One Year After Study: A6 Clapham Bypass

One Year After Study: 

A6 Clapham Bypass 

March 2005

SFM/PIES 2000 COMMISSION 

ONE YEAR AFTER STUDY - A6 

Clapham Bypass 

JOB NUMBER: 4416516\600 

DOCUMENT REF: A6 Clapham Bypass 1 Yr 

FINAL.doc 

01 Draft Report SG JM PR PR Nov 2004 

02 Incorporate HA and BCC 

comments and Executive 

Summary 

SG PW PR PR Mar 2005 

Originated Checked Reviewed Authorised Date 

Revision 

Purpose 

Description


ONE YEAR AFTER STUDY - A6 Clapham Bypass 

Contents 

Section 

Executive Summary 

Page 

iii 

1. Introduction 1-1 

2. Data Collection and Evaluation 2-1 

Data Collection 2-1 

‘Before’ Surveys 2-1 

‘After’ Surveys 2-1 

Summary of Results 2-4 

Journey Times 2-6 

Journey Speeds 2-7 

Vehicle Classification 2-8 

3. POPE Methodology 3-1 

Introduction 3-1 

Vehicle Hour Benefits 3-1 

Changes in Journey Time 3-2 

Changes In Accident Benefits 3-4 

Summary of POPE Methodology 3-5 

4. Economic Benefits of the Two Schemes 4-1 


COBA Re-evaluation 4-1 

Re-Evaluation of Scheme Costs 4-3 

5. Evaluation Summary Table 5-1 


Appraisal Summary Tables (AST) 5-1 

Outturn Effects 5-4 

6. Summary of Conclusions 6-1 

List of Tables 

Table 2.1 - Journey Times along the A6 between Bedford and Milton Ernest 2-7 

POPE _ A6 Clapham OYA _ final 

i



Table 2.2 - Journey Times along the A6 between Bedford and Milton Ernest 2-8 

Table 2.3 – Proportion of Traffic by Vehicle Type Using the Old A6 2-8 

Table 3.1 - Comparison of forecast and actual vehicle hours for Clapham along the bypass 

and bypassed links. 3-3 

Table 3.2 – Journey Time Benefits 3-3 

Table 3.3 - Comparison of POPE Outurn and Predicted Journey Time Benefits 3-3 

Table 3.4 – Comparison of actual and predicted number of accidents at Clapham along the 

bypass and bypassed links 3-4 

Table 3.5 – Accident Benefits 3-4 

Table 3.6 – Comparison of POPE Outturn and Predicted Accident Benefits 3-5 

Table 4.1 – Comparison of OPR AST and Revised COBA analysis 4-2 

Table 4.2 – Conversion of POPE Methodology Benefits for OPR AST Comparison 4-3 

Table 4.3 – Predicted and Outturn Scheme Costs 4-3 

Table 5.1 – AST for A6 Clapham Bypass 5-3 

Table 5.2 – Summary of Accidents on the A6 One Year Before 5-5 

Table 5.3 – Summary of Accidents on the old A6 and Bypass One Year After 5-5 

Table 5.4 – Accident Severity Splits Before And After 5-5 

Table 5.5 – EST for A6 Clapham Bypass 5-10 

List of Figures 

Figure 0.1 – Daily Traffic Flows ‘Before’ and ‘After’ Scheme Opening 

iii 

Figure 1.1 - A6 Clapham Bypass Wider Area Context 1-1 

Figure 1.2 – A6 Clapham bypass 1-2 

Figure 2.1 - Location of Traffic Count Sites 2-3 

Figure 2.2 - Journey Time Survey Routes 2-4 

Figure 2.3 - Traffic Volume Changes around Clapham 2-5 

Figure 5.1 – Accidents One Year Before the Opening of the A6 Clapham Bypass 5-7 

Figure 5.2 – Accidents One Year After the Opening of the A6 Clapham Bypass 5-8 


ii



Executive Summary 

The A6 Clapham Bypass officially opened on 12 th December 2002, as illustrated in Figure 

0.1 below. The scheme consists of a 5 km long new section of dual carriageway road, 

diverging from the current A6 on the northern outskirts of Bedford and rejoining the trunk 

road north of Clapham towards Milton Ernest. ‘Before’ and ‘After’ traffic data for the bypass 

was collected immediately prior to and one year after scheme opening. In addition, traffic 

data from surveys on County roads from Bedfordshire County Council and existing 

Highways Agency permanent count sites was obtained to evaluate the effects of the opening 

of the bypass on strategic traffic routing patterns in the area. 

Figure 0.1 – Daily Traffic Flows ‘Before’ and ‘After’ Scheme Opening 

The main effects of scheme opening are as follows: 


iii



 

Approximately 18,500 vehicles per day are using the A6 Clapham Bypass one 

year after opening. Traffic volumes in the south of Clapham on the old A6 

dropped from 23,000 to 8,500 vehicles per day (vpd) denoting a decrease of 

around 62% in traffic through Clapham. There has also been a reduction of 

vehicles on the old A6 north of Clapham at Oakley Hill, where there has been a 

decrease from 14,500 vehicles per day to 1,700 vehicles per day, a decrease of 

88%. This decrease reflects the fact that this section of road between Highfield 

Road and the northern tie-in of the scheme is now southbound only, i.e. there is 

no northbound access to the A6, north of Oakley Road. 

Therefore the scheme has been successful in significantly reducing traffic 

volumes on the A6 through Clapham. 

 

 

 

 

 

The scheme has also been successful in reducing journey times on the A6 in 

that journey time savings of between 2 to 3 minutes are shown for most 

movements that previously used the A6 through Clapham. 

In addition to the reduction in traffic along the old A6 the proportion of HGV’s 

through Clapham dropped from 8% to 2% after the bypass opened. 

There has also been re-routing of traffic on the local roads in the area, for 

example; 

Traffic volume reductions of nearly 600 vehicles per day were recorded on 

Highfield Road between Oakley and north of Clapham, as traffic volumes fell 

from 5,200 vehicles per day to 4,600 suggesting a switch of traffic from 

villages such as Felmersham and Radwell who used to access the A6 via 

Oakley Road / Highfield Road, but post opening of the new scheme, now 

access the A6 at Milton Ernest. 

There are observed traffic volume increases of over 1,100 vehicles per day on 

Oakley Road, west of the Bypass, increasing from 6,200 vehicles per day to 

7,300 vehicles per day as a result of scheme opening, however there has 

been a corresponding decrease of 500 vehicles per day on Church Road 

which is road to Bromham suggesting that local journeys from Oakley to 

Bedford have re-routed to access the southbound Clapham Bypass rather 

than Church Road to Bromham and the A428. 

East of the Bypass on Oakley Road, traffic volumes fell by 1,700 vehicles per 

day as a result of scheme opening. 

The initial analysis accident data collated for the opening year indicates that the 

A6 Clapham Bypass has led to a reduction in the number of accidents in the 

corridor, where up to 7 personal injury accidents have been saved in the first 

year after opening. 

