Highways Agency

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A11 roudham heath - attleborough improvements

A11 Roudham Heath - Attleborough Improvements

Executive Summary

The A11 Roudham Heath to Attleborough Improvements scheme opened on the 19th March 2003. The road is a part of the core National Route linking London, Cambridge and the northern part of East Anglia. This section is one of the remaining single carriageway sections on this strategic route. The improvements included adding a second carriageway, building a new dual carriageway and various other improvements. This scheme, together with two other improvement schemes, will complete the dualling of the A11 between the M11 and Norwich Southern Bypass (A47). The other two schemes, the A11 Attleborough Bypass Improvement and the A11 Fiveways to Thetford Improvement, are scheduled to begin construction in 2005 and finish in late 2007.

The principle objectives of the scheme are to:

• Reduce the accident rate on the road, which is currently at twice the national average;
• Improve the substandard horizontal and vertical alignments; and
• Improve the unreliable journey times that currently exist due to the regular platooning of vehicles behind slow moving vehicles.

Figures 0.1 and 0.2 below show the traffic volumes 'before' and 'after' scheme opening.
Figure 0.1 (450KB PDF)
Figure 0.2 (270KB PDF)

This Traffic Impact Study (TIS) Report summarises the main traffic effects of this scheme which were as follows:

• Daily traffic flows on the new improved section rose from around 22,400 vehicles per day (vpd), before opening, to 25,700 vpd after opening. An increase of 3,300 vpd, indicating a number of vehicles being drawn in from other areas.
• There are Journey Time savings of up to seven minutes for movements along this new improved route. This represents a significant time saving over the 15km Journey Time route, representing an average speed increase of 42kph, from 55kph to 97kph. Therefore the improvements have been successful in decreasing Journey Times along the route, and making the journey times more reliable.
• There is also an increase in traffic on some of the minor roads either side of the new improved section, reflecting new junction arrangements to access the improved route.

A11 roudham heath - attleborough improvements Introduction

A11 Roudham Heath - Attleborough Improvements

1. Introduction

1.1   This report outlines the results of traffic surveys carried out to monitor the effects of the A11 Roudham Heath to Attleborough Improvement scheme. The A11 forms part of the core National Route, linking London, Cambridge and the northern part of East Anglia. The Roudham Heath to Attleborough Improvement Scheme is one of three schemes on the A11 south of Norwich. There is also to be a bypass of Attleborough and an improvement scheme between Fiveways and Thetford. The three schemes are illustrated in Figure 1.1. below. The Roudham Heath to Attleborough Improvement Scheme, which is 9.9km (6.2 miles) in length, bridges the missing link of dual carriageway between Roudham Heath and Attleborough. The improvements included within the scheme are illustrated in Figure 1.2. overleaf.

1.2   The new carriageway of the A11 between Roudham Heath and Attleborough was officially opened on the 19th March 2003. 'Before' and 'After' traffic data for the area around the scheme was collected immediately prior to and after the opening date in order to prepare a Traffic Impact Study (TIS) on the effects of the scheme opening. In addition, Highways Agency count sites have been used to evaluate the effects of the A11 Roudham Heath to Attleborough Improvements on strategic routeing patterns in the local and wider area.

1.3   Section 2 of this report discusses the data collected as part of the TIS study. Sections 3 and 4 summarise the main results and conclusions, respectively.
Figure 1.1 (91KB PDF)
Figure 1.2 (80KB PDF)

A11 roudham heath - attleborough improvements Data collected

A11 Roudham Heath - Attleborough Improvements

2. Data Collected

2.1   This Traffic Impact Study (TIS) for the A11 Roudham Heath - Attleborough Improvement Scheme included the following surveys.

'Before Surveys'

• 6 Highways Agency permanent Automatic Traffic Count sites (ATC), located on the A11;
• 8 Norfolk County Council sites;
• Journey Time Survey (JTS) undertaken on 30 May 2001, before the improvement scheme.

'After Surveys'

• The 'After' surveys mirror the 'Before' surveys, with an up-to-date Journey Time Survey undertaken on 29th April 2003.

2.2   The details of the 'Before' and 'After' surveys are described below.

AUTOMATIC TRAFFIC COUNTS (ATC)

2.3   The 'Before' study comprised surveys at fourteen Automatic Traffic Count (ATC) sites; the locations of which are described below. There were five HA Count Sites on the A11, and one on the A47, and two County sites on the A140, at the following locations:

• A11- Elveden;
• A11 - South of Thetford;
• A11 - South of the scheme at Roudham;
• A11 - Hargham, South of Attleborough, on the new improved section;
• A11 - North of Wymondham;
• A47 - North Tuddenham;
• A140 - North of Long Stratton (near B1135);
• A140 - South of Long Stratton.

A further six county sites were used on the surrounding minor roads. They were at the following locations:

• Harling Road;
• Northend Lane;
• Two at Heath Road;
• Hargham Road;
• London Road.

