High-speed terminals are intended for use on all facilities with a design speed of
50 mi/h (80 km/h) or higher. They are used in both rural and urban locales. Figure 2.41
shows the details for high-speed single-lane entrance terminals. This terminal is a
taper-type design for the last 1250 ft (381 m), tapering from a 25-ft (7.6-m) offset
from the mainline to zero. Tables A and B in Fig. 2.41 provide information for
designing the length of the terminal to provide adequate distance for entering vehicles
that matches or nearly matches the design speed of the mainline. This must be
achieved by the time the terminal narrows to 12 ft (3.7 m) in width (see Fig. 2.41).
Figure 2.42 provides design information for high-speed single-lane exit terminals
that are used in both rural and urban locales. In the urban environment, a sharper
departure curve is permitted for the exit curve, which allows for a slower speed exit.
Once again, Tables A and B are provided in Fig. 2.42 to determine the proper terminal
length based on mainline speed, first curve speed, and vertical grade adjustment.