6 Traffic and Economic Assessment 6.1 Traffic Modelling 6.2 Forecasting 6.3 Predicted Traffic Flows 6.4 Economic Performance of Options
6 Traffic and Economic Assessment
6.1 Traffic Modelling
A traffic model has been constructed using 2005 survey data (see Section 2.3) and the NESA37 software program, as documented in report "Local Model Validation and Forecasting Report", dated September 2006.
The model area follows the length of the A90 corridor between Blackdog, north of Aberdeen to the A90, south of Ellon. It also includes an area to the east of the A90 comprising of the A975 and the B9000 which link through Newburgh and the main roads that make up the local network in Balmedie. The traffic data entered in the model are 12 hour survey information that was recorded in November 2005.
An excel spreadsheet has been used to set up the origin and destination trips between zones. This is based on the registration number survey that determined the element of through traffic, the manual classified turning counts and the 2001 census data to determine an estimate of the distribution of traffic between zones.
The main side roads onto the A90 have been modelled where the levels of traffic flows are significant or an access provides a significant entrance into certain areas, all the junctions operate as priority junctions. The side roads have been modelled in NESA in order to account for the accident benefits associated with reducing the volume of traffic passing these junctions as a consequence of the new off-line dual carriageway.
The 12 hour flows on the existing route in 2005 are shown in Figure 2.3.
6.2 Forecasting
The base matrix was developed for 2005, 2010 and 2020. Traffic forecasts have been prepared using central National Road Traffic Forecasts (NRTF) growth factors together with the specific traffic generated by proposed developments to the south of Balmedie. Additional flows were generated for the proposed developments set out in the local plan using the TRICS database. The development traffic was added to the matrix in 2010 and the traffic was distributed onto the network in a similar pattern to the other Balmedie zones.
The B977 to the west of Balmedie currently provides an alternate route to the congested A90 Anderson Drive for accessing Dyce and Aberdeen Airport. The Aberdeen Western Peripheral Route (AWPR) is expected to be complete in 2011. The AWPR reduces the traffic to the east of the B977 (zone 8) by 3,400 vehicles (4,500 to the west of B977 – 1,100 on the B999) and increases the traffic on the A90 (Zone 1 and 21) by 1,600 vehicles at the year of opening. This effect has been taken into account in constructing the 2020 matrix.
6.3 Predicted Traffic Flows
The predicted traffic flows for each sub-option are shown in Figures 6.1 - 6.4. As can be seen there is no significant difference in flows between each sub-option with the majority of traffic transferring onto the new dual carriageway. The average journey time saving in the 2010 opening year is 1 minute 30 seconds during the peak period.
In terms of accidents, the following savings are predicted over 60 years:
Casualties |
Fatal |
Serious |
Slight |
|---|---|---|---|
Base Scheme |
45 |
251 |
1631 |
Design Scheme |
21 |
149 |
1483 |
Reduction |
24 |
102 |
148 |
Table 6.1: Predicted Accident Reductions
6.4 Economic Performance of Options
The four route sub-options have been assessed for economic performance using the NESA Model. A ‘Stage 2: Traffic and Economic Report’ has been prepared to document the NESA results, a summary of these can be seen in Table 6.2 below.
Sub-option 1 |
Sub-option 2 |
Sub-option 3 |
Sub-option 5 |
|
|---|---|---|---|---|
Present Value Costs |
44.26 |
44.01 |
44.21 |
40.76 |
TIME - Link Transit |
99.02 |
101.84 |
101.88 |
98.57 |
Time - Junction Delay |
3.90 |
3.87 |
3.87 |
3.58 |
Vehicle operating costs |
-8.88 |
-7.43 |
-7.22 |
-8.47 |
Accidents - Links |
27.98 |
28.28 |
28.32 |
27.85 |
Accidents - Junctions |
1.66 |
1.65 |
1.65 |
0.51 |
Present Value Benefits |
123.67 |
128.22 |
128.50 |
122.04 |
Net Present Value |
79.40 |
84.21 |
84.29 |
81.28 |
BCR |
2.79 |
2.91 |
2.91 |
2.99 |
Table 6.2: Economic Evaluation Results
All sub-options have substantial time-saving benefits generated over the 60 year evaluation period. Sub-option 5 has slightly less time benefit due to the location of the A975 junction being further west than the other sub-options. All sub-options perform well in terms of value for money indicators having BCRs between 2.79 and 2.99. A value of this level represents good value for money. In comparative terms, the main factor is that although Sub-option 5 is substantially cheaper that does not result in a significant drop in economic performance when compared with the other sub-options.