2.4   For the 'After' study, the ATC sites used for the 'Before' counts were repeated in order for changes in traffic flows to be identified.

JOURNEY TIME SURVEYS

2.5   'Before' surveys were undertaken on Wednesday 30th May 2001 and the 'After' surveys on Thursday 29th May 2003.

2.6   Journey Time (JT) surveys were undertaken on the A11, as identified in Figure 2.1 below. The survey runs started from the end of the dual carriageway at Roudham Heath and finished at the start of dual carriageway north of Attleborough. The surveys were undertaken over the morning (0800 - 0900 hours) and evening (1700 - 1800 hours) peak periods, as well as an inter-peak period (1000 - 1500 hours).

Figure 2.1 (1260KB PDF)

Figure 2.1 - Journey Time Route along the A11

A11 roudham heath - attleborough improvements Summary of results

A11 Roudham Heath - Attleborough Improvements

3. Summary of Results

AUTOMATIC TRAFFIC COUNTS (ATC)

3.1   Figure 3.1 and 3.2 below summarise the 'Before' and 'After' ATC data using five day average two-way flows. A summary results table is included in Annex A of this report.

Figure 3.1 (268KB PDF)

3.2   Following scheme opening on 19th March 2003 it is evident that there is a noticeable increase in the volume of traffic travelling along the A11. Around 25,700 vehicles per day (vpd), on average, used the new improved section, which represents an increase of 3,300 vpd prior to the scheme opening.

3.3   On the A11, north of Wymondham, traffic volumes have changed by less than 1,000 vpd, increasing from 36,100 vpd to 37,000 vpd. South of Thetford on the A11 traffic volumes also increased by around 1,000 vpd, increasing from 27,900 vpd to 29,100 vpd. Thus it is only the central improved section that has seen a noticeable increase.

3.4   Traffic on the A47 at North Tuddenham between East Dereham and Norwich is largely unchanged following the introduction of this scheme, and traffic volumes have stayed around 22,300 vpd.

3.5   Also traffic volumes on the A140 south of Norwich are also largely unchanged, showing traffic volumes of 15,000 vpd south of Long Stratton and 21,000 vpd north of Long Stratton.

Figure 3.2 (260KB PDF)

3.5.1   From examination of the count data on the side roads accessing the A11, (Figure 3.2), traffic volumes on the B1111, Harling Road, has increased from 2930 to 3160 vehicles per hour, indicating an increase of over 7%.

3.6   Four of the six side road count sites show an increase in traffic volumes and the two northern side roads show a traffic volume decrease of around 100 trips.

MONTHLY AND DAILY TRAFFIC VARIATION

3.5   Figure 3.3 shows the monthly traffic volume variation trend in traffic across the year 2002 on the A11 at Roudham Heath, just south of the new scheme.

3.9   The highest and lowest average traffic flows are 17,800 in December and 24,500 in August, a difference of 37%, clearly indicating seasonal differences on the A11.

3.10   Due to Sunday markets and occasional touring car events at Snetterton we have looked at the daily variation in traffic volumes in that area. We have data from a site on the A11 at Hargham, in June 2003.

3.11   The daily variation shows that there is a peak on Friday, but most significantly, Sundays have the second highest traffic volume, indicating that Snetterton market attracts a lot of traffic in this area at the weekend. Below is an hourly profile of traffic in this area on Sunday.

3.12   There are two noticeable peaks in traffic volumes, one between 11am and noon, and the other between 5pm and 6pm, possibly indicating the times when market visitors arrive and depart.

JOURNEY TIME ROUTES

3.13   In order to look at changes in Journey Times, data collected in May 2001, as part of the ‘Before’ surveys, have been compared to data collected in April 2003, post opening. A summary of the Journey Times and Journey Speeds is shown in Table 3.1 and 3.2 respectively.

Table 3.1 – Comparative "Before" & "After" Journey Time Surveys

Direction	Period	Average Time (Before)	Average Time (After)	Time Saved After Improvements
Northbound	AM	16:14	09:38	06:36
	INTER	12:27	09:21	03:06
	PM	16:34	09:26	07:08
Southbound	AM	14:53	09:55	04:58
	INTER	11:52	09:46	02:06
	PM	16:07	09:59	06:08

3.13.1   Table 3.1 shows that Journey Times have been reduced significantly between Roudham Heath and Attleborough, particularly in the peak hours, where journey time savings of around 6 - 7 mins are being observed.

Table 3.2 – Comparative "Before" & "After" Journey Time Surveys

Direction	Period	Average Speed (Before)	Average Speed (After)	Increase In Speed
Northbound	AM	56	95	39
	INTER	74	98	24
	PM	55	97	42
Southbound	AM	62	92	30
	INTER	77	94	17
	PM	57	92	35

3.14   Table 3.2 shows that the average speeds along the improved A11 have increased quite substantially. Traffic speeds have increased from 55 - 75 kph before widening to around 95kph after opening. Table 3.2 also shows the consistent journey speeds across all periods of the day compared to the variable journey speeds shown before widening, where inter peak speeds are 75kph and peak speeds 55kph. Clearly, therefore, journey times and speeds are more reliable after widening of the A11.

