Highways Agency

Safe roads, Reliable journeys, Informed travellers

1 Introduction

Feasibility Study

1 Introduction

1.1 Objectives

1.1.1 The objective of the study is to investigate the feasibility of providing a bridge crossingat the Black Swan Crossroads on the A19 Trunk Road. Sufficient design work is to bedone in order to enable the Highways Agency Route Manager to decide whether thereis a robust case for a scheme to be included in the forward programme.

1.1.2 The study will include consideration of junction and bridge options; production of ascheme design shown on a layout plan and longitudinal section; a bridge generalarrangement drawings, costs, economic assessment using COBA and a Short ProjectAssessment Report (PAR).

1.2 Background

1.2.1 The Black Swan Crossroads on the A19 is located about five kilometres south of theA19/A67 junction near Crathorne and is shown labelled "The Site" on Figure 1. Theside roads at the Black Swan Crossroads lead to The Rountons to the west and HuttonRudby to the northeast. This junction has been the subject of several improvementschemes in recent years with the aim of improving safety. The latest of these schemeswas carried out in the summer of 2002 and its aim was to improve the visibility forvehicles waiting in the central reserve.

1.2.2 In July 2004 the Highways Agency stopped up the central reserve gap at the junctionusing an experimental order that lasts until 16th January 2006. The order also includesbanning 'U' turns at the remaining central reserve gaps between Crathorne and TontineJunctions. The at-grade crossroads has been closed to crossing and right turning trafficby blocking up the central reserve opening. A decision will need to be made by HAwhether to extend the order or re-open the central reserve gap. There has been localopposition to the gap closure and the Highways Agency has agreed to look at thepossibility of providing a bridge at this location to cover all turning movements.

1.3 Information Provided

1.3.1 A copy of an earlier report by Halcrow entitled "Area 18 Motorway and Trunk roadsDurham and North, East and West Yorkshire A19 (T) Crathorne to Tontine Safety StudySupplementary Report December 2002" (Ref 1) has been made available to the studyteam and provides useful data on the A19 and local roads in the vicinity of the BlackSwan junction, including traffic survey and assessment results.

1.3.2 The Highways Agency also provided Ordnance Survey digital mapping at 1:2500 scaleaccuracy, covering the Black Swan junction and surrounding area. Landform digitalcontours were also obtained through the Highways Agency's Pan-governmentarrangement with Ordnance Survey.

1.3.3 Ground level photographs of the junction were provided and these were supplementedby the study team during the site visit on 5 January 2005. At the request of theHighways Agency, no contact or enquiries were made to utilities companies, statutoryauthorities or landowners.

1.3.4 Following discussions with Highways Agency's Traffic and Economics Team (TAME) itwas agreed that the economics would be assessed using the latest version of COBA,v11.6 and that the PAR would be the short version. The latest issue of PAR (Version3.3) and its guidance notes were provided to the study team.

1.3.5 As-built and record drawings were also provided to the study team by Autolink Ltd (A19concessionaires) covering highway drainage, street lighting and utilities. Wherepossible this information was supplemented by observation from within the highwayboundary during the site visit by the study team on 5 January 2005.

1.4 Output Required

1.4.1 Output from the study comprises a completed PAR with relevant worksheets and othersupporting information; cost justification and supporting information and generalarrangement drawings of bridge options. Supporting information will include schemelayout plans and longitudinal sections of the proposed junction layouts, site locationplan and COBA results.

2 Highway Design and Layout

Feasibility Study

2 Highway Design and Layout

2.1 Existing Junction

2.1.1 The existing junction at the Black Swan Crossroads with the central reserve gap closedis operating as a left-in/left-out junction onto each carriageway of the A19 Trunk Road.The left-in/left-out carriageway areas of the existing junction have corner radii ofapproximately 15m and are defined by means of road markings, bollards and signing tochannel traffic into and out of the junctions. Acceleration and deceleration splays areprovided on the A19 and appear to have dimensions meeting the criteria in DMRBTD20/82 (now superseded by TD 42/95). This existing layout is similar to that set out inDMRB TD40/94 for compact grade separation, but without kerbs on the splitter islandsand with acceleration and deceleration splays on the A19 carriageways that are longerand wider than in that standard. During the consideration of the type of junction thatmay be suitable, the possibility of retaining these in their present form and incorporatingthem into the proposed junction was kept in mind.

2.2 Junction Options

2.2.1 The traffic flows and turning data for the junction, based on flows from the Halcrowreport Ref.1), indicate that due to relatively low flows on the side roads (1150 AADT in2022, the assumed design year) and an A19 flow of 37500 AADT in 2022 lead to theconclusion that an appropriate form of junction would be Compact Grade Separation inaccordance with TD40. This standard advises that compact grade separation can beeconomically justified down to mainline flows of around 12,500 AADT and is suitable foruse where mainline flows are between approximately 12,500 and 30,000 AADT andside road flows are below 10% of that on the mainline. At the Black Swan, the mainlineflows are currently about 28,200 AADT and are forecast to be about 37,500 AADT in2022 with side road flows forecast at about 1150 AADT. Although in the design yearthe mainline flow is forecast to be greater than 30,000 AADT, the side road flow is onlyabout 3% of the mainline flow. Also a compact grade-separated junction at the BlackSwan is in keeping with the A19 standards that include a mixture of at-grade and gradeseparatedjunctions.

