Varaiable speed limit for automotive

1#include <Wire.h>
2#include <LiquidCrystal_I2C.h>
3LiquidCrystal_I2C  lcd(0x27, 16 , 2);
4#define trigPin 2   
5#define echoPin 3
6const int IN1  = 8;
7const int IN2 = 9;
8const int IN3 = 7;
9const int IN4 = 6;
10const  int ENA = 10;
11const int ENB = 5;
12long duration, distance, meter ; 
13
14void  setup() {
15  Serial.begin (9600);
16   lcd.begin();
17  // Turn on the blacklight  and print a message.
18  lcd.backlight();
19  lcd.print("distance cms");
20  pinMode(trigPin, OUTPUT);
21  pinMode(echoPin, INPUT);
22  pinMode (IN1, OUTPUT);
23  pinMode (IN2, OUTPUT);
24  pinMode (IN3, OUTPUT);
25  pinMode (IN4, OUTPUT);
26  pinMode (ENA, OUTPUT);
27  pinMode (ENB, OUTPUT);
28
29}
30
31void loop()  
32{
33  
34  digitalWrite(trigPin, LOW);
35  delayMicroseconds(2);
36  digitalWrite(trigPin,  HIGH);
37  delayMicroseconds(10);
38  digitalWrite(trigPin, LOW);
39  distance  = pulseIn(echoPin, HIGH);
40  meter = (distance*0.034)/2.0;// measure distance     
41  Serial.println(meter);
42   String disp = String (distance);
43  lcd.clear();  
44  lcd.setCursor(0,1);
45  lcd.print(disp);
46  lcd.print(distance); 
47  lcd.print("  m");        
48  delay(100);
49  
50if(meter>30)
51{
52//control speed 
53  analogWrite(ENA, 225);
54  analogWrite(ENB, 225);            
55  digitalWrite(8,HIGH);                             
56   digitalWrite(9,LOW);                             
57   digitalWrite(7,LOW);                            
58   digitalWrite(6,HIGH);                              
59 }
60 
61  else if(meter>20) { 
62    
63  //control speed 
64  analogWrite(ENA, 100);
65  analogWrite(ENB, 100); 
66   digitalWrite(8,HIGH);
67   digitalWrite(9,LOW);
68   digitalWrite(7,LOW);                                  
69   digitalWrite(6,HIGH);
70  }
71   else if(meter<10) { 
72    
73  //control  speed 
74  analogWrite(ENA, 0);
75  analogWrite(ENB, 0); 
76   digitalWrite(8,LOW);
77   digitalWrite(9,LOW);
78   digitalWrite(7,LOW);                                  
79   digitalWrite(6,LOW);
80
81}
82}
83