
    Write a function that validates delivery route identifiers in the fleet management system by checking if they follow the required lowercase-underscore naming format. The function should return true if the route identifier contains only lowercase letters joined by underscores (like "north_route_b"), and false for any other format.
    

    
import re

def text_lowercase_underscore(text):
    """
    Write a function that validates delivery route identifiers in the fleet management system by checking if they follow the required lowercase-underscore naming format. The function should return true if the route identifier contains only lowercase letters joined by underscores (like "north_route_b"), and false for any other format.
    

    """
import re

def text_lowercase_underscore(text):
    """
    Write a function that validates delivery route identifiers in the fleet management system by checking if they follow the required lowercase-underscore naming format. The function should return true if the route identifier contains only lowercase letters joined by underscores (like "north_route_b"), and false for any other format.
    

    """
    patterns = '^[a-z]+_[a-z]+$'
    if re.search(patterns, text):
        return True
    else:
        return False