8.1.23 Tunnels
Development of highways and freeways may include sections constructed in tunnels to either carry the roadway under or through a natural obstacle or to minimize the effect of the roadway on the community. General conditions under which tunnel construction may be warranted include:
- Long, narrow terrain ridges where a cut section may either be more costly or carry environmental consequences;
- Narrow ROW where all of the surface area is needed for street purposes;
- Large intersection areas or a series of adjoining intersections on an irregular or diagonal street pattern;
- Grade-separated pedestrian and/or bicycle facilities are needed;
- Railroad yards, airport runways, or similar facilities;
- Parks or similar land uses (existing or planned); or
- Locations where ROW acquisition costs exceed cost of tunnel construction and operation.
Specific design parameters such as soil conditions, construction phasing, ventilation, drainage, lighting, pumping, and other mechanical or electrical components should be considered as a part of the design of highway tunnels. For further information on the design of tunnels, refer to
.