Introduction

The Brittanie Corner intersection has, for the last 50 years, been considered the worst intersection in South Australia. The reasoning for this bold statement was that it contained 5 major arterial roads crossing from west to east and south to north within the Adelaide metropolitan area.

Over the past 50 years, traffic volume has steadily increased causing the Britannia intersection to become of major bottleneck that has not only caused delays but become a major issue in terms of road safety.

It was a psychological barrier for up to 10,000 motorists a day who sought alternative routes to avoid the intersection. It is claimed to have over 100 motor vehicle crashes each year In traffic engineering jargon, it might be described as both a ‘black spot’ (traffic safety) and a ‘red spot’ (traffic congestion). A number of alternative schemes for upgrading the intersection have been considered in the last decade; in 2013 this problem has been considered as fixed with a new design.

The aim of this study is the make a comparison between the Britannia roundabout of old, pre 2013, and the current Britannia roundabout that has supposedly solved these traffic problems. There has been supplied traffic data of the Britannia roundabout prior to its redevelopment, this data will allow us to interpret what the conditions were like and comprehend where the major areas of concern are within the confines of traffic engineering.

We will be re-examining the intersection to see if the new design is an improvement on traffic congestion and road safety. Based on the findings from the analysis of the previous design, the intersection that had the most adverse conditions will be chosen; if multiple intersections suffered then they will also be considered.

Figure 1: New Development of the Britannia Roundabout

Traffic Analysis

In order for us to compare the Britannia roundabout pre and post 2013, we must analyse the historical data that has been provided from the Department of Transport and Infrastructure (DPTI) and our own data collected in 2015.

The historical data for the old Britannia roundabout was conducted in 1998-2002 by DPTI, they reference several forms of data collection that will allow us to perform an in depth analysis of not only Britannia roundabout but surrounding intersections such as Greenhill rd/Fullarton rd and Dequetteville terrace/Bartels road. This data includes turn volumes and annual average daily traffic (AADT) of the intersections, AADT of Wakefield road and predicted speed and queue times for vehicles up to 2011. Based on the interpretation of this data we can make a definite conclusion of what road needs to be investigated for the newly developed roundabout.

Britannia Corner Intersection (Pre-2013)

Peak Times

Table 1 illustrates the peak times for approaching and departing traffic based on historical data collected in 1998.

Table 1-Traffic Movements IN and OUT for AM and PM peak hour times, Showers, 1998 - Appendix C

INTO AM OUT AM INTO PM OUT PM

Fullarton South – 2164 Fullarton South – 1274 Fullarton South – 1582 Fullarton South – 1238

Fullarton North – 767 Fullarton North – 619 Fullarton North- 619 Fullarton North – 754

Kensington – 695 Kensington - 441 Kensington – 553 Kensington – 842

Dequetteville – 755 Dequetteville – 1011 Dequetteville – 676 Dequetteville – 794

Wakefield – 466 Wakefield – 1441 Wakefield – 721 Wakefield - 523

Table 1 above displays the traffic counts of the intersections of the Britannia roundabout prior to its redevelopment. The traffic count for the AM peak for the vehicles that are arriving into Fullarton Rd South have a total volume of 2, 164 veh/hr and for the vehicles which are leaving onto Wakefield Rd have a total volume of 1,441 veh/hr.

The PM peak for both arriving and departing traffic via Fullarton Rd South was approximately about 1,582 veh/hr and 1,238 veh/hr respectively. Therefore, this points out that the traffic volume is slightly greater during AM peak times compared to PM peak times for this instance.

Thus, Fullarton Rd South and Wakefield Rd are the two major arterial roads that suffer the most during both AM and PM peak.