Comparison of the forecast benefits in the Appraisal Summary Table at the 

Order Publication Report stage with the outturn benefits of the scheme show that 

the prediction of the relief of traffic in Clapham was robust and that the accident 

savings predicted were also robust. 


iv



1. Introduction 

Background 

1.1 The A6 Clapham Bypass officially opened on the 12 th December 2002. The scheme 

consists of a 5 km long new section of dual carriageway road, diverging from the 

current A6 on the northern western outskirts of Bedford and rejoining the trunk road 

north of Clapham south of Milton Ernest. The A6 Clapham Bypass has been named 

‘Paula Radcliffe Way’. 

1.2 The location of the improvements in the wider regional context is illustrated in Figure 

1.1. The scheme provides 2 interchanges from the bypass onto Oakley Road and 

Highfield Road. 

Figure 1.1 - A6 Clapham Bypass Wider Area Context 

1.3 Figure 1.2 shows the completed scheme in more detail. 


1-1



Figure 1.2 – A6 Clapham bypass 

1.4 In order to assess the immediate responses to the new scheme, ‘Before’ and ‘After’ 

traffic volume data on the A6 and other competing routes was collected immediately 

prior to and after opening in December 2002 to monitor the effects of the new 

scheme. 

1.5 In addition, traffic data from surveys on County roads from Bedfordshire County 

Council and existing Highways Agency permanent count sites was obtained to 

evaluate the effects of the opening of the A6 Clapham Bypass on strategic traffic 


1-2



routeing patterns in the area and the effects of this immediate response to the 

improvements was reported in the Traffic Impact Study Report. 

Scheme Objectives 

1.6 The A6 improvement is a scheme within the Highways Agency’s Road Programme 

called the Targeted Programme of Improvements (TPI). The scheme was 

implemented to address the following problems, which are listed within the scheme 

Appraisal Summary Tables (AST). These problems were: 

 

 

 

Noise and air quality problems in Clapham. 

Accidents due to pedestrian and vehicle conflict plus a poor standard single 

carriageway. 

Increased journey times due to having to travel through a built up area. 

Purpose of the Report 

1.7 This report represents the ‘One-Year After’ report for the A6 Clapham Bypass 

improvement scheme. This report has been prepared as part of the Post Opening 

Project Evaluation (POPE) Commission and builds on the Traffic Impact Study (TIS) 

report prepared for the Highways Agency in April 2003. 

1.8 This report will set out a number of assessments, namely: 

A comparison of the ‘Before’ and ‘After’ traffic volumes on the A6 and other 

roads in the corridor and illustrate how traffic volumes have changed since the 

opening of the A6 Clapham Bypass; 

A comparison of ‘Before’ and ‘After’ journey times on the A6; 

 

 

It will also present an evaluation of predicted and outturn economic forecasts 

based on changes in journey times as well as other outturn effects in the form of 

an Evaluation Summary Table (EST); and 

The report will also outline the changes in accidents on the route and whether 

they have changed since the opening of the A6 Clapham Bypass. 

1.9 This report specifically considers the re-evaluation of the predicted benefits for the A6 

Clapham Bypass. The three main elements involved are: 

 

 

 

To identify the costs and benefits originally forecast for the scheme at Order 

Publication Report (OPR) stage; 

To quantify the outturn (actual) costs and the outturn level of benefits actually 

accruing, based on outturn traffic volume and journey time data for the scheme; 

and 

To compare the results and quantify the difference in the Present Value of 

Benefits (PVB). 

1.10 Following this introduction the report has been divided into five further sections as 

follows: 

 

Section 2 outlines existing data collation and new data collection and reports on 

traffic volume and journey time changes attributable to the A6 Clapham Bypass; 


1-3



 

 

 

 

Section 3 presents an assessment of predicted and outturn economic benefits 

using the POPE journey time and accident reduction methodology; 

Section 4 presents the original economic results, calculated by the Department 

for Transport’s program COBA for these schemes and the level of benefits that 

would have been forecast if outturn traffic volumes and journey times were 

known at the time. The section also compares the COBA and POPE 

methodology; 

Section 5 presents the original Appraisal Summary Tables (AST) for the A6 

Clapham Bypass and then re-evaluates these predictions within an Evaluation 

Summary Table (EST). The section also gives an early indication of changes in 

the number of accidents in the corridor; 

Section 6 summarises the main conclusions from the evaluations and the 

limitations to use. 

1.11 It should be noted, that the ‘One-Year After’ report is primarily focused on the 

evaluation of Economy and Safety sub-objectives of the GOMMMS Appraisal. 

Environmental evaluation has not been carried out at this stage, but will form part of 

the ‘5-Year After’ evaluation. 


1-4



2. Data Collection and Evaluation 

DATA COLLECTION 

2.1 This One Year ‘After’ Report for the A6 Clapham Bypass includes the following 

surveys: 

‘BEFORE’ SURVEYS 

3 Highways Agency Automatic Traffic Count (ATC) surveys on the A6; 

 

 

 

4 ATC surveys by Bedfordshire County Council; 

Journey time surveys undertaken in April 2002 on the existing A6 route and 

adjoining roads. Journey time surveys were undertaken at this time to ensure 

normal operating conditions. 

Turning count data for the A6 at the junctions for Oakley Road and Highfield 

Road. 

‘AFTER’ SURVEYS 

2.2 Due to the de-trunking of the A6 in the period between the Traffic Impact Study and 

the One Year After Report, the responsibilities for the count sites had altered and the 

Highways Agency ATC sites were no longer operational. In circumstances where 

data was no longer readily available from the sources used for the ‘Before’ or TIS 

surveys, alternative means were used to provide re-assessment at the same 

locations used for the ‘Before’ study and the TIS. The survey programme can be 

summarised as: 

 

 

 

 

 

2 former Highways Agency ATC sites on the A6 Clapham Bypass and A6 

Bedford Road, Knotting were re-fitted with counters by Northern Link Traffic Data 

Consultancy in June; 

2 temporary ATC count sites were placed on the old A6 between 10 th May and 

24 th May, one at a former HA permanent ATC site by Northern Link Traffic Data 

Consultancy ; 

3 Bedfordshire temporary ATC site locations around Oakley plus one permanent 

site on the A6 South of Milton Ernest which BCC monitors annually in Spring; 

Journey time surveys. Consistent with the additional journey time survey on the 

Bypass conducted for the TIS, this survey was reassessed for the One Year 

‘After’ Report; and 

12 hour turning count data for 6 junctions conducted by Count on Us on the 12 th 

May. 

2.3 The details of the ‘Before’ and ‘After’ surveys (with OSGR’s for site locations) are 

described below. 


2-1



Automatic Traffic Counts 

2.4 Atkins undertook automatic traffic count (ATC) surveys in May and June 2004 at the 

following sites (Counts are volumetric unless stated otherwise): 

 

 

 

 

A6 Clapham Bypass between Northbound Slip and Oakley Road Interchange; 

A6 Bedford Road, Knotting - Classified count, vehicles greater than 5.2metres; 

Old A6 Clapham, South of Green Lane on road sign; and 

Old A6 Clapham, North of Oakley Road on road sign. 

2.5 In order to ascertain the effects of the Bypass on the roads in the Oakley area, 

Bedfordshire County Council undertook counts at three ATC on the adjoining roads 

and provided data from counts between Milton Ernest and the bypass in May as part 

of their annual monitoring. The locations of these counts are listed below. 

