def create(self, source, destination, gateway_ip, comment=None):
        """
        Add a new policy route to the engine.
        
        :param str source: network address with /cidr
        :param str destination: network address with /cidr
        :param str gateway: IP address, must be on source network
        :param str comment: optional comment
        """
        self.items.append(dict(
            source=source, destination=destination,
            gateway_ip=gateway_ip, comment=comment))