$3-25$

An elevated expressway goes through an urban area and crosses a local street as shown in Figure $3\mathrm{.}9.$ The partial cloverleaf exit ramp is on a $2$ percent downgrade, and all vehicles leaving the expressway must stop at the intersection with the local street. Determine $($a$)$ minimum ramp radius and $($b$)$ length of the ramp for the following conditions:

Maximum speed on expressway $=96k\frac{m}{h}$

Distance between exit sign and exit ramp $=78m$

Letter height of road sign $=75mm$

Perception$-$reaction time $=2\mathrm{.}5s$

Maximum superelevation $=0\mathrm{.}08$

Expressway grade $=0\%$

Assume that a driver can read a road sign within his or her area of vision at a distance of $15$ m for each $25$ mm of letter height, and the driver sees the stop sign immediately on entering the ramp.

Figure $3\mathrm{.}9$ Layout of Elevated Expressway Ramp, and Local Street for Problem $3-25$