Problems with HC-SR04 sensor toy car project

Other Hardware Sensors
1

I have made a project for a car that will drive through the hallways of my school. I have set up the code to use three sensors located at the front, left, and right of the car to monitor how close the car is to the walls. I an controlling the steering part of the car using a servo motor that is set correctly to turn in the right direction for adjusting the car into a better location with all the turn methods. When the front sensor receives a distance of less than 6 feet the car should turn completely. If the side sensors receive a distance less than 1 1/2 feet then the car should adjust back to the middle. The problem that I am currently facing is the sensors are turning when that are no objects within the threshold of the set dimensions. I followed the code similar to the example sketch on the New Ping library page. On the page the code handles out of bounds exceptions but for some reason the sensors I have are not handling that. Help would be immensely appreciated. Here is the code:

#include <NewPing.h>
#include <Servo.h>

#define SONAR_NUM     3 // Number or sensors
#define PING_INTERVAL 50  // Milliseconds between pings.
unsigned long pingTimer[SONAR_NUM]; // When each pings.
uint8_t currentSensor = 0; // Which sensor is active.

// Front sensor information
#define sensorPinFront 11
#define ledForFront 5
long durationFront;
long distanceFront; 

// Left sensor information
#define sensorPinLeft 12
#define ledForLeft 6 
long durationLeft;
long distanceLeft;

// Right Sensor Information
#define sensorPinRight 13
#define ledForRight 7
long durationRight;
long distanceRight;

// Boolean values for turning
bool sensorActivated;

//Servo controlling front turns with servo signal pin
Servo servo;
#define servoPin 2

//Sensor distance value array
int sonarDistances[SONAR_NUM]; 
int sonarTime[SONAR_NUM];

// Sensor object array.
NewPing sonar[SONAR_NUM] = 
{ 
  NewPing(sensorPinFront, sensorPinFront, 350),
  NewPing(sensorPinLeft, sensorPinLeft, 350),
  NewPing(sensorPinRight, sensorPinRight, 350)
};

void setup() {
  Serial.begin(9600);
  servo.attach(servoPin);
  servo.write(90);
  
  pingTimer[0] = millis() + 75; // First ping start in ms.
  for (uint8_t i = 1; i < SONAR_NUM; i++)
  {
    pingTimer[i] = pingTimer[i - 1] + PING_INTERVAL;
  }
}

void echoCheck() { // If ping echo, set distance to array.
  if (sonar[currentSensor].check_timer()){
    sonarTime[currentSensor] = sonar[currentSensor].ping_median(5, 350); 
    sonarDistances[currentSensor] = sonar[currentSensor].convert_in(sonarTime[currentSensor]);
  }
}

void distanceChecks(){
  distanceFront = sonarDistances[0];
  distanceLeft = sonarDistances[1];
  distanceRight = sonarDistances[2];
  sensorActivated = false;
  
  if (distanceFront < 72 && !sensorActivated) //84
  {
    sensorActivated = true;
    digitalWrite(ledForFront, HIGH);   
    longRightTurn();
  }
  else
  {
    sensorActivated = false;
    digitalWrite(ledForFront, LOW); 
  }

  if (distanceFront >= 72 || distanceFront == 0 || distanceFront < 0)
  {
    // Out of range setting
    sensorActivated = false;
    digitalWrite(ledForFront, LOW);
  }
 
  if (distanceLeft < 18 && !sensorActivated) //18
  {
    sensorActivated = true;
    digitalWrite(ledForLeft, HIGH); 
    shortRightTurn();
  }
  else 
  {
    sensorActivated = false;
    digitalWrite(ledForLeft, LOW); 
  }
  
  if (distanceLeft >= 18 || distanceLeft == 0 || distanceLeft < 0)
  {
    // Out of range setting
    sensorActivated = false;
    digitalWrite(ledForLeft, LOW);
  }
  
  
  if (sonarDistances[2] < 18 && !sensorActivated) //18
  {
    sensorActivated = true;
    digitalWrite(ledForRight, HIGH); 
    shortLeftTurn();
  }
  else 
  {
    sensorActivated = false;
    digitalWrite(ledForRight, LOW); 
  }

  if (distanceRight >= 18 || distanceRight == 0 || distanceRight < 0)
  {
    // Out of range setting 
    sensorActivated = false;
    digitalWrite(ledForRight, LOW);
  }
}

void stayStraight(){
  servo.write(90);
  delay(500);
  servo.write(66.25);
  delay(500);
}

void shortLeftTurn(){
  servo.write(180);
  delay(2500);
  servo.write(0);
  delay(2500);
  sensorActivated = false;
}

void shortRightTurn(){
  servo.write(0);
  delay(2500);
  servo.write(180);
  delay(2500);
  sensorActivated = false;
}

void longRightTurn(){
  servo.write(0);
  delay(3000);
  sensorActivated = false;
}

void loop() {
  for (uint8_t i = 0; i < SONAR_NUM; i++) { // Loop through all the sensors
    if (millis() >= pingTimer[i]) {         // Is it this sensor's time to ping?
      pingTimer[i] += PING_INTERVAL * SONAR_NUM;  // Set next time this sensor will be pinged.
      if (i == 0 && currentSensor == SONAR_NUM - 1) // Sensor ping cycle complete, do something with the results.
      {
        // Perform distance checks on the specified sensors
        distanceChecks();
      }
      sonar[currentSensor].timer_stop();  // Make sure previous timer is canceled before starting a new ping (insurance).
      currentSensor = i;                  // Sensor being accessed.
      sonarDistances[currentSensor] = 0;  // Make distance 0 in case there is no ping echo for the sensor
      sonar[currentSensor].ping_timer(echoCheck); // Do the ping (processing continues, interrupt will call echoCheck to look for echo).
    }
  }

  stayStraight();
}