Table 2-Traffic Movements IN and OUT for AM and PM peak hour times, Dry Conditions, 2002 - Appendix A

INTO AM OUT AM INTO PM OUT PMFlinders Street- 1263 Flinders Street- 630 Flinders Street- 523 Flinders Street- 1217Dequetteville South- 1248

Dequetteville South- 852

Dequetteville South-960

Dequetteville South- 1055

Bartels Road- 971 Bartels Road- 1937 Bartels Road- 2043 Bartels Road- 938Dequetteville North- 1190

Dequetteville North- 1246

Dequetteville North- 969

Dequetteville North- 1277

Table 2 above illustrates the peak times for approaching and departing traffic based on historical data collected in 2002 for the intersection of Dequetteville Tce/Bartels Rd/Flinders Street. The traffic count for the AM peak for the vehicles that are approaching into Flinders Street have a total volume of 1,263 veh/hr and for the vehicles which are departing onto Bartels Rd have a total volume of 1,937 veh/hr.

The PM peak for the vehicles arriving into Bartels Rd have a total volume of 2,043 veh/hr and for the vehicles which are departing onto Dequetteville North have a total volume of 1,277 veh/hr. Therefore, this proves that the traffic volume is slightly greater during PM peak compared to AM peak times. Hence, Flinders St, Bartels Rd and Dequetteville North are all a factor of major arterial road which suffers the most during both AM and PM peak.

Table 3-Traffic Movements IN and OUT for AM and PM peak hour times, Dry Conditions, 2002 - Appendix B

INTO AM OUT AM INTO PM OUT PMFullarton South- 1496 Fullarton South- 1185 Fullarton South- 1213 Fullarton South- 1360

Greenhill West- 1871 Greenhill West- 1004 Greenhill West- 1109 Greenhill West- 2029

Fullarton North-1899 Fullarton North- 2453 Fullarton North- 2276 Fullarton North- 1881

Greenhill East-1243 Greenhill East-1879 Greenhill East-2459 Greenhill East-1534

Table 3 above illustrates the peak times for approaching and departing traffic based on historical data collected in 2002 for the intersection of Fullarton Rd/Greenhill Rd. The traffic count for the AM peak for the vehicles that are approaching into Fullarton North have a total volume of 1,899 veh/hr and for the vehicles which are departing onto Wakefield Rd have total volume of 2,453 veh/hr.

The PM peak for the vehicles arriving into Greenhill East have a total volume of 2,459 veh/hr and for the vehicles which are departing onto Greenhill West have a total volume of 2,029 veh/hr. Therefore, this proves that the traffic volume is slightly greater during PM peak times compared to AM peak times as there is more traffic flow during PM peak hours for the intersection of Fullarton Rd/Greenhill Rd. For this situation, Fullarton North Rd and Greenhill Rd are the two major arterial roads which suffer the most during peak hour times.

When observing all the intersections, it is essential to state what is occurring during the peak hours which make the traffic volumes quite high on these roads. From Table 1 it is possible to see that the major turning movement during the AM peak is onto Wakefield Rd, which suggests that the traffic used Wakefield Rd as an access into the Adelaide City particular from the Southern/Eastern metropolitan areas, via Fullarton Rd South. It is evident that Fullarton Rd South is the busiest arm of the intersection during AM peak, as it having three or more times of the amount of traffic volume. However, during the PM peak the motorists are accumulating twice as much traffic at Fullarton Rd South compared to any arm in the intersection when departing during PM peak.

From Table 2 it is possible to see that the major turning movement during the AM peak is onto Bartels Rd, which suggests that the traffic used Bartels Rd as an access into the city particular from the Southern/Eastern metropolitan areas, via Flinders Street. It is also relevant to state the motorists travelling from Dequetteville Terrace for both South and North directions have a high turning movement onto Bartels Rd. However, during the PM peak majority of the motorists are approaching the city through Bartels Rd and then departing through Dequetteville North. However, it can be said that the traffic volume is relatively evenly spread when departing from Bartels Rd during PM peak.

From Table 3 it is possible to see that the major turning movement during the AM peak is onto Fullarton Rd North, which suggests that the traffic used Fullarton Rd North as an access into the city, via Fullarton Rd North. It is obvious that Fullarton Rd North is the busiest arm of the intersection during AM peak. However, during the PM peak majority of the motorists are approaching the city through Greenhill East and then departing through Greenhill West.