2.2.2 The standard defines various different layouts for compact grade separation. Most ofthese allow for the side road to be continuous with connecting loops between the sideroad and the main line, the loops joining the side road at a simple T-junction. Thedesign speed required for the side road would normally be around 85 km/h.

2.2.3 The alternative is for the side road to be discontinuous so that the section crossing themain line on a bridge forms the loop. This has the disbenefit that through traffic on theside road has to negotiate two T-junctions with their associated delays. However, thestandard does allow for the loop to be designed to a 30 km/h design speed sopermitting vertical radius curves smaller than with a straight through side road. Thesmaller radius vertical curves allow the loop road to be shorter with consequent savingsin cost.

2.2.4 The existing side road originally formed a cross roads with the A19 with no staggeringof the side road connections to the A19. The loop arrangement described in theprevious paragraph readily adds to the current layout to form a compact gradeseparation while retaining most of the existing side road and the acceleration anddeceleration splays on the A19 main line. Being able to keep and incorporate thesesections of existing road into the proposed junction has benefits in less constructioncost; less adverse affect on adjacent property and access; less effect on public utilitiesand less disruption during construction. In view of the existing junction layout and thebenefits of a lower design speed for the loop, this arrangement was selected for takingforward in the feasibility study.

2.3 Junction Location

2.3.1 Having decided on the compact grade separation junction layout type, it was necessaryto consider whether the loop should be positioned on the north or south side of theexisting side road. Matters taken into consideration were topography, drainage, thewatercourse Trenholme Stell/East Rounton Stell, services, field boundaries and landuse.

2.3.2 The topography in the vicinity of the junction is relatively flat. In the north/southdirection the land slopes at a gradient of about 1 in 100 towards the south and in theeast/west direction the land slopes upwards in each direction from the A19 at a gradientof about 1 in 100. To the south of the existing side road and parallel to it there is theStell. As the proposed loop road would have to rise up about seven metres from thelevel of the existing side road to cross over the A19, the slightly higher ground to thenorth would require less earthworks to form the bridge approach embankments thanwould be needed on the south side of the existing road where the ground level is lower.If the loop were to be sited on the south side of the existing road it would be close to theStell. Sub-soil conditions close to the watercourse may be less favourable from anengineering point of view for embankment construction than that on the north side.Also, placing an embankment close to the watercourse could have adverse effects onthe local water regime if the embankment encroached into the flood plain. On the basisof these criteria, placing the loop on the north side is more favourable. A disadvantageof the north side is that the loop would cut through an area of woodland but this appearsfrom inspection to be relatively recent planting and could be mitigated by new plantingas part of the improvement scheme. However, overall it is considered preferable tolocate the loop on the north side and this has been taken forward for the study.

2.4 Services

2.4.1 From information provided by the HA and their agents, from OS mapping and fromobservation on the site visit, the approximate locations of utilities services, highwaydrainage and highway lighting was obtained. Most of the services are in or close to theexisting roads. Those that run alongside the A19 would be affected by the proposedside road embankment and would be likely to need protection or sleeving where theypassed beneath the embankment. This protection or sleeving would be needed tosome extent, regardless of whether the loop is located on the north or south side of theexisting side road. There is an overhead electricity supply line running from northeastto southwest that carries a supply to the Black Swan public house. This overhead lineis affected by the loop on the north side, requiring relocation of one or possibly twopoles. On the basis of these criteria, the advantages of locating the loop to the north orsouth are neutral apart from the overhead line, which would favour the south. However,this is not considered an over-riding matter, as it may be possible to avoid the affectedpole by adjustments to the design at a later stage.

2.5 Design Standards

2.5.1 Highway design standards are in accordance with the Highways Agency's DesignManual for Roads and Bridges (DMRB) (Ref 2) and in particular DMRB Volume 6Section 2 Part 5, TD 40/94 Layout of Compact Grade Separated Junctions. Twooptions for the junction layout have been designed.

2.5.2 Option 1, shown on the scheme layout drawing Figure 2, uses the desirable minimumstandards and includes 5% gradients on the bridge approaches. The requirements ofTD40/94 in terms of gradient are that the needs of cyclists and the risk of icy conditionsshould be considered. For cyclists the standard says that gradients should be limited to5%. The Halcrow report (Ref 1) indicates that some cyclists would use the bridge andat the time of the survey in July 2002 the number was 13 in the 12 hour study period.With a bridge in place the number of cyclists that would use it to get from one side ofthe A19 to the other may well increase firstly due to the grade separation being a saferroute compared with the at-grade crossing and secondly due to the trend towardsgreater use of cycles. Cycling and the provision of cycling facilities are also encouragedby government policy.

2.5.3 The need for the use of gradients of 5% would need to be assessed in more detailshould the scheme proceed. Surveys and investigation of potential cyclist use of thescheme and local authority policy relating to cycling would be needed. The localclimatic conditions would need to be investigated to determine frequency and severity ofroad icing.

