
    Write a function that validates delivery route identifiers in a fleet management system by checking if the identifier contains only lowercase letters joined with underscores. The function should return true for valid route identifiers like "north_route_b" and false for invalid ones like "North-Route" or "route.1".
    

    
import re

def text_lowercase_underscore(text):
    """
    Write a function that validates delivery route identifiers in a fleet management system by checking if the identifier contains only lowercase letters joined with underscores. The function should return true for valid route identifiers like "north_route_b" and false for invalid ones like "North-Route" or "route.1".
    

    """
import re

def text_lowercase_underscore(text):
    """
    Write a function that validates delivery route identifiers in a fleet management system by checking if the identifier contains only lowercase letters joined with underscores. The function should return true for valid route identifiers like "north_route_b" and false for invalid ones like "North-Route" or "route.1".
    

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