Average Annual Daily Traffic

Table 4-The Average Annual Daily Traffic (AADT), Appendix A

Arm of Intersection Estimated AADT

Flinders Street 17700

Dequetteville South 21700

Bartels Road 27700Dequetteville North 23900

Table 5-The Average Annual Daily Traffic (AADT), Appendix B

Arm of Intersection Estimated AADTFullarton South 28400Greenhill West 30600Fullarton North 44100Greenhill East 37300

Table 6-The Average Annual Daily Traffic (AADT), Appendix C

Arm of Intersection Estimated AADTFullarton South 34800Fullarton North 16000Kensington 15000Dequetteville 18500Wakefield 16400

To ensure that all the historical data has been considered, AADT can be used as a secondary option to find out which major arterial road suffers the most during peak times. Annual average daily traffic (AADT) is a measure used primarily in transportation engineering. Usually, it is the total volume of vehicle traffic of a highway or road for a year divided by 365 days.

The greatest estimated AADT was 27700 vehicles per day at Bartels Rd for the intersection of Dequetteville Tce/Bartels Rd/Flinders Street. Refer to Table 4 for all other data.

The greatest estimated AADT was 44100 vehicles per day at Fullarton North for the intersection of Fullarton Rd/Greenhill Rd. Refer to Table 5 for all other data.

The greatest estimated AADT was 34800 vehicles per day at Fullarton South for the intersections of the Britannia roundabout. Refer to Table 6 for all other data.

From the department of transports turning movement survey on the Britannia roundabout and surrounding intersections, the trends of the traffic movement can be figured out.Firstly examining the Britannia roundabout, there are five different arms to this intersection,

Fullarton Road north, Kensington Road, Fullarton Road south, Wakefield Road and Dequetteville Terrace.When looking at the 11 hour totals for each of the individual roads, it is possible to see where most motorists are approaching from and where they are subsequently turning out of the roundabout from the respective road.

Table7: Traffic Movements 11 Hour Totals Each Arm of Intersection (Britannia Roundabout)

Fullarton (N) Kensington Fullarton (S) Wakefield DequettevilleFullarton (N) 0 271 4230 925 102Kensington 127 0 1504 2456 1389Fullarton (S) 4904 1250 0 3106 5443Wakefield 1215 2586 1179 0 756Dequetteville 188 1597 4363 4 0

From Table 7 it is evident that Fullarton Road (south) is by far the busiest arm of the intersection, with it accumulating twice as much traffic as any other arm in the intersection, therefore making this arm most susceptible to delays and long queues. Also when looking at the peak flows for the mornings and afternoons, the traffic flow is similar with Fullarton Road (south) again being the arm with the most traffic (See Appendix C).

Table 8: Traffic Movements 11 Hour Totals Each Arm of Intersection (Dequetteville Tce/Bartels Rd/Flinders St)

Flinders Dequettevile (S) Bartels Dequettevile (N)Flinders 0 145 6050 0Dequettevile (S) 234 0 7148 1443Bartels 6658 1689 0 2600Dequettevile (N) 222 5654 2365 0

From Table 8 the traffic flow at this intersection (Appendix A) suggests that majority of the vehicles try and avoid heading to the Britannia roundabout (Dequetteville Terrace south), around a third of the vehicles travelling along Dequetteville Terrace (north), turn right onto Bartels Road rather than continuing straight towards the Britannia roundabout.

Figure 2 Fullarton Rd/Bartels Rd/Flinders St Intersection

Table 9: Traffic Movements 11 Hour Totals Each Arm of Intersection (Fullarton Rd/Greenhill Rd)

Fullarton (N) Greenhill (E) Fullarton (S) Greenhill (W)Fullarton (N) 0 1656 8648 6212Greenhill (E) 2926 0 1556 7482Fullarton (S) 8804 1883 0 668Greenhill (W) 5926 8207 458 0

When examining Table 9, Fullarton Road (north) is the arm that continues towards the Britannia roundabout. Majority of the vehicles entering Fullarton Road (north) and continuing towards the Britannia roundabout are from either Fullarton Road (south) or Greenhill Road (west). When comparing this intersection to the Britannia roundabout it is seen that the transit times would be more preferable at the roundabout, as the total number of vehicles in the 11 hour interval for the Britannia roundabout is much less than the Fullarton Road/Greenhill Rd intersection, 37595 vehicles and 54426 vehicles, respectively. Therefore having a lower number of vehicles means lower queueing times and less delays, creating a more favourable transit time.