Highfield Road on the West side of the bypass (501360,254075); 

Church Lane (500580,252800); 

Oakley Road on the West side of the bypass (502000,252925); and 

A6 between Milton Ernest and Bypass (501930,254810). 

2.6 Classified turning counts were also conducted at six junctions. Vehicles were divided 

into Cars, Light Vehicles, Heavy Goods Vehicles 1, Heavy Goods Vehicles 2 and 

Passenger Service Vehicles. The locations of the six sites are detailed below. 

 

 

 

 

 

 

Highfield Road/ Milton Road/ A6 South off-slip; 

Highfield Road/ A6 South on slip; 

Highfield Road/ A6 North on-off slip; 

Milton Road/Oakley Road; 

Oakley Road/ A6 South on-off slip; and 

Oakley Road/ A6 North on-off slip. 


2-2



Journey Time Surveys 

Figure 2.1 - Location of Traffic Count Sites 

2.7 Four journey time surveys were undertaken on four routes, identified as ‘blue’, ‘pink’, 

‘orange’ and ‘green’ routes, which are illustrated in Figure 2.2 with the respective 

timing points used for each route. The ‘blue’ route represented the old A6 between 

Milton Ernest and the A6 Clapham Road / Shakespeare Road roundabout south of 


2-3



Clapham, whereas the ‘green’ route was an ‘after’ survey only on the new bypass 

between the same two points. The ‘pink’ and ‘orange’ routes were used to derive 

estimates of journey time change form Oakley to the A6 on Highfield Road and 

Oakley Road respectively. 

2.8 ‘Before’ journey time surveys previously undertaken on Tuesday 24 th April 2002 were 

used for comparison with the One Year After surveys undertaken between Monday 

17 tth and Wednesday 19 th May 2004. Survey periods were the morning (07:30 – 

09:00) and evening (16:30 - 18:00) peaks, and an inter-peak period (10:00 -11:30). 

Figure 2.2 - Journey Time Survey Routes 

SUMMARY OF RESULTS 

Traffic Volume Changes 

2.9 Figure 2.3 below shows the changes in daily traffic volumes on the A6 and other 

roads in the area. The ‘Before’ and ‘TIS After’ counts have been adjusted up to 

reflect May 2004 traffic levels to ensure the conclusions drawn take into account 

seasonality and normal traffic growth. This has been done by using the seasonally 

adjusted traffic growth index 1 to determine normal background growth between the 

1 Department for Transport (2004) ‘Traffic in Great Britain, Q2 2004’ 


2-4



count data and an index to adjust the average daily traffic flow based upon monthly 

seasonal variations in traffic flow. 2 

Figure 2.3 - Traffic Volume Changes around Clapham 

2.10 The main points to note for traffic volume changes on the A6 around Clapham are: 

2 Department for Transport (2004) ‘Road Traffic Statistics : 2003’ 


2-5



 

 

The traffic volume data collected as part of this study demonstrates that the A6 

through Clapham carried approximately 15,000 to 23,000 vehicles per day (vpd) 

before the opening of the bypass. One year after opening, this has dropped to 

approximately between 2,000 to 8,500 vehicles per day clearly indicating that 

the scheme has been successful in routeing vehicles away from the 

village; 

A year after opening the traffic on the bypass has risen to around 18,500 vpd 

from about 17,000 vpd, an increase of around 9%. 

This level of growth is above the normal increase in traffic flow, and thus it 

seems likely that the A6 scheme has drawn some additional traffic into the 

corridor in the form of new trips and re-assigned traffic. 

At the time of Traffic Impact Study local traffic had been reduced by 1,500 

vehicles per day on Highfield Road which was likely to be due to re-routing of 

trips from wider areas in the Northwest such as Odell and Felmersham joining 

the A6 Bypass at Milton Ernest where previously they would have joined the A6 

at Clapham. Although traffic flows along Highfield Road have increased slightly 

the since the TIS, flows on this road are still 11% lower than before the bypass 

opened. 

 

There is no evidence of the bypass resulting in a diversion of traffic from the 

Bromham area through Oakley to join the Bypass with traffic levels through 

Church Lane, which is the corridor linking Bromham and Oakley experiencing a 

slight decrease from 7,900 vpd before opening to 7,400 one year after. 

JOURNEY TIMES 

2.11 Journey time surveys were undertaken on the key corridors between Bedford and 

Milton Ernest and between Oakley and Clapham which would benefit from the 

Bypass. 

2.12 The surveys covered the full A6 Bypass from the Bedford Roundabout up to Milton 

Ernest and the same start and finish points but using the old A6 instead. Journey 

times were also surveyed from the old A6 to Oakley via Highfield Road and Oakley 

Road respectively. 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). 

2.13 The ‘before’ and ‘after’ survey periods were December 2002 and May 2004 

respectively, and thus the time savings shown reflect the completion of the A6 

Clapham Bypass. 

2.14 The journey time survey results are shown in Table 2.1 below. For the One Year 

After Study, a further analysis of the before data indicated some delay impacts 

attributable to the bypass construction affecting the before data used in the TIS and 

these delays have been removed from the journey times. Therefore the ‘Before’ 

figures used in the One Year After Study do not reflect what was used in the TIS. 


2-6



Journey Time (Minutes) 

Direction Period Before 

(April 02) 

After 

(December 

02) 

1 Year After 

(May/June 

04) 

Saving 

(Before and 

1 Year 

After) 

Northbound 

AM Peak 07:24 05:22 04:30 02:54 

Inter Peak 07:12 05:13 04:35 02:37 

PM Peak 07:16 05:14 04:46 02:30 

Southbound 

AM Peak 07:10 04:59 07:47 -00:37 

Inter Peak 07:51 05:01 04:28 03:23 

PM Peak 06:59 04:55 04:54 02:05 

Table 2.1 - Journey Times along the A6 between Bedford and Milton Ernest 

2.15 From the Journey Time data it suggests that vehicles travelling Northbound are 

saving approximately two and a half minutes per journey all day which is an increase 

on the TIS saving of about 30 seconds to a minute. This saving is also evident 

southbound with the exception of in the AM peak where there is indication of an 

increase in journey time. 

2.16 Further examination of this increased journey time southbound in the AM Peak 

indicates that heavy congestion is occurring in the area by the new roundabout at the 

southern end of the bypass at about 8:30 which is increasing journey times 

significantly and increasing the average AM peak journey time which is generally 

between 4 and 5 minutes before 8:30. This congestion is also evident on the old A6 

journey time surveys around the same time period and the congestion was 

experienced on two different days indicating that the congestion is likely to be due to 

the traffic volumes approaching Bedford at that time as opposed to any unusual 

occurrences affecting the surveys. 

2.17 It should also be noted that in conjunction with the bypass a new 50 mph zone 

complete with safety cameras operated by Bedfordshire and Luton Safety Camera 

Partnership was established on the A6 between Milton Ernest and the northern end 

of the bypass. This will impact the journey time surveys on the timing points on this 

section for the One Year After Surveys. 

