Lithgow Zig Zag was listed on the New South Wales State Heritage Register on 2 April 1999 having satisfied the following criteria. The place is important in demonstrating the course, or pattern, of cultural or natural history in New South Wales. It is of historical significance because upon completion it triggered extensive development and had a profound influence on the economy of western New South Wales. It contributed to the economy of western New South Wales to such an extent that it could not handle the volume of traffic and had to be replaced. The place is important in demonstrating aesthetic characteristics and/or a high degree of creative or technical achievement in New South Wales. The reserve is a fine scenic attraction in itself, offering superb views of the rugged sandstone valleys and escarpments leading to the western plains. It serves to provide a dramatic juxtaposition to the urban development of nearby Lithgow suburbs. The three main viaducts are particularly pleasing structures. The place has a strong or special association with a particular community or cultural group in New South Wales for social, cultural or spiritual reasons. It reflects the difficulty experienced in crossing the Blue Mountains and engineering compromises enforced by economics. The place has potential to yield information that will contribute to an understanding of the cultural or natural history of New South Wales. At the time of building the Great Zig Zag Railway was regarded as the greatest civil engineering work in Australia at that time and attracted worldwide interest as an engineering marvel.