Figure 3 Fullarton Rd/Greenhill Rd Intersection

Queuing and Mean SpeedThe data from 1998, gave a predicted 1999 mean vehicle delay of 236 seconds for AM and 220 seconds for PM, for the conditions of a roundabout, see Figure 6. However the predicted 2011 mean vehicle delay was 535 seconds for AM and 520 seconds for PM, again for the conditions of a roundabout. This suggests that the traffic flow would be a lot heavier and the queueing a lot longer. This therefore directly correlates to the mean speed of the vehicles, as mean vehicle delay increases, the mean vehicle speed decreases. This can be seen in Figure 7, as the predicted 1999 mean speed is 18.6 kph for AM and 20.3 kph for PM, and for the predicted 2011 mean speed is 7.4 kph for AM and 7.5 kph for PM, these are again both under the conditions of a roundabout.

Figure 6 Graphs of Predicted Mean Vehicle Delay Figure 7 Graphs of Predicted Mean Speed

Location of Traffic Count on Fullarton Road

Figure 8: Location of Fullarton road Traffic Count

Britannia Roundabout Intersection (Post-2013)

To perform an analysis on the new development, we need to examine a major arterial road by performing our own traffic count; therefore in order to perform an accurate analysis, the AM and PM peak movements will be counted.

By analysing the one way traffic count during peak times for roads that suffers from high traffic volumes, we can obtain data queue lengths and peak traffic volumes.

As previously mentioned Fullarton rd (South) and Wakefield rd suffer high volumes of traffic, during AM and PM peak (Table 1). Table 10, like Table 1 illustrates the peak times for approaching and departing traffic based on historical data collected in 1998. Therefore when conducting our traffic count, it will be performed in 2015 under the assumption that Fullarton rd (South) and Wakefield rd will still be the main roads of focus due to their historically high traffic volume.

Table 10: Traffic Movements IN and OUT for AM and PM peak times, 1998 - Appendix C

INTO AM OUT AM INTO PM OUT PMFullarton South – 2164, 8am

Wakefield – 1441, 8am Fullarton South – 1582, 5pm

Fullarton South – 1238, 5pm

Fullarton North – 767 Fullarton South – 1274 Wakefield – 721 Kensington – 842Dequetteville – 755 Dequetteville – 1011 Dequetteville – 676 Dequetteville – 794Kensington – 695 Fullarton North – 619 Fullarton North 619 Fullarton North – 754Wakefield – 466 Kensington - 441 Kensington – 553 Wakefield - 523

Location of Traffic Count on Wakefield Road

The locations of the traffic counts are in figure 8 and 9 for Wakefield road and Fullarton rd south respectively.

Table 11 shows the traffic count yields a result for AM peak, a volume of 2,448 veh/hr approaching Fullarton rd south, for the vehicles departing onto Wakefield rd a volume of 1,664 veh/hr was recorded.

The PM peak for both approaching and departing traffic via Fullarton rd south was 1,717 veh/hr and 1,559 veh/hr respectively. Obviously this highlights that the traffic volume is particularly heavy during AM peak times. The traffic growth shows no steady increase over the past 13 years which highlights there is no annual increase of 2% on the newly developed roundabout.

27/5/15 Traffic CountINTO AM OUT AM INTO PM OUT PM

Fullarton South – 2448

8-9am

Wakefield rd – 1664, 8-9am

Fullarton South – 1717, 5-6pm

Fullarton South – 1559, 5-6pm

Traffic Growth Increase

13.1% 15.4% 8.5% 25.9%

Table 11: Traffic Movements IN and OUT for PM peak times, Traffic Count 27/5/15

Figure 9: Location of Wakefield rd Traffic Count

Queuing

“The behaviour of a queuing system, as reflected in queue lengths and delays, may vary over an analysis period for one of two reasons:

1. Both rates remain constant over the analysis period but the average arrival rate equals or exceeds the average service rate (i.e. the utilisation factor, ρ, is greater than or equal to one)”

2. Over the period, there is variation in the average arrival rate and/or the average service rate.

(Guide to traffic management, Traffic theory: Part 2)

Case 1 is known as steady state queuing, for the purposes of the project we will only be referring to dynamic queuing as the analysis is conducted during peak times.