JOURNEY SPEEDS 

2.18 Based upon the information compiled for the journey time surveys, Table 2.2 

compares the Journey Speeds ‘Before’, ‘After’ and ‘One Year After’ scheme opening. 

Average speeds on the new A6 bypass are between 11kph and 26kph faster 

depending on direction of travel and time of day. 


2-7



Journey Speed (Minutes) 

Direction Period Before 

(April 02) 

After 

(December 

02) 

1 Year After 

(May/June 

04) 

Saving 

(Before and 


After) 

Northbound 

AM Peak 62 69 82 20 

Inter Peak 63 71 81 18 

PM Peak 63 71 78 15 

Southbound 

AM Peak 64 75 64 0 

Inter Peak 58 74 84 26 

PM Peak 65 76 76 11 

Table 2.2 - Journey Speeds along the A6 between Bedford and Milton Ernest 

VEHICLE CLASSIFICATION 

2.19 The manual turning counts provided classified data in addition to volumetric counts. 

Turning counts were conducted for the ‘Before’ Study at the junction between the A6 

and Oakley Road, and the roundabout between the A6 and Highfield Road. These 

counts were repeated for the One Year ‘After’ Study in addition to turning counts at 

the slip roads on the Bypass. 

2.20 Classification of vehicles was Cars, Light Goods Vehicles (LGV’s), Heavy Goods 

Vehicles (HGV’s) and Public Service Vehicles (PSV’s). In addition to determining the 

actual changes in traffic flows through the village, the classified counts provide 

information about the effect the bypass has had on individual vehicle types. 

2.21 In addition to the reduction in traffic along the old A6, Table 2.3 shows that between 

the hours of 7:00 to 19:00, the proportion of HGV’s as total traffic through Clapham 

dropped from 8% to 2% after the bypass opened. The Manual Classified Count 

conducted at Milton Ernest indicates that HGV’s still comprises of approximately 7% 

of traffic along the corridor and that the bypass has clearly been successful in rerouting 

HGV’s out of Clapham, and onto the bypass. 

Car 

LGV 

HGV 

OGV 

Vehicle Type Before Study After Study Change 

80% 86% 6% 

11% 10% -1% 

8% 2% -6% 

1% 2% 1% 

Table 2.3 – Proportion of Traffic by Vehicle Type Using the Old A6 


2-8



3. POPE Methodology 

INTRODUCTION 

3.1 As part of this One-Year After Study, the Report is also assessing the predicted level 

of economic benefits. This section assesses the level of economic benefits predicted 

for the A6 Clapham bypass and compares these predictions with actual benefits 

accrued when considering actual traffic volume changes and actual journey time 

benefits. 

3.2 The approach that we have taken is termed the Post Opening Project Evaluation 

(POPE) methodology. The basis of the POPE methodology is that through previous 

COBA evaluations undertaken it has been identified that the majority of benefits are 

derived primarily from two areas: 

 

 

Link Transit time (vehicle hours) benefits; and 

Accident Benefits. 

3.3 As such, link transit time, (which is represented by traffic volumes multiplied by 

journey times) and the number of accidents can be collected before and after 

scheme opening and the difference between these observed values can be 

compared to the difference shown in time and accidents for the same links shown in 

the OPR COBA’s. The premise of the POPE methodology is that the change in the 

observed flows, times and accidents can be directly associated to the economic 

benefits predicted for this scheme. 

3.4 The following section outlines this approach in more detail. 

VEHICLE HOUR BENEFITS 

3.5 To calculate link transit time or vehicle hour benefits, the COBA deck from OPR must 

be available, and the following changes implemented so that sensible and like-for-like 

comparisons can be made: 

 

 

 

 

OPR - Do Minimum: Although flow and delay data was probably collected prior 

to scheme implementation at the OPR stage, journey time and delay information 

must be determined by re-running the COBA deck with a journey time year set to 

the same as that when the Post Opening surveys were undertaken; 

OPR - Do Something: As with the OPR Do Minimum this data will need to be 

determined from re-running the COBA deck for the survey year after opening; 

Actual - Do Minimum: Pre opening count and journey time data is collected for 

each new scheme route before opening. This information is obtained for the AM, 

IP and PM time periods; and 

Actual - Do Something: Traffic volumes and journey times from surveys after 

the opening of the schemes are directly applicable to this scenario. 

3.6 The original Appraisal Summary Table published was in July 1998 and subsequently 

a revised COBA was produced in 2001. The benefits of the revised version differ 

from what was originally published in the AST and it is the revised COBA that has 


3-1



been used in the POPE analysis for this scheme which has been adapted to enable 

comparison between the original OPR AST and the POPE methodology. Both the 

differences between the benefits and the methodology used for the revised COBA 

benefits will be explained in detail in Chapter 5. All monetary benefits are in 1998 

resource prices discounted to 1998. 

3.7 In considering the changes between the COBA forecast benefits and the observed 

vehicle hour benefits, there are limitations bought about by the availability of data. 

Only peak hour and off peak hour journey times are available for the key links before 

and after opening, even though count data has been collated for the whole 24 hour 

period. 

3.8 This means that only the bypass and bypassed links (where data is available) are 

considered in the POPE assessment, and thus the change in vehicle hours can be 

compared with the change in link transit time for the same links in the OPR COBA. 

3.9 This test assumes that flow data, on key links, is available by hour for a 24 hour 

period and journey time data is only available for the peak and off peaks. This 

enables the proportion of total traffic travelling in the AM peak, PM peak and Off 

Peak and the application of the peak and off peak journey time to these proportions. 

3.10 For the COBA OPR expansion factors from peak hour to peak period and off peak 

period to all other hours have been calculated from the Do Minimum observed flow 

data. This has then been used to factor up the outturn data to a total average day. 

CHANGES IN JOURNEY TIME 

3.11 In conducting the analysis of link transit time the one year after traffic flows have 

been adjusted to remove any traffic growth due to induced traffic as a result of 

opening of the bypass because the flows indicate that there has been additional 

traffic growth on this corridor above the level of national growth. This suggests that 

the additional flows may have come from people who previously did not use the A6 

using the new bypass as it will reduce their overall journey time. As it is not possible 

to determine the journey time saving of these newly generated trips along the bypass 

the analysis focuses primarily on the savings related to flows removed from the old 

A6 onto the bypass. The assumption used do this was that all induced traffic along 

this corridor would be on the bypass and therefore in the after scenario, the flows on 

the bypass could be split into trips transferred from the old A6 and new trips along 

the corridor. 

3.12 The journey time data also enabled the additional savings of bypass users originating 

along Highfield Road and Oakley Road to be estimated as the bypass is located 

nearer to Oakley than the old A6 and therefore they will experience subsequent 

decreases in journey time equal to the journey time between the bypass slip road 

and the two roads respective junctions with the old A6. 

3.13 Table 3.1 shows the differences between the vehicle hours before and after opening 

of the bypasses (observed traffic volumes multiplied by journey times) and the 

differences between flow multiplied by the forecast journey times for the same links in 

the COBA OPR. 


