2.0 Engineering requirements

Engineering requirements for adopted highway have traditionally followed standards set out in the DfT Design Manual for Road and Bridgeworks (DMRB). These requirements primarily remain in place, however, in recognition that these design standards may be onerous for residential streets the DfT produced Manual for Streets 1 in 2007 to assist in the design process for sustainable and safe neighbourhoods.

2.1 Manual for streets

Manual for Streets introduced a significant change and new approach to street design from that set out in DMRB CD109 Highway link design. MfS initially focused on 'lightly trafficked residential streets with an important public realm function beyond the movement of traffic' It is not intended to be adopted for high-capacity distributor roads where DMRB standards still apply. The council welcomes the approach adopted in MfS and MfS2 and are keen to engage with all practitioners to build areas with distinct public realm and a sense of place and purpose.

Where roads are entirely residential in nature and do not carry through-traffic, the principles outlined in Manual for Streets should be applied. This may have the effect of reducing the need for excessive splays, forward visibility and radii, in favour of promoting lower speeds and more responsible driver behaviour.

MfS and MfS2 can have contradictory interpretation by practitioners charged with the development of streets and space. For this reason, it is considered important to define what we consider are acceptable and pertinent points from the guidance.

Setting out our view of highways development will assist developers, their consultants and designers in bringing forward acceptable streets suitable for adoption.

A street is difficult to define and can be considered to be anything from a short residential highway with access to a low number of properties, to a major retail 'High Street' with a mix of residential, retail and commercial businesses. MfS principles can apply to all highways in built up areas. However, we would request all practitioners to pay particular cognisance to the place and movement requirements of a street and to consider the differences between a street and its sense of place and a road whose primary function is to carry traffic. The hierarchy of movement with pedestrians placed ahead of all other users is an appropriate starting point for sense of place. Highways with little cross carriageway pedestrian movement and carrying flows of traffic in excess of 300vph are not considered suitable for MfS application. However, it must be emphasised that all situations are different, and it is essentia

l that transport planning officers within the council's Built and Natural Environment Team are consulted as soon as possible to scope the 'Place' and 'movement' aspects of any proposal. We consider MfS should apply where public realm and pedestrian movement are at the heart of the street, where traffic volumes are not a significant concern and where vehicle speeds are not cause for concern.

A very important aspect of MfS and one which will potentially bring forward previously unsuitable sites is the aspect of safe stopping distances. DMRB safe stopping distances (SSD) have been used previous to MfS. However, evidence supporting MfS indicates SSD can be relaxed.

Subject to all other aspects of proposals being acceptable the council will support development where design speeds are below 30mph or where evidence from speed surveys can be used to calculate SSD below DMRB standards.

The council will ordinarily expect standards set down in DMRB to apply in instances where highways carry traffic with speeds in excess of 40mph. The difference in highways where application of MfS principles and those where more stringent design standards are applied can and will be blurred. Therefore, it is essential that early discussions are held with Council officers and a design code is established if necessary. Council officers acting on behalf of the Local Highway Authority will always consider movement of pedestrians and vulnerable road users as a significant factor on whether MfS applies. Highways with little public realm activity, where properties are set back from the highway with little direct highway frontage and where applicable low levels of public transport will not be considered suitable. Community function with streets as spaces for integration not segregation will be an important consideration.

2.2 Pavement construction standards

For all proposed adopted highway works where pavements are in bituminous materials, the pavement design of the bituminous layers must be carried out in accordance with DMRB: Pavement CD 226 Design for new pavement construction (formerly HD 26/06).

All bituminous surfacing must have a declaration of performance and be CE marked. All delivery tickets must also be CE marked. This applies to Asphalt Concrete BS EN13108-1 and Hot Rolled Asphalt BS EN 13108-4.

All bituminous surfacing must be laid by contractors with current UKAS National Highways Sector Scheme for Quality Management in Highway Works 16 for the laying of asphalt mixes.

All material shall be compacted in accordance with the Specification for Highway Works.

The subbase must be protected from contamination and tracking of mud once laid to base level. Any contaminated surface must be removed and dressed to finished subbase level prior to application of base/binder courses.

Recycled subbases must be produced in accordance with clause 803 and tested in accordance with clause 710. The supplier's WRAP quality protocol and relevant testing must be provided to GC one week prior to any material arriving on site. Material must be stockpiled prior to use within the permanent works to allow testing to be completed prior to laying. All material laid prior to the outcome of test results is subject to rejection.

2.2.1 Pavement foundation design

Pavement Foundation Design is in accordance with CD 225 - Design for new pavement foundations.

The designs in section 2.1.4 have been based upon a minimum stiffness modulus of the subgrade of 35MPa (3% CBR). Subgrades with a design subgrade surface modulus value lower than 35 MPa (3% CBR) are unsuitable to support the construction of a pavement foundation without further improvement.

If the stiffness modulus of the subgrade is less than 35MPa (3% CBR) then the subbase should be increased by a depth of 100mm. If the subgrade is found to be less than 35MPa(3% CBR) then the subgrade must be improved in accordance CD225

Note: In areas where insitu CBR readings are less than 2% then ground improvement will apply in accordance with CD225. Overdig soft spots by 300mm increments and replace with capping material.

The developer must confirm the CBR/ stiffness modulus to GC via testing carried out by an independent UKAS accredited laboratory which holds current accreditation for the required test.

The number and location of tests is to be agreed with the appointed representative of GC based on site conditions.

Sub-formation drainage must be provided to allow egress of any water which has entered the pavement foundation and to prevent water rising to within 600mm of formation level.

2.2.2 Road construction

The tables below set out the acceptable construction for the indication classification of roads. If more than 20 Million Standard Axles (msa) then a suitable design in accordance with DMRB needs to be submitted to GC.

General

• All material to be in accordance with SHW series 900 unless specified in this document.
• All cold edges, including previously laid asphalt, against which hot bituminous mixtures are to be laid to form joints shall be treated with hot bituminous binder with a penetration of not less than 40 pen. All other products are specifically excluded.
• Recycled material is not permitted in the surface and binder course.

Surface course

Aggregate abrasion Value (AAV) to be in accordance with HD 36/06 Table 3.2.

Polished stone Value (PSV) of Pre-coated chippings (PCC) to be in accordance with HD 36/03

Table 3.1

Texture depth (TD) to SHW clause 921 Table 9/3

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