Case 2 is known as dynamic queuing, this means that the queue lengths and times may differ across the peak period. Dynamic queuing is important as it allows the analyst to find maximum queue lengths and delays that occur as sometimes the maximum queue lengths and delay may exceed the service rates of the approach. This case most likely applies to the Britannia roundabout due to the following reasons.

1) During the PM peak time, Fullarton rd suffered queues in only one of the two lanes, the left lane for traffic travelling onto Wakefield rd and Dequetteville terrace was free flowing with particularly minimal delays. However for traffic turning right onto Fullarton rd north or Kensington rd, there flow of traffic was halted several times.

2) During peak times the movement of traffic for the AM period is favourable in the direction of North-South and East-West movements, during the PM peak period this is reversed.

Based on data from 1998 48.9% of vehicles approaching Britannia roundabout from Fullarton rd South, perform a right turn onto Kensington and Fullarton rd North. If we apply the same value to the volume from the traffic count, 839 vehicles performed a movement onto Kensington and Fullarton rd north during the PM peak times.Again based on historical data 42% of vehicles turned onto Wakefield rd from Fullarton road during peak AM peak times, applying the same value to the traffic count, 699 vehicles perform a movement onto Wakefield road during AM peak times.

Referring to figures 10 and 11, the queue length in the right and left lane of Fullarton rd South during the PM peak time spanned 244m and 321 respectively, if a length of 6m is allowed between headways of vehicles then the number of vehicles queued on Fullarton road are approximately 41 and 54 respectively.Another investigation that was performed was the mean delay of vehicles, this reference the time it takes for a vehicle to complete a turn movement while impeded by circumstances that stop free flow of traffic. Refer to table 12

Mean Delay AM peak, Fullarton Road (South) Mean Delay PM peak, Fullarton Road (South)90 seconds 108 seconds

Table 12: Mean Vehicle Delay times AM and PM peak

Figure 10: Queue length for right lane on Fullarton rd PM peak Figure 11: Queue Length for left lane on Fullarton road AM peak

Comparison

The data from above has been interpreted, but what sort of conclusion can we draw from them. Can the new intersection actually be an upgrade on the previous design? We need to discuss what has actually improved at this roundabout or if some of the underlying issues still remain.

SafetyAccording to the Department of Transport and Infrastructure the development of the new roundabout will reduce total road crashes by up to 29% and reduce casualty crashes by up to 23%.

“The majority of crashes occur at the Wakefield Road / Dequetteville Terrace junction and at Kensington Road approach. The improvements to the Britannia roundabout will reduce the number of crashes at this intersection, particularly at these two locations. The improvements will reduce the incidence of right-angle, rear-end and side-swipe crashes.” – DPTI

Unfortunately there is no available statistics for obtaining crash history that does not involve a major collision or fatality. As Britannia roundabout is a very free flowing, low speed intersection the probability of major collisions that cause severe damage is very low.

According to the most recent article by 7news from March 15 2014, since the introduction of the new Britannia roundabout the RAA stated that the numbers of collisions have been reduced by 33%. The dual roundabout design has, apparently in 6months of operation, caused 14 collisions; when compared to the two and a half years before the new development there were 172 reported accidents at the intersection (7news.com.au).

From these statements it certainly shows that there is a significant reduction in traffic incidents from the redevelopment. Unfortunately as these are only statements and no proper statistics/data have been released, a distinct conclusion cannot be drawn.

