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Chocolate Poodle Railway Bridge Feasibility Study – Advance Signing

Options Report

1029551/R/001

November 2010

For Wiltshire Council

Prepared by Jamie Adkins Derby Court Epsom Square Epsom Road White Horse Business Park Trowbridge Wiltshire

BA14 0XG T 01225 756 600 F 01225 756 611

E Jamie. Adkins@mouchel.com

Location

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Document Control Sheet

Project Title Chocolate Poodle Railway Bridge

Report Title Feasibility Study –Advance Signing Options Report

Report Reference 1029551/R/001

Version A

Issue Date 3rd

November 2010

Record of Issue

Version Status Author & Date Checked & Date Authorised & Date

A Issue Jamie Adkins

November 3rd 2010

David Swann

November 3rd 2010

Simon Burgess

November 3rd 2010

Distribution

Organisation Contact Format Copies

Wiltshire Council Peter Binley E,P 1

Wiltshire Council Julian Haines E,P 1

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Contents

1 Introduction .......................................................................................................... 1

1.1 Background ................................................................................................ 1

1.2 Location Plan.............................................................................................. 2

1.3 Scheme Overview ...................................................................................... 2

2 Desk Study .......................................................................................................... 3

2.1 Methodology............................................................................................... 3

2.2 Sources of Information................................................................................ 3

2.3 Existing route – A360 between Devizes & the A303 ................................... 4

2.4 Alternative routes for HGV’s exceeding 13’ 6’’ ............................................ 6

3 Design Options....................................................................................................... 7

3.1 Option 1 - Western route using the A361, A350, A36 and A303 ................. 7

3.2 Option 2 - Eastern route using the A342, A345 and A303........................... 9

4 Summary ........................................................................................................ 12

4.1 Route distance ......................................................................................... 12

4.2 Traffic counts............................................................................................ 12

4.3 Structures................................................................................................. 12

4.4 Traffic Orders and signing requirements................................................... 12

4.5 Conclusion................................................................................................ 13

Appendix A ........................................................................................................ 14

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1 Introduction

1.1 Background

Chocolate Poodle Bridge is a single span structure carrying the twin track Stert

to Westbury (SWY) rail line over the A360 at Littleton Panell. The bridge has a

measured head room of 14’ 0’’ and signed headroom of 13’ 6’’.

Standard headroom to be maintained on the national highway network is 16’ 6’’,

to allow free passage of high vehicles. Restrictions below this height have to be

signed to indicate the maximum safe height of vehicles able to pass under the

bridge; the signed height should be between 3’’ and 6’’ below the actual height

to allow for slight bouncing of vehicles and inaccuracies in the road surface.

In 2004 Network Rail expressed concern about the number of over height

vehicles colliding with the bridge deck and subsequently installed a Collision

Protection Beam.

Ringway Parkman undertook a headroom survey in January 2005; on receipt of

this information the Wiltshire Council arranged to sign the bridge at 13’ 6’’.

Heavy Goods Vehicles (HGV’s) exceeding the signed height are diverted

around the low structure via the network of adjacent minor roads through Great

Cheverell (Ref to 1.2 – Location plan).

Cheverell Magna Parish Council have complained about an increase in HGV

traffic through their village and have asked Wiltshire Council to investigate the

matter to see if measures could be put in place to reduce the volume.

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1.2 Location Plan

1.3 Scheme Overview

Wiltshire Council instructed Mouchel to provide two feasibility reports:-

a) Advance Signing Options Report

A study of alternative routes for HGV’s (Exceeding 13’ 6’’ in height) to

travel between Devizes and the A303, avoiding the A360 and the

diversion route through Great Cheverell. This report reviews signing

requirements and suitability of alternative routes.

b) Carriageway Lowering Options Report

A study investigating the construction requirements and cost

implications of lowering the carriageway under Chocolate Poodle

Railway Bridge.

This report provides a summary of advance signing options; Refer to

1029551/R/002 for the carriageway lowering options report.

Chocolate Poodle

Railway Bridge

A360 Salisbury

A360 Devizes

Diversion route for HGV’s,

through Great Cheverell -

Avoiding low bridge

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2 Desk Study

2.1 Methodology

The following items were reviewed to identify viable alternative routes for

vehicles exceeding 13’ 6’’: -

• Traffic Orders along routes leading to or from the A360, restricting

vehicles by weight, height and width.

• A list of ‘A class’ roads providing an alternative route to the east and

west of the A360.

• Locations and details of existing signs at the north and south of the

existing route.