2.5.4 Option 2, shown on scheme layout drawing Figure 3, makes use of the relaxations ofstandards permitted by TD40/94, relating to horizontal and vertical alignment radii. Thisoption also incorporates bridge approach gradients of 8%, which is to desirableminimum standard, subject to considerations of cyclists' usage and road icing asdescribed above. The benefits of applying relaxations of standards are mainly relatedto the length of the loop being shorter than with Option 1, which results in lessconstruction cost and a better result in the economic assessment. There would be asmall reduction in level of service with Option 2 compared with Option 1 due to thesmaller radius curves and the steeper gradient. These same factors could also havesome effects on safety, which would be considered during safety audits and dealt within subsequent design.

2.5.5 In both options it has been assumed that the existing junction layout within the trunkroad can be incorporated into the compact grade separated junction with nomodifications to carriageway pavement. The existing left-in/left-out junctions betweenthe side roads and the A19 and the acceleration and deceleration splays would beretained along with the recent works to close the central reserve gap. Allowance hasbeen made in the cost estimates for modifications to road markings and signing toprovide for side road traffic's safe entry to and exit from the A19. This aspect of thedesign would need to be reviewed should the scheme proceed to ensure that the layouteither complies fully with TD40/94 or that departure from standards is obtained. In anyevent, this part of the layout should be considered in the safety audits.

2.5.6 The lane width for the loop, or compact connector road, selected from TD 40/94 Table6/4 is 3 metres, giving a carriageway width of 6.6 metres including central hatching butwith widening on horizontal curves in accordance with Table 6/3. Road widths onsections of existing road that are incorporated into the scheme remain unaltered.

2.6 Drainage

2.6.1 Both options would produce an increase in surface water run-off due to the increase inpaved area in the junction. Run-off retention and pollution control is likely to be neededprior to the existing highway drainage system or other outfall. Allowance has beenmade for this in the cost estimate. The details of the run-off retention and pollutioncontrol arrangements would need to be agreed with the environment Agency and localdrainage authority.

2.7 Safety fencing and Street Lighting

2.7.1 New safety fencing would be provided on the A19 in front of the bridge abutments andon the side road embankment approaches to the bridge. The safety fencing is designedin accordance with the Highways Agency's Interim requirement for Road RestraintSystems (IRRRS) (Ref 3).

2.7.2 There is street lighting on the A19 but not on the side roads. Lighting columns on theA19 may need to be relocated on Option 1 but not on Option 2. However, dependingon the method of bridge construction, it may be necessary to temporarily remove someor all of the columns near the bridge.

2.8 Non-Motorised Users

2.8.1 Pedestrians, cyclists and equestrians are not specifically catered for in that there are nopaths or tracks for these users. It is assumed that because of the low numbers of theseusers, according to the traffic surveys and the traffic flows are also relatively light, thesenon-motorised users would walk or ride along the carriageway or verge. Option 1 wouldcater for cyclists in respect of gradient on the approaches to the bridge.

2.9 Utilities

2.9.1 Although the study did not include contact with utilities companies, the location of anumber of services was established during the site visit on 5 January 2005. With bothoptions, telecom cables and water mains may need to be sleeved and/or protected andan electricity pole may need resiting with Option 1.

2.10 Other Options

2.10.1 There is an existing junction scheme on the A1 trunk road at Rainton, which provides asimilar compact grade-separation to that proposed at the Black Swan Junction. Thestudy team visited the Rainton junction to gather ideas that might be included in thescheme put forward in the study. The main difference between Rainton and BlackSwan Options is that Rainton has a single lane bridge with traffic signal control. Duringthe site visit the traffic signals were observed to cause little delay to traffic using thebridge, although at the time of the visit traffic flow was very light. It was considered thatat the Black Swan junction it would be preferable in operational and maintenance termsto provide a two-way road throughout and avoid the use of signals. However, a singlelane bridge design and cost has been produced and the COBA network arranged tofacilitate the inclusion of signals if required. This was done to allow for the possibilitythat neither Option 1 nor Option 2 proved to be economic in COBA terms and a fall backposition of an option with a single lane bridge and signals could be tested.

3 Bridge Design and General Arrangement

Feasibility Study

3 Bridge Design and General Arrangement

3.1 Introduction

3.1.1 Alternative forms of construction are discussed that consider both a single and tow-lanecarriageway with accommodation for pedestrians. A summary comparison table of theoptions is included at the end of this section of the report.

3.1.2 The disruption effects of construction are considered and an estimated price for thecapital works for the structures only are provided. This review is based upon a desktopstudy with limited design work to merely verify the feasibility of the structural optionsthat are discussed in this report. No specific survey work or geotechnical investigationhas been carried out.

3.2 Description of Site and Geometric Constraints

3.2.1 The existing at grade junction is not signalled and originally provided bothnorthbound/southbound access from Trenholme Lane onto the A19 andeastbound/westbound access from the A19 onto Trenholme Lane. The central reservegap is currently closed by an experimental order that expires in January 2006.

3.2.2 The existing terrain is reasonably flat. To construct the compact grade separatedjunction, new earth embankments would be required to provide approaches to the siteof the proposed structure. Of the two highway alignment options, Option 1 is a distanceof 103 metres north of the junction and Option 2 is a distance of 86 metres north.Within these two options the provision of both a single and two-lane carriageway bridgefor the road crossing has been considered. With the highway face of the proposedabutments set back at 3.5 metres from the edge of the A19 carriageway a minimumtotal structure span of approximately 40 metres is required.