Queue Delay

“An improvement in afternoon peak efficiency is expected. The current intersection takes an average of 78 seconds to travel through in the afternoon peak. It will take an average of 38 seconds to travel through the upgraded intersection in the afternoon peak period. This project maintains the existing level of service in terms of efficiency in the morning peak. There is a 10%-15% increase in efficiency in the afternoon peak” – DPTI, Fast Facts Britannia Roundabout

As the historical data is based on all turning movements, the mean delay may be quite different for only Fullarton rd and Wakefield rd.Based on historical data from 1998, the mean vehicle delay during peak A.M and P.M times were 236 and 220 seconds respectively. For AM and PM peak the mean vehicle delay that occurred on Fullarton road was 90 and 108 seconds. When comparing this with figure 2 it shows that for this turning movement there is a significant decrease by around 2 and a half minutes in vehicle delay. The delay on Fullarton road during AM peak times can be explained by the high West- East

movement of traffic from Kensington road to Wakefield road. Unless there was ways to ignore the movement from East-West like a tunnel, delay will inevitably occur on Fullarton rd (South). During AM peak, further analysis could be made to find if a bottleneck is occurring at Wakefield rd and whether the road is at its capacity for this time period, Wakefield rd still maintains two lanes for one way traffic, maybe an investigation into whether this is suitable for future use should be performed as this could potentially reduce vehicle delays on Fullarton rd.

It came as a surprise that for PM peak times the vehicles delay was higher than the AM vehicle delay, however this time can be clarified by the high North-South movements occurring at this time. However if a lot of the turn movements are moving onto Fullarton rd then why could the right lane from the opposite direction be delayed. From Google Maps, it appears that there is only 29 metres of separation between three possible turning movements. Kensington rd, and both the entrance and exits for Fullarton road (South) have such a small distance between them that it is quite possible, that there is hesitation with the drivers in the right lane on Fullarton road. There still appears to be a lack of trust in the Britannia roundabout, drivers are still hesitant to complete a turn due to the reputation that Britannia roundabout is one if the worst intersections in Adelaide.

Like road safety it certainly highlights that Britannia roundabouts redevelopment has been for the better in terms of vehicle movement and delay. It has been possible to reduce vehicle delays but unfortunately we can’t change driver’s habits.

Conclusion

The aim of this project was to analyse and interpret the historical data that had been provided by DPTI for Britannia roundabout; from this analysis Fullarton rd (South) and Wakefield Rd suffered the highest volumes of traffic in AM and PM peak periods. At nearby intersections, Bartels rd continues to be a busy intersection, with movements to Dequetteville terrace still the major movement at PM peak periods. During the AM and PM periods, Fullarton rd maintains a strong North to South movement while Greenhill Rd maintains a its West-East movements during AM and PM peaks, this suggests that Greenhill Rd is still preferable for East-West movements rather than turning movements East-West on Britannia Roundabout via Fullarton road.

A traffic count was performed on Fullarton rd and Wakefield rd; this was in order to compare some of the trends that the historical data showed. Data showed there was significant growth in the traffic volume with the new development of the roundabout; there was no consistent growth which showed that there was a steady increase in traffic volume at Fullarton rd and Wakefield rd. This highlighted that Britannia roundabout is very dynamic in terms of growth, as some drivers would prefer not to use the roundabout due to its reputation.

When comparing the 2015 data with the historical data, there appeared to be significant improvements in relation to the new developments safety and queuing data. DPTI expectations were not only met, but exceeded their initial projections of improvement in traffic quality at this intersection.

It appears that the redevelopment of the Britannia roundabout has certainly improved its reputation as being one of the worst intersections in Adelaide. Drivers are still apprehensive about still negotiating this busy intersection since its redevelopment, however with improvements to queuing times and road safety it is steadily becoming a reputable improvement in Adelaide.

References

Erceg, J., Brown, S., Bennett, D., Troutbeck, R., Croft, P., McTiernan, D. and Sha, A. (n.d.). Guide to traffic management.

Au.news.yahoo.com, (2015). Figures show fewer crashes at dual Britannia Roundabout. [online] Available at: https://au.news.yahoo.com/sa/a/23892414/figures-show-fewer-crashes-at-dual-britannia-roundabout/ [Accessed 25 May. 2015].

Infrastructure.sa.gov.au, (2015). DPTI - Department of Planning, Transport and Infrastructure South Australia - Fast facts. [online] Available at: http://www.infrastructure.sa.gov.au/content/britannia/fast_facts [Accessed 25 May 2015].

Appendix A

Appendix B

Appendix C