Appendix E 4.1 Description and Input Data for Design 2
The proposed intersection layout (Design 2) is shown in Figure E 6. It is similar to that of Design 1, with the exception of the following changes made to the North approach:
- An exclusive right turn lane 2.8 m wide and 70 m long (short lane) is provided.
- The median strip is reduced from 4.5 m to 1.7 m wide.
- A left turn slip lane 3.0 m wide and 80 m long (short lane) is provided.
- The pedestrian crossing between the footpath and the traffic island is not signalised. If a Zebra (unsignalised) crossing is used, the effect on left turns using the slip lane could be analysed using SIDRA INTERSECTION.
The proposed signal phasing system is shown in Figure E 7. Because the exclusive right turn lane added to the North approach will be arrow controlled, a leading right turn sequence is used as the opposing filter right turn has been retained (Phase C added). A lagging right turn sequence has safety problems in this case (Section 6.5.3). Had the right turn volume from the South approach been considerably higher, a diamond overlap phase design would have been assessed (Section 6.5.3). This would have required an exclusive right turn lane to be provided on the South approach as well.
The left turn movement from north (slip lane) gives way to right turns from south in Phase A, and to through traffic from west in Phase B. This movement is designated as undetected, and therefore, will not affect signal timings.
The right turn movement from north receives two distinct green periods, namely unopposed during Phase C and opposed during Phase A, stopping during the intergreen time between Phases C and A. On the other hand, the through movement from north has a single green period although it runs during both Phases C and A (it is not stopped during the intergreen time between Phases C and A). However, if the design permitted Phase A to be skipped allowing signal control to change from Phase C to Phase B, then adequate clearance should be provided during Phase C for both the North Right Turn and North Through movements. This may require further consideration on a site‑by-site basis.
The intergreen time for Phase C is calculated on the basis of the conflict between the right turn movement from North clearing the intersection and the pedestrian movement in front of the West approach starting. Negotiation radius for this movement is measured as 15 m, and the distance is calculated as 24 m.
Using tr = 1.0 s, ad = 3.0 m/s2, vD = 60 km/h and G = –0.07 in Equation A2, yellow time is calculated as ty = 4.6 s. Using LC = 24 m in Equation A3, all-red time (for 60 km/h zone) is found as tar = 1.4 s. The following values are used as input (rounded to the nearest half second):
- Phase A (North - South movements): ty = 5.0 s, tar = 1.0 s
- Phase B (East-West movements): ty = 4.0 s, tar = 1.5 s
- Phase C (North Leading Right Turn): ty = 5.0 s, tar = 1.5 s.
Thus, Intergreen Times are 6.0 s (I = ty+ tar) for the North-South movements, 5.5 s for the East‑West movements and 6.5 s for the North Leading Right Turn.
Minimum green times for Phases A and B are 8 seconds as in Design 1, and minimum green time for Phase C is chosen as 6 seconds (Table G 1). Minimum pedestrian time requirements are not changed as a result of the changes to intersection geometry.
The additional start loss of 8 seconds is removed from the left turn movement from North. It is retained for the right turn movement from North in Phase A, but there is no additional start loss for this movement in Phase C.
For Phase C (arrow-controlled right turn), maximum green setting = 20 seconds and gap setting = 2.0 seconds will be applicable (default values). Signal coordination data are unchanged.