3.2.3 Although minimum headroom of 5.7 metres above the A19 would be desirable,minimum headroom of 5.3 metres, as permitted by the Highways Agency's DesignManual for Roads and Bridges (DMRB), has been assumed for this study. This hasbeen chosen in order to improve the vertical alignment and to reduce the extent of theapproach embankment works that are required. This has the consequence that theproposed bridge deck will be required to accommodate vehicle collision loads inaccordance with current standards. This may have the effect of increasing thesuperstructure costs; dependant upon the chosen structural form but this will be morethan offset by the cost savings associated with the reduced approach works. Thechosen highway vertical alignments result in an allowable superstructure constructiondepth, not including surfacing of 1.35 metres.

3.2.4 The proposed replacement of the existing junction removes the requirement of thesouthbound right turning lane off the A19 and therefore allows the option to widen thecentral reserve. As a result a central bridge support could be provided and this is alsoconsidered as an option.

3.3 Aspects Considered within the Design

3.3.1 Design and construction needs to take into account the following:-

• Provide solutions that minimise disruption to the traffic flow on the A19 during construction.
• Construction periods.
• Collision loads impacting on super and substructures.
• Aesthetics.
• Construction cost.
• Be easily maintainable.
• Buildability
• Heath and Safety
• Environmental aspects

The above are not stated in any order of priority.

3.3 Forms of Construction Considered

3.3.1 Superstructure

• Steel/Concrete Composite Deck.
• Pre-cast Pre-stressed Concrete Deck.
• Insitu Reinforced Concrete Deck.

3.3.2 Substructure

• Reinforced Concrete Bank Seat Abutments (Open Aspect).
• Reinforced Concrete Cantilever Abutments (Closed Aspect).
• Reinforced Concrete Cantilever Wingwalls.
• Reinforced Earth, Concrete Panel Clad, Wing Walls.

3.3.3 Foundations

• At this stage, we are unable to consider the most appropriate form of foundations with the absence of geotechnical information.

3.4 Discussion of Structural Forms

3.4.1 Superstructure

a. Insitu Reinforced Concrete Deck

With a central support providing a 2 span continuous structure, with equal spans ofapproximately 20 metres each, this type of deck is structurally viable option. Theminimum construction depth could be in the region of 1.1 metres with a reasonably highreinforcement percentage. With this construction depth the vertical highway alignmentcould be lowered resulting in cost savings with the approaches. Alternatively the fullallowable construction depth could be utilised resulting in a less heavily reinforced deck.

This type of deck could also be voided to significantly reduce the self-weight and hencethe reinforcement quantity and would also reduce loads on the substructure. Howeverit must be noted that contractors do not generally favour the provision of voids in areinforced concrete deck slab.

To construct the deck slab the required falsework and temporary works would result inlong closures of both carriageways of the A19.

Advantages

• Robust with regard to impact
• Alleviates the need for heavy lifting plant
• Lower construction costs than other options considered (this may be marginal)
• Lower maintenance costs than steel option.

Disadvantages

• Longer Construction period.
• Major disruption to traffic.
• High traffic management costs.
• Numerous concrete deliveries to site.
• Requires central support.

The above disadvantages make this an unfavourable option. Therefore this option hasnot been taken further.

b. Steel/Reinforced Concrete Composite Deck

This form of construction allows the provision of a single 40 metre span structure,resulting in an option with the lowest substructure costs. Due to the vertical alignmentconstraints the resulting span to depth ratio (30) lies at the very top of the acceptedrange. The construction depth will be equal to the desired maximum depth of 1.35metres. This will result in heavy lower flanges making this particular deck structure notas economical as this type of structure can be. However, the heavier lower flangeswould assist in resisting vehicular collision loads.

A two span structure of this type of construction could also be provided but is a lessfavourable option when compared to a similar structure of pre-cast pre-stressedconcrete. This option is therefore not considered further.

Refer to drawing numbers 31315/S/SK21 AND 31315/S/SK23 for general arrangementdetails of the single span option.

Advantages

• Least disruption to traffic than other options considered.
• Lower traffic management costs than other options considered.
• Aesthetically pleasing.
• Does not require central support.

Disadvantages

• Most susceptible to impact damage.
• Higher maintenance costs than other options considered.
• Requires heavy lifting plant but slightly less than the pre-cast concrete option.
• Total road closure required during beam lift.
• May require fabrication area adjacent to site.

c. Pre-cast Pre-stressed Concrete Deck.

A single 40 metre span structure is achievable with the largest of the SY type bridgebeams but the required construction depth would be approximately 2.2 metres, fargreater than the desired 1.35 metres. However, a two span option is viable using thesmaller Y type beams. This results in a construction depth of 1.15 metres thus allowingthe vertical alignment to be lowered producing possible cost savings with theapproaches.

Refer to drawing numbers 31315/S/SK20 and 31315/S/SK22 for general arrangementdetails of the two span option.

Advantages

• Reduced level of disruption to traffic when compared to the insitu r/c option.
• Lower maintenance costs than steel option.
• Does not require a total road closure.
• Robust with regard to impact.
• Shorter procurement period than steel.

Disadvantages

• Requires central support increasing disruption to traffic.
• Requires heavy lifting plant, slightly greater than the steel option.

3.4.2 Substructure

a. Reinforced Concrete Bank Seat Abutments (Open Aspect).