• Structures along the alternative routes for appropriate loading capacity

(40 tonnes) and geometry (headroom (16’ 6’’ (5.03m + sag curve

radius), and width to TD27/05).

• Total distance of route.

• HGV traffic counts and analysis to identify the requirement for diversion

of high vehicles.

2.2 Sources of Information

Table 1: Details of all Sources Used to obtain relevant Information

Information Type Title / Source

Existing Signs and Route Information Site Survey

Traffic Data Devizes Traffic Counts undertaken in March 2006; 12 hour AADT.

TRL PR T 079/04 – 3.3 – Measures to Reduce the Frequency of Over-Height Vehicles Striking Bridges’ : -

- Data from this report has been used for HGV height distribution data.

Bridges Information Yellow Files – Wiltshire Structures Team / Network Rail.

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2.3 Existing route – A360 between Devizes & the A303

2.3.1 Location Plan

2.3.2 Route distance

The existing route distance for vehicles exceeding 13’ 6’’ is 18.9 miles long

(including the diversion through Great Cheverell).

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2.3.3 Devizes Traffic Count 2006

Destinations /

Directions of traffic

Total Number of

Vehicles (12 Hour

AADT)

Total no. of HGV’s HGV’s with a height

exceeding 13‘6’’

Devizes � Potterne

(A360 South)

3687 109 21

Potterne � Devizes

(A360 North)

3877 160 30

Two Way 7574

269 51

Notes: -

1. The total number of HGV’s has been distributed by height to TRL

report PR T/079/04, 3.3. The percentage of HGV’s equal to or

exceeding 13’ 6’’ = 18.6%

2. It is assumed that all HGV’s equal to or exceeding 13’ 6’’ use the

signed diversion route through Great Cheverell.

3. Count data is taken from the nearest available site in Potterne, this is

2.4 miles north of Chocolate Poodle Bridge. Adjacent minor roads have

traffic orders restricting HGV’s, except the B3098 Westbury to West

Lavington.

4. For the purpose of this report it has been assumed that the origin and

destination for all HGV’s listed in the count data is between Devizes

and the A360 / A303 junction near Winterbourne Stoke.

5. A classified traffic count for the A360, the diversion route through Great

Cheverell and adjoining roads would improve the accuracy of the count

data.

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2.3.4 Traffic Orders & Existing signs

a) Weight limit restrictions

• Traffic orders and signs along routes leading to or from the A360,

restricting vehicles by weight, are shown on drawing 1029551-D-002.

b) Height limit restrictions

• Traffic orders restricting vehicles by height are located prior to the

diversion route (Refer to 1.2).

• There are signs providing advance warning of the restricted headroom

structure (Chocolate Poodle), located in Devizes (Approximately 4

miles north of Chocolate Poodle)

• There are no advance warning signs of the restricted headroom

structure (Chocolate Poodle) located at the A303 / A360 junction

(Approximately 5 miles south of Chocolate Poodle)

• There are no advance alternative routes for vehicles exceeding 13’ 6’’

located in Devizes or at the A303 / A360 junction.

c) Existing height restriction signs:-

i) Warning signs on approach to low bridge – Southbound approach:-

There is another height restriction sign mounted on the bridge deck soffit on the

northbound approach. There are advance warning height restriction signs 100

yards prior to the structure on the northbound and southbound approach.

2.4 Alternative routes for HGV’s exceeding 13’ 6’’

There are two alternative routes using A class roads:-

a) Option 1 - Western route using the A361, A350, A36 and A303

b) Option 2 – Eastern route using the A342, A345 and A303.

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3 Design Options

3.1 Option 1 - Western route using the A361, A350, A36 and A303

3.1.1 Location plan

3.1.2 Route distance

Option 1 diverts high vehicles to the west of the existing route. The diversion

route is listed below:-

- Devizes along the A361

- Joins the A350 southbound at Semington

- Through Westbury and joins the A36 southbound

- Joins the A303 eastbound at Wyle.

This route is 36.1 miles long. This is an increased distance of 17.2 miles.

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3.1.3 Traffic Counts

The western diversion route for high vehicles is a Wiltshire County Primary and

Trunk Road route.

The anticipated increase in volume is 21 HGV’s southbound and 30 HGV’s

northbound during a 12 hour weekday period between 7am and 7pm; this will

not have a significant impact on existing road / junction capacity.

3.1.4 Traffic Orders and Signing requirements

Additional signing would be required in Devizes, Westbury and all major

junctions along the A350, A36 and A303.

