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Table 4 Examples of SSD restrictions on horizontal curves, based on AASHTO SSD design values (SSD = 2·L), Case 2

From: Sight distance restriction on highways’ horizontal curves: insights and sensitivity analysis

SSD restrictions Design speed, Vd (km/h)
60 70 80 90 100 110 120
Stopping sight distance, SSD (m), AASHTO [2] 85 105 130 160 185 220 250
Calculated radius (m): desirable (HSO = 4.8 m)* 141 215 330 500 668 945 1221
Calculated radius (m): desirable (HSO = 3.0 m) * 226 345 528 800 1070 1513 1953
Minimum radius, Rmin (m), equilibrium concept, e(max) = 8 %, [2] 113 168 229 304 394 501 667
AB Available SSD (m) HSO = 4.8 m, R = Rmin ** 72 88 100 113 128 142 165
AB Available SSD (m) HSO = 3.0  m, R = Rmin** 53 65 75 86 97 110 127
  1. Clarifications:
  2. See clarifications of Table 3 for SSD and Rmin.
  3. Calculated radius-desirable (m): horizontal radius derived by horizontal sightline offset (HSO) and SSD according to Eq. 10.
  4. AB (m): Available SSD derived by the minimum radius (Rmin) and HSO, according to Eq. 10a.
  5. *Calculated desirable radius for SSD: \( {R}_{Desirable}=\frac{L\cdot \left(2\cdot SSD-L\right)}{8\cdot HSO} \), for SSD > L, based on Eq. 10
  6. **Calculated AB for Rmin: \( A{B}_{Available}=\frac{(HSO)\cdot 4\cdot {R}_{\min }}{L}+\frac{L}{2} \), for SSD > L, based on Eq. 10a