How do I limit the speed of my car?

I am making a car game and i cannot limit the speed, but it the speed just goes unlimited. Below is the code which is not limiting my speed and converts the speed to kmph.

  function Control (){
     currentSpeed = 2*22/7*WheelRL.radius*WheelRL.rpm*60/1000; //this converts the speed to kmph
     currentSpeed = Mathf.Round(currentSpeed); //this converts the speed to kmph
     if (currentSpeed < topSpeed && currentSpeed > -maxReverseSpeed){ //these lines limit my speed
     WheelRR.motorTorque = maxTorque * Input.GetAxis("Vertical");
     WheelRL.motorTorque = maxTorque * Input.GetAxis("Vertical");
     }
     else {
     WheelRR.motorTorque =0;
     WheelRL.motorTorque =0;
     }

Below is my whole car control code:-

 #pragma strict
 
 var WheelFL : WheelCollider;
 var WheelFR : WheelCollider;
 var WheelRL : WheelCollider;
 var WheelRR : WheelCollider;
 var WheelFLTrans : Transform;
 var WheelFRTrans : Transform;
 var WheelRLTrans : Transform;
 var WheelRRTrans : Transform;
 var lowestSteerAtSpeed : float = 50;
 var lowSpeedSteerAngel : float = 20;
 var highSpeedSteerAngel : float = 5;
 var decellarationSpeed : float = 30; 
 var maxTorque : float=50;
 var currentSpeed : float;
 var topSpeed : float = 150;
 var maxReverseSpeed : float = 50;
 var backLightObject : GameObject;
 var idleLightMaterial : Material;
 var brakeLightMaterial : Material;
 var reverseLightMaterial : Material;
 private var mySidewayFriction : float;
 private var myForwardFriction : float;
 private var slipSidewayFriction : float;
 private var slipForwardFriction : float;
 
 function Start () {
 rigidbody.centerOfMass.y = -0.9;
 }
 
 function SetValues (){
 myForwardFriction  = WheelRR.forwardFriction.stiffness;
 mySidewayFriction  = WheelRR.sidewaysFriction.stiffness;
 slipForwardFriction = 0.05;
 slipSidewayFriction = 0.085;
 }
 
 function FixedUpdate () {
 Control();
 }
 
 function Control (){
 currentSpeed = 2*22/7*WheelRL.radius*WheelRL.rpm*60/1000; //this converts the speed to kmph
 currentSpeed = Mathf.Round(currentSpeed); //this converts the speed to kmph
 if (currentSpeed < topSpeed && currentSpeed > -maxReverseSpeed){ // this line and the below lines is the code which limits my speed
 WheelRR.motorTorque = maxTorque * Input.GetAxis("Vertical");
 WheelRL.motorTorque = maxTorque * Input.GetAxis("Vertical");
 }
 else {
 WheelRR.motorTorque =0;
 WheelRL.motorTorque =0;
 }
 
 if (Input.GetButton("Vertical")==false){
 WheelRR.brakeTorque = decellarationSpeed;
 WheelRL.brakeTorque = decellarationSpeed;
 }
 else{
 WheelRR.brakeTorque = 0;
 WheelRL.brakeTorque = 0;
 }
 
 WheelRR.motorTorque = maxTorque * Input.GetAxis("Vertical");
 WheelRL.motorTorque = maxTorque * Input.GetAxis("Vertical");
 WheelFR.steerAngle = 20 * Input.GetAxis("Horizontal");
 WheelFL.steerAngle = 20 * Input.GetAxis("Horizontal");
 
 var speedFactor = rigidbody.velocity.magnitude/lowestSteerAtSpeed;
 var currentSteerAngel = Mathf.Lerp(lowSpeedSteerAngel,highSpeedSteerAngel,speedFactor);
 currentSteerAngel *= Input.GetAxis("Horizontal");
 WheelFL.steerAngle = currentSteerAngel;
 WheelFR.steerAngle = currentSteerAngel;
 }
 
 function Update(){
 WheelFLTrans.Rotate(WheelFL.rpm/60*360*Time.deltaTime,0,0);
 WheelFRTrans.Rotate(WheelFR.rpm/60*360*Time.deltaTime,0,0);
 WheelRLTrans.Rotate(WheelRL.rpm/60*360*Time.deltaTime,0,0);
 WheelRRTrans.Rotate(WheelRR.rpm/60*360*Time.deltaTime,0,0);
 WheelFLTrans.localEulerAngles.y = WheelFL.steerAngle - WheelFLTrans.localEulerAngles.z;
 WheelFRTrans.localEulerAngles.y = WheelFR.steerAngle - WheelFRTrans.localEulerAngles.z;
 BackLight();
 }
 
 function BackLight (){
 if (currentSpeed > 0 && Input.GetAxis("Vertical")<0){
 backLightObject.renderer.material = brakeLightMaterial;
 }
 else if (currentSpeed < 0 && Input.GetAxis("Vertical")>0){
 backLightObject.renderer.material = brakeLightMaterial;
 }
 else if (currentSpeed < 0 && Input.GetAxis("Vertical")<0){
 backLightObject.renderer.material = reverseLightMaterial;
 }
 else{
 backLightObject.renderer.material = idleLightMaterial;
 }
 }