3-2



Low Growth 

High Growth 

OPR COBA 

Do Minimum 466,027 562,214 

Do Something 317,868 354,408 

Difference 148,159 207,806 

Observed 

‘Before’ 622,423 622,423 

‘After’ 440,409 440,409 

Difference 182,013 182,013 

Table 3.1 - Comparison of forecast and actual vehicle hours for Clapham along the 

bypass and bypassed links. 

3.14 Table 3.1 shows that the saving in observed vehicle hours for the Clapham bypass is 

182,000 hours over the year. For the same links and scheme year, the Low Growth 

prediction was 148,000 and the High Growth prediction was 208,000. The COBA 

assessment showed that the Link Transit Time benefits for this scheme was £27.85m 

for the Low Growth Scenario and £40.92m for the High Growth Scenario. 

3.15 It was normal at the time of the OPR assessment for Low and High Growth to be 

weighted to create an average cost, by utilising 60% of the Low Growth result, and 

40% of the High Growth Result. We have retained this assumption when considering 

weighted growth in this report. Using the relationship between vehicle hours saved 

and economic benefit from the COBA analysis, the observed 182,000 hours saved 

correlates to £35.0m benefits. Table 3.2 compares the forecast and actual journey 

time benefits for the scheme. 

COBA Forecasts 

Actual 

Difference in 

Annual Vehicle 

Hours in 2003 


Journey Time 

Benefits 

Difference in 

Annual Vehicle 

Hours in 2003 


Journey Time 

Benefits 

Low Growth 148,159 £27.85m 182,013 £35.00m 

High Growth 207,806 £40.92m 182,013 £35.00m 

Table 3.2 – Journey Time Benefits 

3.16 The POPE comparison suggests that the forecast journey time benefits for the 

scheme is £33.1m compared with actual outturn benefits of £35.0m as shown in 

Table 3.3 -. The outturn journey time benefits are estimated to be approximately 6% 

higher than predicted. 

Predicted Benefits POPE Outturn Benefits Percentage difference 

£33.08m £35.00m 5.8% 

Table 3.3 - Comparison of POPE Outurn and Predicted Journey Time Benefits 


3-3



3.17 Two potential caveats exist with the journey time saving analysis using the POPE 

methodology and should be considered when interpreting these results. 

 

 

The POPE analysis does not consider any journey time savings for the new trips 

or reassigned trips which are drawn into the corridor. 

The impacts of the bypass on the section between the newly constructed south 

roundabout and the Manton Lane roundabout section have not been evaluated 

as no counts were made on this section. The indication from the One Year After 

Study is that congestion is occurring on this stretch of road which is the key route 

into Bedford from the A6 and also has the entrance to Sainsburys supermarket. 

Some of this congestion is likely to be due to the induced traffic generated by the 

bypass which has subsequently has caused negative journey time impacts on 

flows on this section and these increased journey times have not been included 

in the POPE analysis. 

CHANGES IN ACCIDENT BENEFITS 

3.18 Table 3.4 below shows the difference between the actual number of accidents before 

and after opening of the bypass and the difference between the numbers of 

accidents predicted by COBA. The observed ‘Before’ accidents are based on 

average annual accident rates for the 3 years before the scheme opening. 

OPR COBA 

Observed 

Low Growth High Growth 

Do Minimum 9.3 11.3 

Do Something 3.4 4.2 

Difference 5.8 7.1 

‘Before’ 13.0 13.0 

‘After’ 6.0 6.0 

Difference 7.0 7.0 

Table 3.4 – Comparison of actual and predicted number of accidents at Clapham 

along the bypass and bypassed links 

3.19 The COBA assessment showed that accident benefits were £9.54m for the 30 Year 

Appraisal period. This means that 7 accidents saved in 2003 correlates to £9.54m of 

accident benefits over the 30 year appraisal period. Table 3.5 shows the POPE 

estimates of accident benefits for High and Low growth. 

COBA Forecasts 

Actual 

Difference in 

number of 

accidents in 

2003 


Journey Time 

Benefits 

Difference in 

number of 

accidents in 

2003 


Journey Time 

Benefits 

Low Growth 5.8 £9.29m 7.0 £11.09m 

High Growth 7.1 £11.14m 7.0 £11.09m 

Table 3.5 – Accident Benefits 


3-4



3.20 Table 3.6 summarises the comparison of outturn and predicted accident benefits for 

the weighted growth. This shows that outturn accident benefits on the bypass and 

bypassed links were about 11% higher than forecast. 

Predicted Benefits POPE Outturn Benefits Percentage difference 

£10.03m £11.09m 10.6% 

Table 3.6 – Comparison of POPE Outturn and Predicted Accident Benefits 

SUMMARY OF POPE METHODOLOGY 

3.21 These results suggest that the POPE methodology may be a robust way of 

evaluating link transit time benefits, particularly when most of the key links have all 

been counted and journey times have been undertaken. 

3.22 The POPE methodology for accidents should be treated with caution, as it is normal 

for changes in accidents to be assessed over 3-5 years. Therefore, conclusions can 

only be considered as indicative when they are derived from only one year’s data. 

3.23 Thus, the POPE methodology will continue to be used on other schemes in order to 

provide a larger sample to verify POPE as an evaluation tool. 


3-5



4. Economic Benefits of the Two Schemes 

INTRODUCTION 

4.1 Economic benefits of a scheme have been traditionally assessed using the 

Government’s COBA (Cost Benefit Analysis) program, which considers changes in: 

 

 

 

Link transit time, which is the time on each affected link both before and after 

opening weighted by vehicle flows; 

Vehicle operating costs (VOC), reflecting fuel and other operating costs 

calculated by a change in total distance travelled on the affected links, but also 

considering vehicle speeds; and 

Accident rates and costs, which change after infrastructure improvements are 

made as accidents are normally less frequent on new roads. 

4.2 This section presents a comparison of predicted benefits as calculated by COBA and 

an assessment of what those benefits would be if the outturn traffic volumes and 

journey time savings were known at the time. 

COBA RE-EVALUATION 

4.3 The original Order under the Highways Act 1980 for the A6 Clapham bypass was 

made in 1992. The Appraisal Summary Table published for this scheme was for a 

1996 scheme (Version of 22 July 1998) and reflects the benefits put forward for 

public inquiry and the OPR. 

4.4 The relevant COBA data for the scheme published in the AST was unavailable but a 

revised COBA was produced by the DETR in November 2001. Although these were 

not the exact figures which the OPR would have been based, due to the time elapsed 

between the OPR and the construction of the bypass this revised COBA will be 

based on more accurate scheme specification and more recent economic and traffic 

growth forecasts over the 30 year appraisal period of the project. Therefore the 

revised COBA will more accurately reflect the benefits of the scheme and has been 

used for the purpose of this evaluation. 

4.5 To provide a re-evaluation of scheme benefits, the objective would be to introduce 

actual traffic volumes, rather than predicted traffic volumes, whereby the outturn 

traffic volumes are also input into the Do Minimum scenario. Although the benefits in 

the original COBA run and generally matched closely with the results in the POPE 

methodology, upon closer examination of the COBA network and forecast flows it 

was not possible to replicate this using the observed data primarily due to the way 

the input flows had been modelled and the fact that the COBA network used 

consisted of 200 links and therefore based upon the limited journey time and traffic 

flow data, accurately updating the network would not feasible. 

