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Table 3 Examples of SSD restrictions on horizontal curves, based on AASHTO SSD design values (SSD ≤ L), Case 1

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)* 188 287 440 667 891 1260 1628
Calculated radius (m): desirable (HSO = 3.0 m) * 301 459 704 1067 1426 2017 2604
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 ** 66 80 94 108 123 139 160
AB: Available SSD (m), HSO = 3.0  m, R = Rmin** 52 63 74 85 97 110 127
  1. Clarifications:
  2. SSD (m): demanded stopping sight distance based on Eq. 1. Its design values are adopted from AASHTO [2].
  3. Calculated radius-desirable (m): horizontal radius derived by horizontal sightline offset (HSO) and SSD according to Eq. 6.
  4. Minimum radius (Rmin), (m): minimum horizontal radius derived from equilibrium concept (Eq. 2). Its design values are adopted from AASHTO [2].
  5. AB (m): Available SSD derived by the minimum radius (Rmin) and HSO, according to Eq. 6a.
  6. * Calculated radius for desirable SSD: R (desirable) = SSD2 / (8·HSO), for SSD ≤ L, based on Eq. 6
  7. **Calculated AB for Rmin: \( A{B}_{Available}=\sqrt{HSO\cdot 8\cdot {R}_{\min }} \), for SSD ≤ L, based on Eq. 6a