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Contents
A43 Silverstone Bypass - Traffic Impact Study Report
Executive summary
The A43 (T) Silverstone Bypass officially opened on the 18th September 2002, providing an improved route for through traffic using the A43 between Brackley and Towcester, Northamptonshire, as illustrated in the diagram below. The scheme provides a continuous dual carriageway between the M40 and A5. It comprises two sections of new dual carriageway, bypassing the villages of Silverstone and Syresham, as well as widening of all single carriageway sections. "Before" and "After" traffic data for the bypass was collected immediately prior to and after scheme opening in September to monitor the effects of the new scheme. In addition, traffic data from surveys on County roads from Northamptonshire County Council and existing Highways Agency permanent count sites was obtained to evaluate the effects of the opening of the A43 (T) Silverstone Bypass on strategic traffic routeing patterns in the area.
Figure 0.1 - Daily Traffic Flows "Before" and "After" Scheme Opening
The main effects of scheme opening are as follows:
- Daily traffic flows rose from around 28,000 vehicles per day before opening to 30,000 vehicles on A43 (T) Syresham Bypass during the first two weeks of the scheme's official opening, thus an additional 2,000 vehicles have been drawn into the corridor;
- Traffic on the main road in Silverstone dropped from 27,000 to 2,600 vehicles per day (a 90% reduction), while traffic in Syresham village was only 490 vehicles following scheme opening in September, representing a 98% decrease;
- Traffic flows on a County B-road, the B4525 (linking with the A43 (T) Syresham Bypass), have increased by 800 vehicles per day, representing a 30% increase;
- A redistribution of traffic from other routes in the area to the A43 (T) appears to have
- taken place to take advantage of scheme improvements to the A43 strategic route;
- There were traffic flow reductions observed on the A361, A422 and A413 routes in Northamptonshire, which totalled around 1,300 vehicles; and
- Journey time savings of up to 10 minutes are forecast for movements that previously used the old A43 route through the villages of Silverstone and Syresham.
1. Introduction
1.1 This report outlines the results of traffic surveys carried out to monitor the effects of the recently opened A43 (T) Silverstone Bypass. The scheme provides an improved route for through traffic using the A43 between Brackley and Towcester, in Northamptonshire. It forms part of the M40 - A5 Dualling Scheme, providing a continuous dual carriageway between the M40 and A5. The A43 (T) Silverstone scheme replaces the old single carriageway road and comprises two bypass sections around the villages of Silverstone and Syresham, as illustrated in Figure 1.1.
1.2 The A43 (T) Silverstone Bypass was officially opened on the 18th September 2002, although was opened as a single carriageway in early September. The scheme was partially open in July 2002 for the British Grand Prix as part of the network traffic management plan routeing spectator traffic to and from the race circuit. "Before" and "After" traffic data for the bypass was collected immediately prior to and after the September opening date in order to prepare a Traffic Impact Study (TIS) on the effects of the scheme opening. In addition, traffic data from Northamptonshire County and Highways Agency count sites has been used to evaluate the effects of the opening of the A43 (T) Silverstone Bypass on strategic traffic routeing patterns in the area.
1.3 Chapter 2 of this report discusses the data collected as part of the TIS study. Chapters 3 and 4 summarise the main results and conclusions.
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Figure 1.1 - Location of A43 (T) Silverstone and Syresham Bypass Sections
2. Data Collected
2.1 The Traffic Impact Study (TIS) for the A43 (T) M40 to A5 Dualling included the following surveys:
"Before" Surveys
- 2 Automatic Traffic Count surveys by Count-On-Us. As the scheme opened a little early, traffic counts from June 2001 were used to represent traffic volumes in the "Before" situation;
- 4 ATC surveys by Atkins on behalf of Northamptonshire County Council;
- Traffic data from 4 Highways Agency permanent count site locations; and
- Journey time surveys on A43 (T) from M40 to the A5 at Towcester.
"After" Surveys
- For the "After" surveys, the above surveys were used, plus two additional ATC surveys on the new A43 bypass sections.
2.2 The details of the "Before" and "After" surveys are described below.
Automatic Traffic Counts.
2.3 Atkins undertook automatic traffic count (ATC) surveys in September 2002 at the following four locations, as illustrated in Figure 2.1:
- Old A43 Brackley Road (Silverstone village);
- Old A43 Main Road (north of Syresham village);
- New A43 Silverstone Bypass (south of A413 junction); and
- New A43 Whitfield Turn to Brackley Hatch Dualling (Green Man junction).