Considered on the basis of aesthetics, this method of superstructure support within thegeometrical constraints is only structurally viable for a two span structure. Two equalspans, of approximately 29 metres, could be provided in either steel/concrete compositeor pre-cast pre-stressed concrete construction. Bank seat abutments could bepositioned at the top of approximately 1 in 2 sloping revetments giving cost savings dueto the reduced approach works, when compared with a 'closed' abutment structure.Without pre-loading of the new earth embankment structures unacceptable settlementof the bank seats, designed as spread footings, are almost certain to occur. This willtherefore necessitate the use of piled foundations, that detract from any cost savingsthat the bank seats would have had when compared to vertical cantilever abutments.Another disadvantage is that due to the overall increase of the total deck span, the costof the superstructure would increase in the order of 50%, which would not make thisoption economically viable.

b. Reinforced Concrete Vertical Cantilever Abutments (Closed Aspect).

These comprise reinforced concrete retaining walls to the approach embankments thatgive end support to the deck structure. Positioned 3.5 metres from the edge of the A19carriageway they provide a 'closed' aspect, keeping the superstructure spans to aminimum. The faces of these could be clad in various materials with the aim ofaesthetically complimenting the local environment. However, a far less expensiveoption, which is generally acceptable is to provide a profiled patterned finish to thesurface of the concrete.

c. Reinforced Concrete Cantilever Wingwalls.

Using the same type of construction as the vertical cantilever abutments, thesestructures retain the sloping sides of the earth embankments. Finishes to these wallswould be as that applied to the abutment walls.

d. Reinforced Earth Concrete Panel Clad Wing Walls.

This form of construction is only deemed appropriate for the wing walls and not theabutment structures due to reinforced earth not being suitable to accommodatesignificant vertical loading. They are therefore considered as an alternative to thereinforced concrete option to be used in conjunction with reinforced concreteabutments. It seems generally accepted that they are more cost effective structureswhen compared to reinforced concrete retaining walls. However, considering theirrelatively short lengths, the unknown ground conditions and the absence of detaildesign it is difficult to judge at this stage what the most cost effective solution will be.

3.5 Traffic Management Considerations

3.5.1 The extent of traffic management during the construction period of this project will havea significant influence on the chosen structural option. The influence being in terms ofboth cost and disruption to the traffic on the A19.

3.5.2 During the abutment construction, due to the existing width of the carriageway, it maybe possible to accommodate two-lane running in both directions, assuming closure ofthe existing merge/diverge splays. With phased construction this may also be possibleduring the construction of a bridge support in the central reserve.

3.5.3 The construction of an in situ reinforced concrete deck will require closures to each ofthe northbound and southbound carriageways, in turn and for considerable period. Thismay be the overriding factor that forces the dismissal of this option.

3.5.4 During the 'lift in' of beams for the single span steel composite option then a total roadclosure of both carriageways will be required. This will probably be accommodated witha single overnight closure that would keep traffic management and disruption to aminimum.

3.5.5 The 'lift in' of pre-cast beams will require closures to each of the northbound andsouthbound carriageways in turn but for relatively short periods.

3.6 Costing Summary

3.6.1 A costing exercise has been carried out to determine the capital cost of the structurealone and has identified that there is only a small difference (just under 3%) for highwayOption 1 and Option 2. The costs in the table below are to be taken as representing thefirst quarter of 2005 and do not take into account the following:

• Temporary works.
• Approach works.
• Traffic management.
• Reinstatement works to the A19.
• Traffic signalling works associated with the single lane option.
• Preliminaries.
• Contingencies
• VAT.

Span	Deck Construction	Carriageway	Cost (£1000)
			Option 1	Option
1	Steel/Reinforced Concrete Composite	Two Lane	614	632
1	Steel/Reinforced Concrete Composite	Single Lane	416	428
2	Pre-Cast Pre-Stressed Concrete	Two Lane	640	658
2	Pre-Cast Pre-Stressed Concrete	Single Lane	443	456

3.7 Structural Options Summary

3.8.1 The structural options that have been considered have been summarised in thefollowing table. An attempt has been made to score each viable option by weightingeach of the design and construction considerations from 1 to 3, with 3 being of thehighest importance. Then each option has been given a rating with regards as to how itcompares with the other options within each category. Again using a scale of 1 to 3,where 3 mean it fares best.

Structural Options Summary Table (28KB PDF)

4 Environment and Land

Feasibility Study

4 Environment and Land

4.1

4.1.1 Preliminary assessments have been made of environmental effects (including noise, airquality, greenhouse gases, landscape, heritage, biodiversity, water environment,physical fitness and journey ambience), safety, economy, accessibility and integration.These are incorporated into the Project Assessment Report. No investigation has beenmade regarding the location of environmentally sensitive sites such as Sites of SpecialScientific Interest (SSSI) and archaeological remains.

4.1.2 Land affected by the scheme is assumed to be agricultural apart from a small area oftree planting alongside the A19 on the east side. The areas of land inside the loopshave been assumed to remain in private ownership and new access to them isprovided. It is possible that these areas may not be viable for agricultural use and mayattract additional compensation or purchase by the highway authority. Additional costsassociated with this are a risk that is covered by the Optimism Bias.

5 Scheme Costs

Feasibility Study

5 Scheme Costs

5.1

5.1.1 The rates used for calculating the scheme costs have been obtained from Spon's CivilEngineering and Highway Works Price Book and from analysis of Alvaston Bypasstender prices. The costs for various items of the works were also compared with theschedule of costs for the construction of the A1 Rainton Crossroads scheme providedby the Highways Agency.

