Vertical curve design insights of road tunnels versus highways

ABSTRACT

The design of road tunnels is an essential infrastructure component in the highway system. The study implements reasonable criteria for obtaining vertical curve length based on sight distance requirements of road tunnels versus open roadways. The infrastructure impact of sight distance tunnel characteristics on the design of crest and sag vertical curve radii is based on safety and driving comfort criteria. Both results of crest and sag vertical curves show significant reductions of vertical radii in road tunnels compared to open roadways, that is, percentage reduction range of 35% to 71% depending on the design speed, curve type, and tunnel pavement characteristics. The driving comfort criterion generally overrides in the lower range of design speeds whereas the safety criterion overrides in the upper range of design speeds: 100– to 120 km/h for moist and dry tunnel sag vertical curve, 90 to 120 km/h for dry tunnel crest vertical curve, and 80 to 120 km/h for moist tunnel crest vertical curve.

This impact of a reduced vertical curve length triggers the possibility of shorter tunnel construction length, lower tunnel construction cost and maintenance cost including components of complementary systems, and flexibility in tunnel construction due to geotechnical, groundwater, and other infrastructure constraints. Still, the selected tunnel alignment, even if it is shorter than other alternatives, requires field tests such as geological investigation, vibrations and building inspection, and hydrologic balance.

KEYWORDS:

• crest
• sag
• road tunnel
• sight distance
• trucks
• vertical curve