2.4 The scheme itself was due to open on 18th September 2002, and thus, the count equipment was connected on Thursday 12th September and continued for five weeks to incorporate the scheme opening day and the weeks after opening.
2.5 Traffic data from surveys undertaken by Atkins on behalf of Northamptonshire County Council to monitor the effects of the scheme opening on other routes in Northamptonshire and data from permanent Highways Agency count sites has also been obtained to ensure a comprehensive evaluation of any strategic traffic routeing changes in Northamptonshire.
2.6 The County sites are as follows (and illustrated in Figure 2.1):
- B4525 at Falcut (alternative to A422 from J11 of M40 (Banbury));
- A361 at Byfield (route from J11 of M40 to Daventry);
- A422 at Deanshanger (route from Buckingham joining A5 west of Milton Keynes); and
- A413 at Lillingstone Dayrell (route from Buckingham to A43 south of Towcester).
2.7 Traffic data has been obtained from Highways Agency permanent count sites on trunk roads (as shown in Figure 2.1), namely;
- A43 at Whitfield (south west of scheme);
- A43 at Blisworth (north east of Towcester); and
- Two locations on the A5 at Pattishall and Alderton (north and south east of Towcester).
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Figure 2.1 - Location of Traffic Count Sites
Journey Time Surveys
2.8 Journey time surveys were undertaken on the A43 (T) between the junction 10 of the M40 and A5 at Towcester. The surveys covered the full A43 (T) M40 - A5 Dualling Scheme, which includes the M40 to B4031 (A421) improvement (dualling of existing single carriageway road) which was completed in February 2002. The survey route, comprising five timing points, is depicted in Figure 2.2.
2.9 "Before" journey time surveys previously undertaken in June 2001 were used for comparison with surveys carried out post scheme opening. Survey periods were the morning (07:30 - 09:00) and evening (16:30 - 18:00) peaks as well as an inter-peak period (10:00 -11:30).
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Figure 2.2 - Journey Time Survey Route from M40 to A5
3. Summary of Results
3.1 Figure 3.1 below summarises the "Before" and "After" ATC information using five day average two-way traffic flows. A summary results table is included in Annex A of this report.
Figure 3.1 - "Before" & "After" ATC Results: 5 Day Average
3.2 Figure 3.1 shows the 24 hour two way traffic flow on the new bypass for an average weekday in September. Following scheme opening on 18th September 2002, around 28,000 - 30,000 vehicles were recorded using the new bypasses at Silverstone and Syresham respectively. This represents a 2,000 increase in the traffic volumes recorded prior to the scheme opening. Traffic volumes are slightly higher (29,800 vehicles) on the section of carriageway bypassing Syresham (Whitfield Turn to Brackley Hatch) compared with Silverstone Bypass (28,000 vehicles).
3.3 Very low traffic volumes (2,630 and 490 vehicles per day) were observed in Silverstone and Syresham respectively in the latter part of September indicating the scheme has been successful in routeing traffic (over 24,000 vehicles) away from the villages.
3.4 Traffic volumes from the Highways Agency permanent count sites on the A43 (T) at Whitfield to the south west of the scheme and Blisworth to the north east of Towcester (refer to Figure 2.1) also demonstrate an increase of 3,000 vehicles in the A43 corridor.
3.5 Daily traffic volumes on the A43 at Whitfield increased by some 3,000 vehicles to 27,700 vehicles per day after scheme opening (13% increase), matched by a 3,000 increase to 34,100 vehicles at Blisworth (a 9% increase). Furthermore, daily traffic levels increased by around 500 vehicles at both Highways Agency sites on the A5 route.
3.6 Additional traffic has also been recorded on the B4524, a parallel route to the A422 from the M40. The daily flow increased by around 800 vehicles per day following scheme opening, which represents a 30% increase.
3.7 From examination of County data, it is evident that traffic levels have decreased on certain roads in the Northamptonshire area. For example:
- There has been a reduction of 570 vehicles per day on the A361 route (parallel to the A43 from junction 11 of the M40 to Daventry);
- There are 600 fewer vehicles on the A422 route (a parallel route from Buckingham to the A5 at Milton Keynes);
- There is a reduction of 150 vehicles per day on the A413 (route from Buckingham joining the A43 to the north east of the scheme and south of Towcester); and
- In total, therefore a reduction of 1,300 vehicles per day has been observed on the parallel roads.