3.1.5 Structures

Structures along this route do not restrict HGV traffic by weight, height or width.

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3.2 Option 2 - Eastern route using the A342, A345 and A303

3.2.1 Location Plan

3.2.2 Route distance

Option 2 diverts high vehicles to the east of the existing route. The diversion

route is listed below:-

- Devizes along the A342

- Join the A345 southbound at Rushall

- Join the A303 westbound at Amesbury.

This route is 21.9 miles long. This is an increased distance of 3 miles.

X

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3.2.3 Traffic Counts

Destinations

/ Directions

of traffic

Existing

Number of

Vehicles (12

Hour AADT)

Existing

Total no. of

HGVs

Additional

HGV’s

Estimated

total

Vehicles

using

Eastern

diversion

route

Estimated

total HGV’s

using

Eastern

diversion

route

Devizes �

Rushall

(A342 East)

3342 154 21 3363 175

Rushall �

Devizes

(A342 West)

3480 181 30 3510 211

Two Way 6822 335 51 6873 386

• Refer to 2.3.3 for calculation of additional HGV’s.

• There is a 15% estimated increase in HGV’s along the eastern

diversion route.

• There is an estimated 1.3% increase in all vehicles along the eastern

diversion route.

• The additional volume of HGV’s using the eastern diversion route will

not have a significant impact on road / junction capacity.

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3.2.4 Traffic orders and signing requirements

Additional signing would be required in Devizes, the A342 / A345 junction and

the A345 / A303 junction.

A preliminary sign layout is shown on drawing 1029551-1200-001.

The principle is to introduce a minimum number of new signs around the control

locations (A & B) in order to guide target vehicles along the alternative route.

The preliminary design layout includes the following sign types:-

- Miscellaneous Informatory signs

- Alternative route direction/trigger signs,

- A series of small symbol signs at all major junctions along the alternative

route.

There are numerous direction signs along the A303 including Off Network

Diversion Route (ONDR) signs; these must be considered when specifying the

use of diversion route symbols to ensure clarity of each diversion route and

prevent conflicting symbols.

3.2.5 Structures

The structure known as ‘The Clock’ is a narrow road bridging over the railway

line (Ref 3.2.1 at the location marked with X).

There are currently no traffic orders by weight, height or width; an advisory

‘Road Narrows’ sign warns of the restricted width on the structure.

A more detailed review of the geometry and two way traffic flow is

recommended.

The structure is rated at a capacity of 40 tonnes, which meets current standards

for ‘A class’ roads.

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4 Summary

4.1 Route distance

Route Estimated Travel Distance

Existing A360 Route 18.9 miles

Option 1 (Western route) 36.1 miles

Option 2 (Eastern route) 21.9 miles

Option 1 is not a viable due to the significant increase in distance, therefore it

has been discounted.

Option 2 shows a minor increase in distance and is seen as a viable solution on

this basis.

4.2 Traffic counts

There is a 1.3% estimated increase in total vehicles from 7am to 7pm. The

additional volume of HGV’s using the eastern diversion route will not have a

significant impact on road / junction capacity.

4.3 Structures

The structure known as ‘The Clock’ is too narrow to allow two way HGV’s, it is

recommended that a review of existing geometry, traffic flows and priority is

undertaken prior to any diversion signing for HGV’s.

4.4 Traffic Orders and signing requirements

Refer to drawing 1029551-1200-001. To provide an appropriate signing layout

for eastern diversion route signs would need to be erected along the A303,

Approval from the Highways Agency Area 2 would be required.

Signs on the A303 may be subject to a reduction in size due to the proximity of

Stonehenge.

The proposal at Airman’s corner (south of Stonehenge), undertaken by Halcrow

on behalf of English Heritage, should be considered prior to any diversion

signing scheme. The scheme is currently on-hold.

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4.5 Conclusion

The diversion route to the east of the A360 is a viable solution to divert vehicles

exceeding 13’ 6’’, and reduce the flow of heavy goods vehicles through Great

Cheverell.

Traffic flows, accident data and geometry at the structure known as ‘The Clock’

should be reviewed prior to any diversion signing scheme.

It should be noted that Satellite Navigation systems can lead motorists to

unsuitable routes; reliance by many drivers on such systems reduces the

benefits of any signing scheme.

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Appendix A Scheme drawings:-

1029551-D001 Alternative Diversion Route – Layout Plan

1029551-D002 Existing Weight Limits

1029551-1200-001 Diversion Route for vehicles exceeding 13’ 6’’

– Sign Layout & Details