5.1.2 The rates obtained from the various sources were adjusted using the December 2004ROADCON indices to bring all prices to the fourth quarter 2003 (4Q03). The 4Q03 isthe latest firm index quoted in ROADCON and has a value of 119. For land andcompensation costs, a rate was assessed based on experience on a recent ruralscheme. As no enquiries were made to the District Valuer, there is an element of riskwith the rate, which is covered by the Optimism Bias. For entry into COBA the value ofRPI used was 182.9 (4Q03).

5.1.3 No specific risk analysis was made of the cost information so the Adjustment Factor forOptimism Bias applied to the estimates is the value without risk assessment. From theShort PAR Guidance Version 3.2 Table C1, the scheme type is assessed as being astandard lesser highway scheme <£5 million requiring land acquisition and orders. Thestage of preparation is conception, giving an Optimism Bias value of 45%.

6 Traffic and Economics

Feasibility Study

6 Traffic and Economics

6.1 Background

6.1.1 The traffic and economics work was carried out in order to examine the economicfeasibility of providing a bridge at the Black Swan crossroads, with the existing gapclosure retained to provide 'left-in, left-out' movements at the former crossroadsjunction.

6.1.2 The Scheme was evaluated against two alternative 'Do-Minimum' scenarios:

• The original layout with the junction operating as an at-grade crossroads;
• The current interim layout with the gap closed and the junction providing left-in and left-out movements only.

6.1.3 Two alternative scheme options were examined. These are described at 2.5 above.The essential difference in terms of the traffic and economic assessments are thatOption 2 is more compact than Option 1 and therefore results in a slightly shorterdiversion route for right-turning traffic; and it is less costly to construct.

6.1.4 The traffic and economics work was based upon a spreadsheet model of link flows andturning movements likely to be affected by the Scheme and a COBA model of thejunction and the surrounding road network. A study area was selected aimed atincluding all the links and junctions likely to be affected by traffic displaced from theBlack Swan crossroads by the gap closure. The extent of the study area is shown onthe node-link network diagram contained at Appendix 1.

6.2 Traffic Data

6.2.1 The primary source of traffic flow data were the classified turning movement countsundertaken by Halcrow at the Black Swan and Ingleby Arncliffe junctions on Tuesday15th October 2002 (i.e. before the gap at the Black Swan was closed).

6.2.2 On the basis of these counts, Halcrow made an assessment of the diversion routeslikely to be used by traffic displaced from the Black Swan by the gap closure. Thesediversion routes are all included within the node-link network contained within the COBAmodel illustrated at Appendix 1.

6.2.3 Subsequently, data was made available from a before-and-after count undertaken byNorth Yorkshire County Council (NYCC) in March and November 2004. This new datasupported in general terms the diversion of traffic away from the local roads connectingwith the Black Swan junction but suggested that drivers had adopted slightly differentroutes than had been suggested in the Halcrow report. These routes, which wereadopted for the COBA assessment are described in the table below.

A19 Black Swan: Summary of Adopted Diversion Routes

Movement between	Direction	Predicted diverting flow	Route suggested by Halcrow	Route adopted for this study
The Rountons & Hutton Rudby	west to east	70	via Crathorne	50% via Crathorne; 50% via Ingleby Arncliffe
Hutton Rudby & The Rountons	east to west	48	via Crathorne	50% via Crathorne; 50% via Ingleby Arncliffe
The Rountons &	west to south	44	via East Harlesey	via East Harlesey
A19 Tontine (northbound) & Hutton Rudby	south to east	130	via A172 & C 27 Black Horse Lane (Swainby)	15% via A172 & Black Horse Lane (Swainby); 85% via A19 northbound & Crathorne
A19 Crathorne (southbound) & The Rountons, East Harlesey etc	north to west	70	via Crathorne Interchange, C152 (Long Lane) & C161 (York Street)	35% via C152 & C161; 65% via Ingleby Arncliffe crossroads (right turn) & East Harlesey

6.2.4 The traffic flows and re-assignments to the adopted diversion routes are outlined inAppendix 2.

6.2.5 Traffic flows were input into COBA as 12-hour weekday flows in October 2002, i.e. nofurther factoring was undertaken in order to convert the flows counted by Halcrow intoCOBA input flows. The underlying levels of use of minor roads away from the A19 wereestimated from the results of the NYCC counts.

6.2.6 A straightforward growth factor approach was taken to modelling the central 'ReferenceCase' and the high and low growth scenarios. At this stage, no competing orcomplementary schemes were considered, nor any planning applications nor local planled development allocations, as none were notified to us by the Project Sponsor.

6.2.7 The default traffic growth profile within COBA was used to represent the central'Reference Case' and high growth and low growth factors from the National RoadTraffic Forecasts (NRTF) for the high and low scenarios respectively. An approachbased upon default national growth rates was considered more appropriate than tryingto construct a localised growth profile based upon TEMPRO, at this stage in theScheme.

6.2.8 No allowance has been made for the effect of induced traffic, as there will be noperceptible saving in travel time for Trunk Road traffic. Any travel time saving for localusers is likely to be purely localised in its effect. Similarly, no allowance has been madefor the potential for land-use developments because none have been notified to thedesign team.

