Highways Agency

A428 Caxton Common to Hardwick Improvement

7.0 Design Standards

General

7.1 Standards for the design of the road and its associated features are contained in the Department for Transport's "Design Manual for Roads and Bridges" (DMRB). Standards and Advice Notes referred to in the following paragraphs are:

• Volume 2 Highway Structures: Design (Substructures and Special Structures), Materials.
  • IAN 44/02 Interim Requirements for Road Restraint Systems (Vehicle and Pedestrian) (Deposit Document No. 46)
• Volume 5 Assessment and Preparation of Road Schemes
  • TA 46/97 Traffic Flows Ranges for use in the Assessment of New Rural Road Standards (Deposit Document No 40)
• Volume 6 Road Geometry
  • TD 9/93 Highway Link Design (Deposit Document No 34)
  • TD 16/93 Geometric Design of Roundabouts (Deposit Document No 35)
  • TA 23/81 Junctions and Accesses: Determination of Size of Roundabouts and Major/Minor Junctions (Deposit Document No 36)
  • TD 27/96 Cross sections and Headrooms (Deposit Document No 38)
  • TA 69/96 The Location and Layout of Lay-Bys (Deposit Document No 42)

7.2 The Scheme has been designed in accordance with these standards. The Scheme design has been undertaken to a level of detail that would enable the Orders to be made, as indicated in the 1:2500 scale engineering drawings (Deposit Document No. 22). The next stage of the design would be to develop it to the level of detailed design such that documents, including drawings, can be prepared to enable construction to take place. Detailed design would be carried out to suit the construction programme.

Scheme Standards

7.3 The carriageway width provision has been determined from TA 46/97 and TD9/93. Traffic flows on the proposed improved A428 are forecast at around 27,500 vehicles per day east of Cambourne and 31,000 vehicles per day west of Hardwick by the opening year of 2006. For this flow, a Dual two lane, all Purpose carriageway standard (D2AP) was selected. In accordance with TD 27/96, it would consist of dual 7.3m wide carriageways, with 1m wide hardstrips within 3.5m wide verges. The central reserve would generally be 4.5m wide including 1.0m wide hardstrips.

7.4 The design of the horizontal and vertical alignment of the proposed route is in accordance with TD9/93. The design speed for the main line of the Scheme is 120kph. This is approximately 70mph, the national speed limit for rural dual carriageways.

Caxton Gibbet Roundabout

7.5 At the western end of the Scheme, the proposed dual carriageway would tie directly into the existing Caxton Gibbet roundabout and only minor alterations to the roundabout would be necessary.

Bourn Overbridge

7.6 The Bourn side road would pass over the proposed dual carriageway. This side road has been designed for a side road design speed of 70kph.

Childerley Overbridge

7.7 The existing A428 would pass over the proposed dual carriageway at Childerley. This has been designed for a design speed of 85kph.

Hardwick Junction

7.8 At the eastern end of the Scheme near Hardwick a fully grade separated junction with two roundabouts (a 'dumbbell' layout) would be provided. The form of this junction complies with the recommendations contained in TA 48/92 and TD 22/92.

Drainage

7.9 To collect run-off from the road and to ensure stability of new cuttings and embankments, drainage measures would be incorporated. These measures would include for surface water control, reduction in pore water pressures and control of seepage from the slope face where appropriate. The drainage of the road surfaces would discharge into a piped system which would drain to balancing ponds. Surface water run-off would be controlled by the provision of drains at the top of the cutting slopes and at the bottom of embankments, to intercept surface water run-off from both the side slopes and natural topography. The surface water runoff from the embankments would be collected and directed into the boundary drainage.

7.10 The Scheme would, in accordance with Environment Agency requirements, incorporate measures to reduce potential contamination from silt, oil and accidental spillages. At drainage discharge points, where run off water enters watercourses, balancing ponds would be provided so that water can be discharged into watercourses in a controlled manner.

7.11 The ponds would control the discharge of the flows to green field runoff rates, maintaining the current flow levels within the existing watercourses. They would provide a method for containing runoff from the road at times of heavy rainfall. Any surge effect of the discharge would be reduced, which would avoid creating new flooding problems downstream.

Lighting

7.12 In accordance with design standards, it is not proposed to install lighting other than at the Hardwick junction and an extension to the existing lighting at Caxton Gibbet roundabout. (The existing Cambourne junction is lit.) Lighting would use full cut-off lanterns to reduce light pollution.

Safety Fencing

7.13 Safety fencing would be provided in the central reserve of the proposed dual carriageway. Additional safety fencing would be provided in the verge and on side roads adjacent to bridge piers, large traffic signs and other hazards.

Signing

7.14 Roadside signing would be of the reflectorised type generally mounted in the verge.

Highway Boundary Fencing

7.15 The Scheme would provide an all purpose trunk road for which there is no duty laid upon the Secretary of State for Transport to provide permanent boundary fencing. However, fencing would be provided where it is required due to badger activity. Any permanent boundary fencing that is erected would be carried out as accommodation works in lieu of compensation for the adjoining owner, after negotiation with the District Valuer. It is the practice of the Highways Agency to require the contractor to fence the site of the works as one of the first actions to be taken on commencing the construction contract. Where no permanent fencing is required, the contractor would be required to provide temporary fencing throughout the period of the contract.

Agricultural Accesses

7.16 In order to maintain the high standard of dual carriageway established for the Scheme, agricultural accesses would not be provided either onto or off the dual carriageway. In addition, no openings in the central reserve are included in the proposals for agricultural access, emergency access or any other use.

7.17 The Highways Agency has considered the future needs of agriculture and commerce and a number of access routes would be diverted by the provision of new tracks.

7.18 The inclusion of access in the draft Orders does not imply any particular form of construction. This would be a matter for compensation negotiations at a later stage.

Lay-bys

7.19 Lay-bys would be provided along the proposed carriageway in accordance with design standards.

Cyclists

7.20 All cyclists would be able to use the proposed dual carriageway although no special provision would be made for them. However, it is anticipated that cyclists will make more use of the existing road which will remain intact between Cambourne and Hardwick for local traffic use. A cycleway is proposed between the A1198 and the Elsworth Road so that cyclists can travel between Caxton Gibbet and Hardwick, without accessing the dual carriageway.