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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