11.3.4 Two-lane Entry
Figure 11.7(b) shows a two-lane entry ramp with two lanes at the nose. It should be appreciated that Figure 11.7 and Table 11.2 apply to situations where a curve that has a design speed less than the design speed of the through road is provided just in advance of the nose. Whilst these situations arise in practice, it is preferable that the alignment and length of the on-ramp is sufficient to enable cars to be travelling at the design speed of the through road when they are at the nose, and that an entry treatment that complies with the relevant road agency guidelines is provided. AGRD Part 4A (Austroads 2010a) should be used to assess the length of ramp required for acceleration to the design speed of the through road.
The key feature of this arrangement is that the right lane of the entry ramp is directed into an added lane on the freeway downstream of the interchange. This added lane should continue for a considerable distance downstream to enable the combined ramp flow to stabilise prior to merging with the through traffic on the major road.
The left lane of the two-lane ramp is treated in the same way as a single-lane entry but in this case traffic from this lane merges with traffic from the right-hand lane of the ramp.