6.2.9 Accident data for the period January 1997 to May 2002 was made available. The wayin which accidents savings have been treated in this assessment is outlined under'Economic Assessment' below.

6.3 Economic Assessment

6.3.1 The method adopted was based on the use of COBA to evaluate on a common basissavings in accidents, journey time and fuel costs, and the cost of constructing theScheme. The version of COBA used was version 11, release 6 (COBA 11.6), releasedin August 2004, which embodies the current values of these items. It was determined inadvance that a QUADRO run would not be required, since queues and delays duringthe construction of the scheme are unlikely to be significant.

6.3.2 The following basic assumptions were embodied in the COBA runs:

• COBA was run for a 60 year assessment period in accordance with latest 'Green Book' guidance;
• The scheme was assumed to open in 2007, with the construction costs incurred in 2006-7 and preparation costs in 2005-6.
• The default values of discounting rate were used, i.e. 3.5% until 2033, thereafter 3.0%.
• The network was classified as 'Trunk Non-built-up' (TNB);
• The default values of seasonality index, E- and M-factor applicable to a TNB classification were used;
• National default growth factors for the Central, Low and High growth scenarios were used;
• National default vehicle category proportions were used (although classified counts were available, it was decided that because the majority of the traffic on the COBA network was A19 through traffic, the national defaults would provide a more robust approach).

6.3.3 Each of these assumptions could be reviewed and the default values replaced by locallyderived data as the scheme progresses if it is considered that further precision isrequired.

6.3.4 The extent of the COBA network was defined by the need to encompass all thediversion routes identified. A network diagram is included at Appendix 1. The junctionsat the Black Swan itself were modelled in COBA, together with the Ingleby Arncliffestaggered crossroads. Other junctions on the network were not modelled as such.

6.3.5 Link lengths and minor junctions per km were measured digitally from the O.S.mapping. Carriageway widths were measured on site. Values of other data items, suchas hilliness, bendiness, verge width etc were based upon default values in COBAadjusted to reflect local conditions where appropriate.

6.3.6 Local accident data was made available for the period January 1997 to May 2002. Itwas determined in advance that local accident data would be confined to the BlackSwan crossroads itself, since this was the primary location at which accident benefitswould be likely to be significant.

6.3.7 Having examined the history of the site, it was found that a local safety scheme wasimplemented at the Black Swan crossroads in September 2002 in advance of theclosure of the gap itself in July 2004. It was predicted by Halcrow in December 2002that improvements in the accident record were likely to result from the local safetyscheme. It would have to be accepted therefore, that even if the Black Swan gap wereto be re-opened with no further enhancements, the accident rate would not necessarilyrevert to that which applied before September 2002. Therefore, this earlier data couldnot be used. It is acknowledged that shortly after the safety scheme was put in placethere was a fatal accident at the junction. However, the time period between theimplementation of the safety scheme and the gap closure is too short to provide anaccident rate for input to COBA.`

6.3.8 The use of the accident data for the period after the local safety scheme but with thegap still open was also considered. Unfortunately, a period of 21 months is notnormally regarded as sufficient to allow local accident data to be used in COBA as it isnot regarded as statistically significant. It was intended to sensitivity-test the impact ofthis accident data on the COBA results, however, at the time of writing this report, theadditional data had not been received and this therefore proved not to be possible.

6.3.9 Scheme and land costs were input into COBA as 4th quarter 2003 estimates, asprepared by the design team. In addition, a further cost was input in the year 2047 torepresent a major reconstruction of the carriageway to acknowledge that a 60-yearassessment period demands an allowance for more than the routine maintenance andresurfacing that it is implicit in COBA. The bridge itself was assumed to have a designlife of 120 years and no further bridgework costs were assumed.

6.3.10 Validation of the COBA results was undertaken. In addition to checking the accuracy ofthe input data, the results were scrutinised to determine that link speeds, junctiondelays, overcapacity reports and the size and location of link, junction and accidentbenefits were within intuitively sensible ranges.

6.3.11 A detailed record of the results of the COBA runs are contained in Appendix 3 andbriefly summarised below.

A19 Black Swan COBA Results: Option 1 (Standard Scheme)
COBA Run	1	2	3	4	5	6
Growth Scenario	Reference Case		Low Growth		High Growth
Do Minimum	Gap Closed	Gap Open	Gap Closed	Gap Open	Gap Closed	Gap Open
Present Value of Benefits (PVB)	£4.471M	£3.156M	£3.998M	£2.523M	£4.900M	£3.727M
Present Value of Costs (PVC)	£3.520M	£2.910M	£3.475M	£2.910M	£3.560M	£2.910M
Net Present Value: (NPV)	£0.951M	£0.246M	£0.523M	-£0.387M	£1.340M	£0.817M
Benefit-to-cost ratio (BCR)	1.270	1.085	1.151	0.867	1.376	1.281
Accident Saving FYRR (number)	12.4 2.07%	77.4 2.20%	10.6 2.10%	66 2.20%	14.2 2.05%	88 2.20%

