10.6 SETTING-OUT DATA

Figure 10.28 indicates the usual situation of two straights projected forward to intersect at I with a clothoid transition curve commencing from tangent point T ₁ and joining the circular arc at t ₁. The second equal transition commences at t ₂ and joins at t ₂. Thus the composite curve from T ₁ to T ₂ consists of a circular arc with transitions at entry and exit.

1. Fixing the tangent points T ₁ and T ₂

   In order to fix T ₁ and T ₂ the tangent lengths T ₁ I and T ₂ I are measured from I back down the straights, or they are set out direct by coordinates.

   (10.18)

   The values of S and C are abstracted from the Highway Transition Curve Tables ( Metric) (see Table 10.2).

2. Setting out the transitions

   Referring to Figure 10.29:

   The theodolite is set at T ₁ and oriented to I with the horizontal circle reading zero. The transition is then pegged out using deflection angles ( ?) and chords (Rankine's method) in exactly the same way as for a simple curve.

   The data are calculated as follows:

   1. The length of transition L is calculated (see design factors in Section 10.5.5 and 10.5.6), assume L = 100 m.

   2. It is then split into, say, 10 arcs, each 10 m in length (ignoring through chainage), the equivalent chord lengths being...