameObject.transform.position + new Vector3(-4,1,0));
         player.transform.rotation = gameObject.transform.rotation;
     }
     player.GetComponent<PlayerController> ().enabled = !player.GetComponent<PlayerController> ().enabled;
 }

 void FixedUpdate()
 {
     if (inCar == true) 
     {
         float steer = Input.GetAxis ("Horizontal");
         float accelerate = Input.GetAxis ("Vertical");
         float finalAngle = steer * 45f;
         wheelColliders [0].steerAngle = finalAngle;
         wheelColliders [1].steerAngle = finalAngle;

         if ((accelerate == 0) && (wheelColliders [0].rpm > 0 || wheelColliders [0].rpm < 0) && Input.GetKey (KeyCode.Space)) {
             wheelColliders [0].brakeTorque = maxTorque * 2;
             wheelColliders [1].brakeTorque = maxTorque * 2;
             wheelColliders [2].brakeTorque = maxTorque * 2;
             wheelColliders [3].brakeTorque = maxTorque * 2;
         } else if (accelerate == 0 && (wheelColliders [0].rpm > 0 || wheelColliders [0].rpm < 0)) {
             wheelColliders [0].brakeTorque = maxTorque / 2;
             wheelColliders [1].brakeTorque = maxTorque / 2;
             wheelColliders [2].brakeTorque = maxTorque / 2;
             wheelColliders [3].brakeTorque = maxTorque / 2;
         } else {
             wheelColliders [0].brakeTorque = 0;
             wheelColliders [1].brakeTorque = 0;
             wheelColliders [2].brakeTorque = 0;
             wheelColliders [3].brakeTorque = 0;
         }
         for (int i = 0; i < 4; i++) {
             wheelColliders [i].motorTorque = accelerate * maxTorque;
         }
     }
 }

}