4.6 To enable a consistent comparison with the AST, the differing scheme opening years 

between the AST and the revised COBA need to be adjusted as the AST was based 

upon the scheme discounted back to 1994 and the revised COBA was based upon a 

the scheme discounted back to 1998. 


4-1



4.7 To enable a consistent comparison, the revised COBA was discounted back a further 

4 years to 1994. This would effectively lower the outturn benefits because the first 

year of benefits would be realised further in the future from the discounting base 

resulting in the first year of benefits being lower solely due to the benefits stream 

being further in the future. 

4.8 This process replicates the benefits from the COBA revision with the 2003 opening 

date and puts it in the context of the OPR AST enabling a direct comparison to be 

made between the revised COBA and the original OPR. Based on this adjustment, 

Table 4.1 shows the difference between the revised COBA and the original OPR 

publication. 

Benefit AST OPR (1994 

prices discounted 

to 1994) 

Revised COBA 

(1998 prices 

discounted to 

1998) 

Revised COBA 

(1994 prices 

discounted to 

1994) 

Journey Time and 

Vehicle Operating 

Cost 

£27.6m £34.56m £30.95m 

Accident Benefits £10.5m £10.30m £9.22m 

PVB £38.2m £44.86m £40.17m 

Table 4.1 – Comparison of OPR AST and Revised COBA analysis 

4.9 The revised COBA which was produced in 2001 for a 2003 opening when adjusted 

for a 1994 price and discounting base, estimated journey time savings to be 12% 

higher than in the original OPR AST and the accident savings to be 12% lower. The 

overall effect is a Present Value of Benefits (PVB) 5% higher than when the original 

OPR AST was produced. 

4.10 For the purpose of the comparison of the Appraisal Summary Table and Evaluation 

Summary Table in Chapter 5, it will also be necessary to convert the results from the 

POPE methodology using the same process. Vehicle operating costs have not been 

considered in the POPE evaluation as they are expected to be negligible and only 

account for 1% of PVB in the COBA analysis. Table 4.2 shows the revised POPE 

benefits for comparison with the original OPR AST benefits. 


4-2



Benefit AST OPR (1994 


to 1994) 

POPE 2003 

Scheme (1998 


to 1998) 

Revised POPE 

(1994 prices 

discounted to 

1994) 

Journey Time and 

Vehicle Operating 

Cost 

£27.6m £35.00m £31.34m 

Accident Benefits £10.5m £11.09m £9.93m 

PVB £38.2m £46.09m £41.27m 

Table 4.2 – Conversion of POPE Methodology Benefits for OPR AST Comparison 

RE-EVALUATION OF SCHEME COSTS 

4.11 As well as re-assessing the level of benefits accrued we have also undertaken a 

review of predicted and actual costs. Table 4.3 presents the predicted costs 

calculated before opening as part of the justification of the scheme, as well as the 

actual costs converted to the same price base so that direct comparisons can be 

made between them. Outturn prices have been converted from 2002 figures to 1994 

prices by using the change in RPI between 2002 and 1994 between which there was 

a 23% increase in prices. The prices are undiscounted total capital costs. 

Predicted (1994 

Prices) 

Outturn (2002 

Prices) 

Outturn (1994 

Prices) 

Construction N/A £30.19m £24.69m 

Land N/A £1.33m* £1.09m* 

Preparation N/A £0.48m £0.39m 

Supervision N/A £0.60m £0.49m 

TOTAL £30.9m £32.6m £26.7m 

* Does not include potential claim of £4.5m submitted under the Section 17 of the Land 

Compensation Act 


Table 4.3 – Predicted and Outturn Scheme Costs 

4.12 Subsequently the undiscounted total costs need to be adjusted to take into account 

the difference in period to base year discussed in the recalculation of the benefits. 

To again enable consistency, the Present Value of the outturn costs will be based 

upon the factor between undiscounted cost and discounted cost in the OPR. The 

comparison of OPR and Outturn costs shows that although the outturn costs are 

higher due to the later construction date, in economic terms the schemes outturn 

costs were lower than what was predicted. Should the claim under the Land 

Compensation Act be successful to the total £4.5m claim the undiscounted outturn 

costs in 1994 prices would be £30.3m which is still £0.6m less than what was 

specified at OPR stage. 

4.13 For the calculation of present value in the EST it was assumed that the expenditure 

profile of the outturn costs was similar to the profile in the revised COBA forecasts. 

4-3



5. Evaluation Summary Table 

INTRODUCTION 

5.1 In order to evaluate fully the effects of the opening of the bypass, we have 

undertaken a review of the Appraisal Summary Table (AST) prepared for each of the 

improvements. Table 5.1 presents the AST’s for the A6 Clapham bypass. 

5.2 These AST’s summarise the predicted impacts of the two schemes across a range of 

different sub-objectives. The sub-objectives considered within an AST are: 

 

 

 

 

 

Environmental impacts such as Noise, Local Air Quality, Landscape, 

Biodiversity, Heritage and Water; 

Safety impacts, measuring reduction in accidents; 

Economy impacts including savings in Journey time and Vehicle Operating 

Costs, Scheme Cost and Reliability of journeys; 

Accessibility impacts, such as change in access to public transport, severance 

within communities and impact on pedestrian and other modes; and 

Integration, measured by how the scheme accords with local policy. 

APPRAISAL SUMMARY TABLES (AST) 

5.3 The main points to note from the ASTs are: 

Environment: 

 

 

 

Safety 

Improvement due to vehicles re-routed away from village so that 301 properties 

would benefit from reduced noise in Clapham; 

Similarly, 400 properties would see an improvement in air quality; 

Negative impacts forecast on landscape, biodiversity and water 

Significant number of accidents saved, (311 accidents through Clapham over 30 

years); 

Economy 

 

 

 

The original AST showed 7% of all vehicles were HGV’s. 

Significant benefits from journey time savings. 

Moderate benefits in terms of improvements to journey reliability. 

Accessibility 

 

Large benefits to severance and ‘pedestrian modes’ forecast by statement of 

removal of 80% of traffic from Clapham village. 


5-1



Integration 

 

Positive benefit shown for as will integrate with other highway schemes, rail 

based park and ride; and local residential and commercial developments. 


5-2



Table 5.1 – AST for A6 Clapham Bypass 

A6 Clapham, Bedford (GOER) 1996 scheme - 5km D2 bypass Cost £30.9m 

PROBLEMS 

Poor safety and environment within Clapham (pop 3,200) where A6 carries up to 21,000 vpd (7% HGV). 300 residential properties + 2 schools front 

on to the road. Peak hour queuing occurs on length between village and northern outskirts of Bedford. 

OTHER OPTIONS 2 Pelican crossings already provided in village. Large scale traffic calming scheme would have unacceptable noise, air pollution and severance 

effects. Other options considered include reduced standard single carriageway bypass on proposed line; an eastern bypass and improved rail services 

to new Bedford North station with park and ride. All have inferior benefits. 

