Summit curve +4% and -4%, limited to 800 m

$g_1=+4\%,\ g_2=-4\%$, so $N=0.08$. This is a summit curve (IRC/NRS 2070: eye height 1.2 m; object height 0.15 m for SSD and 1.2 m for OSD).

(a) Stopping sight distance S = 150 m

Assuming $L>S$:

$$L=\frac{NS^2}{4.4}=\frac{0.08(150)^2}{4.4}=409.1\ \text{m}$$

$L>S$, so valid. L ≈ 410 m, which is less than 800 m, so it is possible.

(b) Overtaking sight distance S = 500 m

For $h_1=h_2=1.2$ m:

$$L=\frac{NS^2}{9.6}=\frac{0.08(500)^2}{9.6}=2083.3\ \text{m}$$

This exceeds the 800 m limit. With L = 800 m the sight distance actually available is

$$S=\sqrt{\frac{9.6L}{N}}=\sqrt{\frac{9.6(800)}{0.08}}=309.8\ \text{m}$$

which is much less than the 500 m OSD.

Intermediate sight distance

ISD $=2\times SSD=300$ m:

$$L=\frac{0.08(300)^2}{9.6}=750\ \text{m}$$

This is within 800 m, so ISD can be provided.

Discussion

Answer: adopt L = 800 m (or at least 750 m). It satisfies SSD (210 m available) and ISD (310 m), but full OSD cannot be provided within 800 m. Overtaking must be prohibited on this summit (no-overtaking signs and continuous centre line).