A19 Black Swan COBA Results: Option 2 (More Compact Scheme)
COBA Run	7	8	9	10	11	12
Growth Scenario	Reference Case		Low Growth		High Growth
Do Minimum	Gap Closed	Gap Open	Gap Closed	Gap Open	Gap Closed	Gap Open
Present Value of Benefits (PVB)	£4.601M	£3.291M	£4.118M	£2.651M	£5.309M	£3.874M
Present Value of Costs (PVC)	£3.191M	£2.582M	£3.146M	£2.580M	£3.232M	£2.582M
Net Present Value: (NPV) Benefit-to-cost ratio (BCR)	£1.410M 1.442	£0.709M 1.275	£0.972M 1.309	£0.071M 1.028	£1.807M 1.559	£1.292M 1.500
Accident Saving (number)	12.5	77.4	10.6	66.1	14.2	88
FYRR	2.29%	2.48%	2.32%	2.48%	2.26%	2.48%

Notes:

Costs and benefits are expressed in £ Million at 2002 market prices, discounted to 2002 within COBA.
Accident savings are total number of accidents saved over the 60-year assessment period.
FYRR = benefits arising in the first year of operation, expressed as a % of the scheme cost.

7 Project Appraisal Report

Feasibility Study

7 Project Appraisal Report

7.1 The Application of 'Project Appraisal Report' to the Scheme

7.1.1 The Project Appraisal Report (PAR) aims to summarise the environmental andeconomic impact of smaller Trunk Road schemes on a common basis.

7.1.2 In the case of the A19 Black Swan Bridge feasibility Study, it was determined that thereporting requirements at this stage of the project would be fulfilled by the use of aShort PAR. Accordingly, Short PAR Version 3.3 was used.

7.1.3 Two PARs have been completed for this study, representing layout Options 1 & 2,defined in Section 2.5 above. The PARs are contained in Appendix 4.

7.1.4 In line with advice from the client, the PARs reflect the evaluation of the Schemeagainst the existing, 'Gap Closed' Do Minimum case. For this reason, the Scheme isreported as being 'neutral' in terms of its accident assessment but 'beneficial' in termsof journey times because of the shorter routes that will become available to drivers oncethe bridge opens.

7.1.5 The structure of the short PAR is designed to report the safety and economy benefits ofa simple single-location scheme in which COBA has not been run and therefore theaccident and journey time benefits are calculated 'from first principles' by reference topredicted accident and delay reductions. There is no scope for reporting vehicleoperating cost benefits.

7.1.6 In the case of the A19 Black Swan Bridge Feasibility Study, it was decided at an earlystage to make use of COBA to evaluate the safety and economy benefits of theScheme. For this reason, although many of the elements of the PAR have been input,the safety and economy benefits are derived from the COBA results. Therefore noattempt has been made to calculate, for example, total time saved in opening yearbased upon peak hour flows and time savings.

7.1.7 The bridge proposed at the Black Swan comprises the final element of a package ofimprovement measures that commenced with a local safety scheme in September 2002and continued with the closure of the gap in July 2004. For this reason, the economicevaluation of the road safety benefits shows a very low first year rate of return. This isbecause the potential benefits associated with accident reductions at this specificlocation have largely already been realised.

7.1.8 In order to give a fuller picture of the road safety benefits of the whole package ofimprovement measures of the scheme, the 'road safety benefits' section of the PARcontains details of the accident record that occurred in the five years before both thegap closure and the local safety scheme that preceded it. However, the monetisedbenefits of the Scheme reported in the PAR are based on the COBA output accidentbenefits, which reflect the fact that the majority of these accident reductions havealready been achieved.

8 Conclusions and Recommendations

Feasibility Study

8 Conclusions and Recommendations

8.1 Conclusions

8.1.1 It has been possible to identify two Options to provide a compact grade-separatedjunction at the A19 Black Swan Crossroads.

8.1.2 Both of these would provide a loop road to the north of the existing junction, connectingthe two side road arms by means of a bridge over the A19. A number of forms of bridgeconstruction were considered and evaluated, albeit without the benefit of anygeotechnical investigation. The most favourable form of superstructure is considered tobe using single span steel/reinforced concrete composite. The relative merits of thesub-structure options could only be determined following a geotechnical investigation.

8.1.3 The essential difference between the two Options is that Option 1 complies with thedesirable minimum layout standards contained in TD 40/94 whereas Option 2 makesuse of some permitted relaxations to secure a more compact layout. Option 2, withbridge approach gradients greater then 5% would be less user friendly for cyclists.

8.1.4 In either case, the existing left-in, left-out junctions of the side roads with the A19 wouldbe retained, since these elements of the junction actually exceed the requirements ofTD40/94.

8.1.5 The economic assessment was undertaken using COBA and compares each of theOptions identified with two alternative Do Minimum cases, one with the gap remainingclosed in the Do-Min, the other with the gap re-opened. These assessments werecarried out for each of the low, central and high traffic growth profiles, ensuring that wehad examined a range of possible future scenarios wide enough to encompass anycredible future outcomes.

8.1.6 The results of the economic assessments show, with just one exception (Option 1assessed against the 'gap open do minimum' in the low traffic growth scenario), apositive economic result, indicating that the Scheme represents good value-for-money.As expected Option 2 out-performs Option 1 on account of its lower construction costsand more compact layout resulting in lower journey time penalties.

8.2 Recommendations

8.2.1 Subject to there not being a significant suppressed demand for cyclist use of a bridge,Option 2 is recommended for taking forward as an economic solution to providing agrade separated junction