CRITERIA SUB-CRITERIA QUALITATIVE IMPACTS QUANTITATIVE MEASURE ASSESSMENT 

ENVIRONMENTAL Noise Properties within Clapham benefit from removal of traffic 

No. properties experiencing: 

301 properties 

IMPACT - Increase In Noise 15 

experience net 

- Decrease in noise 316 

decrease in noise 

CO2 Local air quality Removal of through taffic by bypass will improve air quality within Clapham 

No. properties experiencing: -409 PM10 

tonnes added -improved air quality 400 -2549 NO2 

0 - 2000 

- worse air quality 0 

Landscape Bypass partially within local areas of Great Landscape Value and would result in loss of 

- Slight -ve 

pasture land 

Biodiversity County Wildlife Site affected - Slight –ve 

Heritage No significant impacts. - Neutral 

Water 

Even with mitigation, there may still be a significant risk of polluting a sensitive 

- Moderate –ve 

watercourse and an aquifier used for public water supply during both construction and 

operation; and an impact on flood risk as the scheme is within a floodplain and bridges a 

river. 

SAFETY - Bypass reduces pedestrian/vehicle conflict in village and replaces a section of poor Accidents Deaths Serious Slight PVB £10.5m 

standard single carriageway. 311 9 94 359 54% of PVC 

ECONOMY Journey times & Faster journey times on new bypass 

Peak Interpeak PVB £27.6m 

VOCs 

4.6 mins 3.5 mins 

Cost PVC £19.6m 

Reliability Route Stress Slight 

Before 104% After 38% Low rel to PVC 

Regeneration Serves regeneration priority area? No 

ACCESSIBILITY Public Transport Will help to reduce peak journey times of existing local bus services - Slight +ve 

Severance Removes 80% of traffic from village - Moderate +ve 

Pedestrian/other Will improve accessibility for residents to local services Moderate +ve 

INTEGRATION - Complements Bedford/Kempston package proposals and facilitates proposed Bedford 

North rail station with park and ride. Assists proposed local residential and commercial 

developments 

- Positive 

COBA PVB £38.2m PVC £19.6m NPV £18.5m BCR 1.95 


5-3



OUTTURN EFFECTS 

5.4 In order to assess the actual or outturn effects of the opening of the two 

improvement schemes, we have produced an Evaluation Summary Table (EST), 

which mirrors the appearance of the AST, and includes details of the actual subobjectives 

that have been evaluated. 

5.5 The POPE process concentrates on economy and safety impacts of new 

schemes at present, but this may be widened to include environmental effects, 

and guidance is currently being written to outline the best approach for these 

objectives at present. 

5.6 The main points to note on the EST are: 

Environment 

5.7 The environmental aspects of the schemes have not been evaluated in detail. 

The main premise for the benefits identified in the AST is that properties along 

the old A6 will experience a benefit in noise and air quality due to the removal of 

traffic onto the bypasses, and as the traffic reductions in the villages are similar 

to what was predicted, it is fair to say that the environmental impacts reported in 

the AST are likely to have been achieved. 

5.8 In terms of negative forecasts such as landscape, Biodiversity and water, no 

assessment of these sub-objectives have been carried out at present. 

Safety 

5.9 The AST predicted significant accident savings of 311 over the 30 year period. In 

order to evaluate whether these predicted savings are likely we have undertaken 

an initial evaluation of accident savings accrued for the new schemes. 

5.10 Normally, it is usual for accident savings to be evaluated at least three years after 

opening in order to get a fair reflection in the number of accidents in the corridor, 

therefore this evaluation for the One Year After Evaluation is an initial view and 

cannot be considered as a firm conclusion at this time. 

5.11 Despite this caveat, we have obtained accident data for three years before 

opening to determine an average annual number of accidents on the A6 between 

the Northern access/egress of the bypass onto the A6 and the junction with Cut 

Throat Lane and a year post scheme opening between the same two points split 

between accidents on the old A6 and on the A6 bypass. Average flows for the old 

A6 have been derived from the counts at Milton Ernest and South of Green Lane 

on the old A6. Table 5.2 shows the accident rates on the old A6 in the year 

before the bypass. Average flows on the bypass have been derived from the 

counts between the South Roundabout and the Oakley Road slip. Table 5.3 

shows the accidents split by bypass and old A6 based upon 3 years of ‘Before’ 

data and one year of ‘After’ data. 


5-4



Length of studied 

section (km) 

Average Flow 

(AADT) 

Average No of 

accidents 

Accident Rate 

(PIA/ mvkm) 

4.7 17,300 13 0.44 

Table 5.2 – Summary of Accidents on the A6 One Year Before 

Length of 

studied 

section(km) 

Average Flow 

(AADT) 

No of 

accidents 

Accident Rate 

(PIA/ mvkm) 

Old A6 4.7 4,800 2 0.24 

A6 Bypass 4.7 16,143 4 0.14 

Total Corridor 4.7 20,943 6 0.17 

Table 5.3 – Summary of Accidents on the old A6 and Bypass One Year After 

5.12 The accident rate along the A6 corridor through Clapham dropped from 0.44 

personal injury accidents (PIA) per million vehicle kilometres (mvkm) to 0.17 

PIA/mvkm, a drop of 61%. This includes a drop of 45% in PIAs per mvkm along 

the A6 through Clapham village. 

5.13 Table 5.4 shows the accidents by severity split. 

Number of Casualties 

Number of 

PIA’s 

Slight Serious Fatal 

Before 13 18 2 0 

After 6 8 6 0 

Table 5.4 – Accident Severity Splits Before And After 

5.14 Although the annual number of accidents has shown a decrease one year after 

opening, Table 5.4 shows a threefold increase in serious injuries one year after 

opening compared to one year before opening. This is solely due to a head on 

collision between two cars on the old A6 due to one of the cars speeding on a 

bend and moving across to the opposite side of the road and subsequently 5 

serious injuries occurred in this one single accident alone. 

5.15 Although the number of accidents has decreased since the opening of the 

bypass, the actual monetary cost of the accidents one year after study would 

exceed that before solely due to this one accident as the value of a serious injury 

is valued approximately 10 times higher than a slight accident. Analysis of 

accident figures back to 1999 on the A6 through Clapham indicates that this 

accident is ‘unusual’ with only one accident between 1999 and the opening of the 


5-5



bypass having more than one person seriously injured which was an accident 

with 3 serious injuries. Removal of these 5 serious accidents reveals an 

approximately constant severity split per accident before and after the opening of 

the bypass. Therefore, as in the POPE methodology it has been assumed no 

change in the cost of an individual accident at the one year after stage in the 

calculation of economic benefits. 

5.16 It is important to reiterate that this is a One Year Evaluation, and firm conclusions 

should really not be derived until at least three years after opening, but the initial 

signs are that the scheme has been successful in reducing accidents on the A6 

through Clapham. 

5.17 Atkins has obtained the locations of the observed accidents, and Figure 5.1 

shows the location of these accidents in 2002 one year before the scheme 

opened and Figure 5.2 shows the location of accidents in 2003, one year after 

the scheme had been open. This clearly indicates a reduction in the number of 

accidents along this corridor. 