Journey Times
3.8 A summary of the journey times from the "Before" and "After" scheme opening surveys is shown in the table below.
3.9 This table clearly indicates that significant time savings are being observed on the A43 between the junction 10 of the M40 and A5 at Towcester. These savings are around 7 minutes in the northbound direction and up to 10 minutes in the southbound direction, which represents an increase in speeds from around 40kph in all time periods to around 60kph after the road was opened.
| Direction | Period | Journey Time | ||
|---|---|---|---|---|
| Before | After | Saving | ||
| Northbound | AM | 26:18 | 18:38 | 07:40 |
| Inter | 25:25 | 17:44 | 07:43 | |
| PM | 28:53 | 20:57 | 07:56 | |
| Southbound | AM | 29:07 | 18:37 | 10:30 |
| Inter | 26:25 | 17:44 | 08:41 | |
| PM | 28:45 | 19:27 | 09:18 | |
Discussion of Results
3.10 The results from traffic counts on the A43 (T) suggest that there has been a redistribution of traffic on roads in the Northamptonshire area following opening of the new bypass and scheme improvements on the A43. An additional 2,000 - 3,000 vehicles have been attracted into the A43 (T) corridor. Around half of these (1,300 vehicles) appear to have been drawn from other County A-roads, evidenced by a decrease in traffic flows on the A361, A422 and A413.
3.11 Whilst it has not been possible to track changes in flow across all possible routes, it is expected that the remainder is a result of a reassignment of long distance traffic. Given the strategic nature of the widening of A43 and the opportunity that the scheme presents for movement between the M1 and M40, some vehicles may potentially re-route onto the A43 from routes such as M42, A46 and even M25.
3.12 This additional traffic drawn into the corridor only equates to around 5% of the daily traffic using the A43, therefore the level of induced traffic (new trip generation) is likely to be minimal.
3.13 Interestingly, the results show a 30% increase in traffic levels on a County B-road, the B4524, following bypass opening. Clearly, the scheme has encouraged a redistribution of trips onto this road, related to improved links to the A43 (T) following construction of a new grade separated junction on the section of bypass around Syresham.
3.14 Traffic volumes observed on the old A43 Brackley Road through Silverstone showed a significant decline, although traffic volumes of 2,630 vehicles per day were observed following scheme opening. As there is no turn onto the A413 south from the northbound A43, it is possible that vehicles are routing via Silverstone to access the A413 southbound.
4. Conclusion
4.1 The traffic data collected as part of this Traffic Impact Study demonstrates that the new A43 (T) Silverstone Bypass, which officially opened on 18th September 2002, carries around 28,000 - 30,000 vehicles per day (on an average weekday). Traffic count data, post scheme opening in September, shows very low traffic volumes in Silverstone and Syresham, clearly indicating that the scheme has been successful in routeing over 24,000 vehicles away from these villages.
4.2 It is apparent that the A43 (T) scheme has drawn additional traffic into the corridor, mainly from parallel routes in Northamptonshire to take advantage of time savings on the improved A43 route between the M40 and A5 at Towcester. The results of traffic surveys suggest that this additional traffic volume is some 2 - 3,000 vehicles per day (based on September 2002 data).
4.3 Traffic flows on a County B-road, the B4524, have also shown a significant increase following scheme opening of 800 vehicles per day, which represents a 30% increase in daily traffic. This is most likely related to improved links for traffic using the B4525 joining the A43 (T) at Syresham, following construction of a grade separated junction, as part of the highway scheme.
4.4 A reduction of traffic on three A-roads routes in Northamptonshire has been observed following scheme opening, for example a decrease of 570 vehicles was shown on the A361, a decrease of 600 vehicles per day on the A422 and a reduction of 150 vehicles on the A413. This represents around half (1,300 vehicles) of the additional traffic using the A43 (T) route, the remainder of which is expected to be as a result of changes to long distance movements re-routeing from other strategic motorway and trunk road routes.
4.5 Journey time data suggests that time savings of up to 10 minutes are being forecast for journeys along the A43 following scheme improvements to the trunk road.
4.6 The One Year "After" Count for this scheme's Post Opening Project Evaluation will be undertaken in September 2003.