A11 roudham heath - attleborough improvements Conclusions

A11 Roudham Heath - Attleborough Improvements

4. Conclusions

4.1   The traffic volumes on the A11 south of Norwich seem to have increased after the opening of the A11 Roudham Heath - Attleborough improvement. South and north of the improved section, the increase is shown to be around 1,000vpd, but on the improved section itself, the increase is shown to be over 3,000vpd.

4.2   There is no corresponding decrease on alternative routes such as the A140 or A47, suggesting either:

• New trips have been generated by the improvement; and / or
• Local redistribution of side road traffic around the improved section has increased traffic volumes on certain sections.

4.3   The results of the side road count data suggest that there is an increase of side road traffic onto the A11 at the southern end and a reduction at the northern end which does suggest that local traffic is accessing the A11 further south in order to travel north to Norwich as opposed to using the B113 or B1108 into Norwich as used previously.

4.4   The monthly variation of traffic volumes shows that there is a large seasonal change, with August traffic volumes being 37% higher than in the winter months. Traffic volumes are highest on a Friday/Sunday and the impact of Snetterton Sunday market shows high traffic volumes at Hargham on a Sunday morning as traffic accesses and leaves the market.

4.5   The traffic data collected as part of this Traffic Impact study demonstrates that the new A11 Roudham Heath to Attleborough Improvements scheme has been very successful in reducing journey times, and improving journey time reliability on the route.

4.6   Journey times over the section improve by up to seven minutes and speeds increase from 55kph to 95kph, with 95kph being shown for all time periods of the day after opening.

4.7   The One Year 'After' Count for this scheme's Post Opening Project Evaluation will be undertaken in March / April 2004.

A11 roudham heath - attleborough improvements Annex A

A11 Roudham Heath - Attleborough Improvements

Annex A

Journey Time Results Summary Table

		Before		After
Direction	Period	Av. Time (MM:SS)	Av. Speed (KPH)	Av. Time (MM:SS)	Av. Speed (KPH)	Time Saving (MM:SS)	Av. Speed Difference (KPH)
NORTHBOUND	AM	16:14	56	09:38	95	06:36	39
	INTER	12:27	74	09:21	98	03:06	24
	PM	16:34	55	09:26	97	07:08	42
SOUTHBOUND	AM	14:53	62	09:55	92	04:58	30
	INTER	11:52	77	09:46	94	02:06	17
	PM	16:07	57	09:59	92	06:08	35

Results Summary Table - Traffic Counts

Site No.	Description	Data Source	5-Day Average Two Way Traffic Flow (AWT)		5-Day	7-Day Average Two Way Traffic Flow (ADT)		7-day
			Before Opening (Mar 2003)	After Opening (Mar 2003)	% increase between 'Before' & 'After'	Before Opening (Mar 2003)	After Opening (Mar 2003)	% increase between 'Before' & 'After'
9903/4	A11 Elveden	HA	22200	23200	4.5	21100	22200	5.2
9503/4	A11 Thetford Bypass	HA	27900	29100	4.3	25900	27500	6.2
9505/6	A11 Roudham Heath	HA	22100	23600	6.8	21200	23100	9
9501/2	A11 Hargham (New Improved Section)	HA	22400	25700	14.7	21200	24700	16.5
9509/10	A11 Wymondham	HA	36100	37000	2.5	33700	34600	2.7
9535/6	A47 North Tuddenham	HA	22300	22300	0	20700	20700	0.0
	A140 (North of) Long Stratton	county	20600	21000	1.9	19500	20200	3.6
	A140 (South of) Long Stratton	county	15200	15100	-0.7	14400	14500	0.7
			Before Opening (Feb 2003)*	After Opening (Mar 2003)	% increase between 'Before' & 'After'	Before Opening (Feb 2003)	After Opening (May 2003)	% increase between 'Before' & 'After'
1	Harling Road, Roudham	county	2930	3160	7.8	2690	3030	12.6
2	Northend Lane, Snetterton	county	480	680	41.7	420	610	45.2
3	Heath Road, Snetterton	county	2150	2300	7	1920	2270	18.2
4	Hargham Road, Quidenham	county	1700	1590	-6.5	1480	1310	-11.5
5	London Road, Attleborough	county	4350	4280	-1.6	3970	4120	3.8
6	Heath Road, Snetterton	county	1340	1540	14.9	1320	1570	18.9

* Feb 2003 county count site results have been factored by 1.0997 to represent May 2003 traffic levels. This is to reflect any seasonal variation between Feb and May.