5.18 Figure 5.2 shows that the four accidents on the bypass in the opening year were 

at separate locations with three on the main carriageway and one on the 

approach to the new southern roundabout. The carriageway accidents comprised 

of two collisions with the central barrier attempting to avoid a collision with 

vehicles in front, one of which subsequently hit the vehicle in front after hitting the 

barrier; and one accident due to the driver losing control of the vehicle and 

colliding with barriers both sides and rolling over. The remaining accident on the 

southern roundabout was due to a car driver cutting across into the right hand 

lane on the entry to the roundabout and hitting a motorcyclist. 


5-6



Figure 5.1 – Accidents One Year Before the Opening of the A6 Clapham Bypass 


5-7



Figure 5.2 – Accidents One Year After the Opening of the A6 Clapham Bypass 

5.19 Within the AST the predicted accident savings over the 30 Year assessment 

period have been reported and in order to provide an initial view on the 

robustness of these conclusions we have predicted the numbers of accidents 

over the 30 Year assessment period. 

5.20 One issue regarding the AST is that although the benefits between the original 

AST OPR and the revised COBA were similar in monetary terms, the number of 


5-8



accidents forecast to be saved in the OPR AST is 311 whilst this is subsequently 

lowered to 245 in the revised COBA. Based on the annual to 30 Year factors 

derived from the revised COBA, the actual observed annual accident saving of 7 

per annum equates to 220 accidents saved over the 30 Year Period on the 

bypassed links. The reason why this figure is lower which contradicts with the 

fact that we have reported higher than forecast accident benefits in Chapter 3 is 

that the 245 accident savings is based upon the entire modelled network within 

COBA whereas the POPE analysis compared the actual and modelled accident 

savings on just the bypass and bypassed section of the A6. In practice there will 

be some benefits on other roads due to reduced traffic. Whereas the complete 

COBA analysis will have forecast benefits due to the reduction of traffic on other 

roads (e.g. on roads through Oakley village), the POPE analysis only considers 

accident reduction on the bypass and the old A6. 

Accessibility Impacts 

5.21 The AST predicted that accessibility benefits would accrue in terms of reduced 

severance and improved conditions for pedestrians and other modes, and these 

would result in an 80% reduction in traffic in the village. 

5.22 Outturn traffic volumes suggest that 60-75% of the Clapham through traffic was 

removed from the village suggesting that the accessibility benefits outlined in the 

EST are moderate. 

Integration 

5.23 The bypass complements the A421 Bedford bypass and based on proposed 

future developments, it will also complement the proposed Bedford Western 

bypass which would link the A6 Bypass to the A421 which is planned in 2007/08. 

Plans also exist for a possible Park and Ride site near the Clapham bypass. 

Summary 

5.24 A summary of effects across all evaluation sub-objectives are included in the 

EST in Table 5.5. 


5-9



Table 5.5 – EST for A6 Clapham Bypass 

A6 Clapham, Bedford (GOER) 2002 scheme - 5km D2 bypass Cost £26.7m 

PROBLEMS 

SOLVED 

Indication of reduction in traffic flows on the A6 through Clapham from between 15,000 - 23,000 vehicles per day to 2,000 – 8,.500 vpd. Proportion of 

HGV’s using A6 through Clapham reduced from 8% to 2%. 

OTHER OPTIONS Not assessed 

. 

CRITERIA SUB-CRITERIA QUALITATIVE IMPACTS QUANTITATIVE MEASURE ASSESSMENT 

ENVIRONMENTAL Noise 

No assessment specifically made – but AST conclusions are likely to be valid as traffic 

- Large +ve 

IMPACT 

volumes have been significantly reduced in village 

Local air quality 

No assessment specifically made – but AST conclusions are likely to be valid as traffic 

volumes have been significantly reduced in village 

Large +ve 

Landscape Not assessed - 

Biodiversity Not assessed - 

Heritage No assessment specifically made – unlikely to be significant impacts. - - 

Water 

Not assessed - - 

SAFETY - Bypass reduces pedestrian/vehicle conflict in village and replaces a section of poor 

Accidents Saved PVB £9.9m 

standard single carriageway. 220 

ECONOMY Journey times & Faster journey times on new bypass 

Peak Interpeak PVB £31.3m 

VOCs 

5 mins 4.5 mins 

Cost PVC £18.4m 

Reliability Route Stress Slight 

Before 79% After 28% Low rel to PVC 

Regeneration Not assessed - - 

ACCESSIBILITY Public Transport Not assessed - - 

Severance 60-75% of traffic has been removed from the village, thus greatly reducing the 

severance. 

- Moderate +ve 

Pedestrian/other 

INTEGRATION - 

60-75% of traffic has been removed from the village, thus greatly improved the 

environment for pedestrians and others. 

Moderate +ve 

COBA PVB £41.3m PVC £18.4m NPV £22.9m BCR 2.24 


5-10



6. Summary of Conclusions 

6.1 The Highways Agency has a requirement to carry out re-evaluations of trunk road 

schemes recently implemented by the Department of Transport. The purpose of 

these re-evaluations is to provide a back check of the levels of benefit accruing 

from new schemes and to determine how far the department achieves the 

objectives and benefits it claims from its road programme. 

6.2 In summary, the main points to note from the One Year Evaluation of the A6 

Clapham Bypass TPI Scheme are; 

Before the improvements scheme the old A6 route through the village of 

Clapham carried around 15,000 – 23,000 vehicles per day (on an average 

weekday); 

The A6 Clapham Bypass, which officially opened on 12 th December 2002, 

carried around 17,000 vehicles per day, a month after opening; 

A year later, the traffic volumes on the bypass has grown to around 18,500 

vpd; 

 

75% of traffic has been removed from the bypassed section of old A6 in 

Clapham suggesting that the schemes have been successful in removing 

through traffic from the village; 

The OPR AST predicted a total benefit of £38.2m comprising of £27.6m 

journey time and VOC savings with £10.5m of accident savings in 1994 

prices discounted to 1994. The POPE methodology produced total benefits 

of £41.3m comprising of £31.3m journey time savings and £9.9m of accident 

savings in 1994 prices discounted to 1994. 

Journey time information suggests that time savings of between 2 to 3 

minutes are being forecast for journeys along the 5km length of the bypass 

compared to the corresponding route along the A6 through Clapham. 

 

 

 

 

The completion of the A6 has led to a reassignment of traffic onto the road 

and new trips, and the benefits from these trips have not been incorporated 

as the POPE methodology. 

The predicted scheme costs for the A6 Clapham bypass were estimated to 

be £30.9m in 1994 prices. This outturn costs were £27.7m in 1994 prices 

although this could increase as there are still Land Compensation Act claims 

outstanding. 

An Evaluation Summary Table has been prepared to be directly compared 

with the AST’s prepared before opening. These show that the prediction of 

the relief of traffic in Clapham was robust and that the accident savings 

predicted were robust. 

The A6 Clapham Bypass has led to a reduction in the number of accidents in 

the corridor, where up to 7 personal injury accidents have been saved in the 

first year after opening. 

6.3 Evaluation of other sub-objectives within the AST will be carried out as part of the 

Five-Year After assessment, which will consider accident reductions in more 


6-1



detail, as well as how land use has changed in the area as a result of the A6 

Clapham Bypass. 


6-2

One Year After Study: A6 Clapham Bypass

Create successful ePaper yourself

Delete template?

Save as template?