Appendix E 3.1 Description and Input Data for Design 1
The current intersection layout (Design 1) is shown in Figure E 1. The North-South road (Main Road) has three-lane approaches with median and clearway conditions, whereas the East‑West road (Side Street) has two-lane approaches without median and with parking allowed up to 60 m from the stop line (corresponding short lane lengths of 50 m are specified). All approaches have shared left turn and right turn lanes, and all lanes have normal stop lines (no slip lanes or continuous lanes).
Signalised crossings exist in front of all intersection legs except South. Other details such as lane widths, grades, kerb-to-kerb road widths, electric supply pole (ESP), electric light pole (ELP) and so on are shown in Figure E 1 .
The existing intersection is two-phase operation with filter right turns as shown in Figure E 2. Peak hour traffic volumes for each approach and pedestrian volumes for each crossing are shown in Figure E 3.
The filter right turn movements from both North and South approaches encounter heavy opposing flows, and the right turn movement from North has high volume.
The site has a crash history of eight right-angle collisions and two ‘right turn with opposing-through’ collisions, and the number of crashes has been increasing in recent years. This trend is in line with increased right turn volume from the North resulting from the expansion of the shopping centre.
The two-phase arrangement can no longer cater for right turn volumes against heavy opposing through traffic flows, as evident by very long delays experienced by right turning vehicles from the North approach in particular. The current conditions (Design 1) will be analysed with this problem in mind, and then improvements to the intersection layout and signal phasing will be sought in order to improve the intersection safety and efficiency substantially (Design 2) as discussed in Part 6 of the Guide to Traffic Management (Austroads 2019c).
Various input data for Design 1 analysis are determined as follows:
- The volumes in Figure E 3 are peak 30-minute values though given as hourly flow rates (i.e. twice the values of 30-minute volume counts). Therefore, Unit Time for Volumes is specified as 60 minutes, Peak Flow Period for performance calculations is specified as 30 minutes, and the Peak Flow Factor values are specified as 1.00.
- There are no measured saturation flows available, and hence they will be estimated by the program. The site is in a suburban shopping environment. Basic saturation flows of 1950 and 1800 through car units per hour are considered to be appropriate for the North-South and East‑West roads, respectively.
- Due to wide median strips on South and North approaches, Free Queue values of 1 vehicle are specified for right turns in shared lanes. This means that one vehicle can queue away from the lane without interrupting the flow of the through movement which shares the lane (the second right turning vehicle would block the through traffic).
- The intersection is in a 60 km/h speed limit zone. All approach and exit speeds are therefore specified as 60 km/h. All approach distances are specified as 500 m.
- Yellow Time and All-Red Time values are determined using the method described in Appendix G.4.6. Yellow Times (ty) are calculated using Equation A2 with vD = 60 km/h, tr = 1.0 s, ad = 3.0 m/s2 and the grades shown in Figure E 1. The resulting Yellow Times are calculated as ty = 4.3 s for South, 4.6 s for North, 3.8 s for East and 3.5 s for West approaches. Intersection widths used for All-Red Time (tar) calculations are 13 m for North‑South movements and 25 m for East-West movements, and the corresponding All‑Red Times from Equation A3 are tar = 0.8 and 1.5 s, respectively. The following values are used as input (rounded to 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
Thus, Intergreen Times are 6.0 seconds (I = ty+ tar) for the North-South movements and 5.5 s for the East-West movements.
- The minimum green times are 8 seconds for Phases A and B (Table G 1), subject to pedestrian minimum time requirements discussed in point 8 below. Normal start loss values are 3 seconds. Left turning and right turning vehicles that conflict with pedestrian movements are assumed to experience a further 8 seconds delay. Therefore, the start loss values for turning vehicles (except left turns from East and right turns from West) will be 11 seconds. This will impact traffic performance significantly but will have less effect on right turn traffic since start losses due to opposing traffic queue clearance intervals are longer than 11 seconds.
- The pedestrian Walk Time is selected as 6 seconds for all movements (Walk Times are not extended with parallel vehicle green times). The pedestrian clearance times are determined by SIDRA INTERSECTION using Equation A5 with pedestrian clearance speed of 1.2 m/s (default). Clearance distances of 14 m for North-South movements and 26 m for East-West movements (including both carriageways and the median width as applicable) are specified.
- Minimum time requirements for pedestrians are determined as the sum of Walk Time and Clearance 1 Time (Figure G 2). Clearance 1 Time is determined as the Total Clearance Time less Clearance 2 Time (overlap with the Intergreen Time). The SIDRA INTERSECTION default value of 2 seconds Clearance 2 Time is used.
- The resulting ‘Pedestrian Minimum Green’ times are 16 seconds for North-South movements and 26 seconds for East-West movements. The SIDRA INTERSECTION method for actuated signals may use a smaller ‘average’ minimum pedestrian time requirement so as to allow for signal cycles with no pedestrian demand. This is likely to come into effect with low pedestrian volumes on the crossings in front of the East and West approaches.
- Default values of actuated signal settings (maximum green and gap settings) will be used. Effective detection zone length is 4.5 m for all lanes. Due to the phasing arrangement without any arrow-controlled right turns in Design 1, Maximum Green Setting = 50 seconds and Gap Setting = 2.5 seconds will be used for all movements.
- Actuated coordinated signals are assumed. Arrival types of 5 (‘Highly favourable’ progression quality) for the through movement on the North approach, and 4 (‘Favourable’ progression quality) for the through movement on the South approach are specified.