How to read Ultrasonic sensor value to use and drive servo motors
First, I would make sure I have continuous servo motors that can rotate 360 degrees. Your servos will just rotate to the degree you entered if they are not continuous. Additionally, it would be more helpful if you named your pins. For example:

int echo = 7;
void setup(){
    pinMode(echo, INPUT);
}


This will help us read the code better. 

I also see that you have "pulseIn" in your if statement. You must save the value to a variable with the data type of unsigned long. 

//before the setup 
unsigned long duration;

//keep your setup as it is


void loop(){
   digitalWrite(8, LOW); 
   delayMicroseconds(2); 
   digitalWrite(8, HIGH);
   delayMicroseconds(10);  
   digitalWrite(8, LOW); 

   duration=pulseIn(echo, HIGH);

   if(duration&lt;=400){//check for the value
       // turn LED on:
        digitalWrite(13, HIGH);
        // turn the motors off for 2 seconds
        motor1.write(90);
        motor2.write(90);
        delay(2000);
        //turn motor 1 on for 2 seconds to make a turn
        motor1.write(180);
        delay(2000);
   }else{
        digitalWrite(13, LOW);
        //motors run when vehicle is not near objects
         motor1.write(0);
         motor2.write(180);
       }
   }


Overall: check your servos and save the value of pulseIn to a variable. You might also want to convert to centimeters by dividing duration by 58.2.