NG2 Performance Requirements
NG2.1 There are no Notes for Guidance
NG2.2 Surface Profile
NG2.2.1 There are no Notes for Guidance
NG2.2.2 Edge Depression - Intervention
Freedom from excessive edge depressions, or 'trips', for all pedestrians and two wheeled vehicles, is considered to be one of the most important performance requirements. Given that pedestrians and various two wheeled vehicles are likely to use or cross any roads, footways and cycle tracks, it is considered necessary to set a single limit for all edge depressions.
NG2.2.3 Surface Depression - Intervention
Excessive surface depressions will reduce ride quality and give rise to noise and vibration. The maximum depth of surface depression within the area of a reinstatement is limited to approximately 2.5% of the width of reinstatement, which represents a mean slope of 1 in 20 (5% gradient). In order to prevent excessive areas of standing water, it is considered necessary to limit the maximum depth of a surface depression to 25 mm, regardless of the reinstatement width.
NG2.2.4 Surface Crowning - Intervention
Excessive surface crowning will reduce ride quality and give rise to noise and vibration. The maximum height of crowning within the area of a reinstatement is limited to approximately 2.5% of the width of the reinstatement, which represents a mean slope of 1 in 20 (5% gradient). In order to prevent excessive surface irregularity, it is considered necessary to limit the maximum height of crowning to 25 mm, regardless of the reinstatement width.
NG2.2.5 Combined Defect - Intervention
The intervention limits specified for surface depressions and surface crowning include a reduction in the intervention limit, to 80% of the tabulated value, subject to a minimum of 10 mm, where surface depressions and/or crowning and/or edge depressions abut. The individual features shall be measured, and the reduction applied, as follows:
1) Combination Depressions
Where an edge depression abuts an area of surface depression, then the area of abutting depression should be measured as shown in Figure NG2.2. Any surface crowning also abutting the area of combined depressions should be measured separately, as shown in Figure NG2.3. The permitted depth of a combination depression is further limited if the depression results in standing water.
2) Combination Crowning
Where an area of surface crowning abuts an edge depression, or a surface depression, or any combination thereof, then the area of abutting crowning should be measured as shown in Figure NG2.3. The area of abutting depression should be measured separately, as shown in Figure NG2.2. The maximum height of combination crowning is further limited if the crowning results in standing water.
NG2.2.6 There are no Notes for Guidance
NG2.3 Fixed Features
Fixed features, e.g. kerbstones and related precast concrete products, channel blocks and drainage fixtures, surface boxes and ironware, should be bedded on a sound foundation, in accordance with the owner's requirements. In order to prevent excessive areas of standing water, it is considered necessary to set separate intervention limits for channel blocks, drainage fixtures, surface boxes and ironware.
NG2.4 Surface Regularity
Where the use of a rolling straightedge is not permitted, the surface regularity shall be assessed on an agreed basis.
NG2.5 Structural Integrity
1) Reinstatement materials and compaction requirements have been specified in order to safeguard the pavement structure, both within and adjacent to the reinstatement. Any substantial or rapid settlement within a reinstatement may therefore indicate a potential reduction in the stability of the adjacent pavement structure, as well as potential defects within the reinstatement.
2) There will be cases, in adverse circumstances, where the correct application of this Specification, in all respects, will still result in levels of settlement within the reinstatement that do not meet the requirements of Section S2.5, Structural Integrity. For example, the type and condition of the adjacent ground and/or pavement structure may limit the degree of compaction that can be achieved, so influencing the amount of settlement that could occur.
3) Any engineering investigation is intended only to determine the likelihood and extent of any further settlement, and the most cost-effective and convenient method of restoring the structural stability and surface performance of failed sections of a reinstatement, to a satisfactory condition.
4) In the case of large or deep excavations, it may be appropriate for an Authority and an Undertaker to agree an extended interim guarantee period, with additional interim surfacing materials laid to restore the running surface. When no further consolidation or settlement is considered likely, a permanent binder course and surface course may be laid, and the permanent guarantee period initiated. In any event, the location and extent of any re-excavation should be mutually agreed, taking full advantage of any bound materials already in place.
NG2.6 Skid Resistance
1) An adequate skid resistance of the reinstated running surface must be maintained, by selection of the polished stone value (PSV), aggregate abrasion value (AAV) and texture depth of the aggregate exposed at the road surface. The exposed aggregate may be precoated chippings rolled into the surface (HRA), coarse aggregate within the surface course, coated material to BS 594987 or any chippings or other aggregate applied in any form of surface dressing or slurry sealing treatment.
2) Smaller reinstatements constitute a much lower degree of skidding risk, but the measurement of skid resistance, texture depth and surface regularity become progressively more difficult as the reinstatement width reduces. However, material requirements and laying conditions remain unchanged and it is expected that the skid resistance of smaller reinstatements will not be significantly different.
3) For the purposes of identifying reinstatement sites where the risk of skidding is potentially high (Site A), sections of carriageway of greater than 10% gradient should be identified from existing steep hill warning signs or by notification from the Authority. Similarly, bends of less than 100 metres radius in roads where the speed limit is greater than 40 mph (65 kph) should be identified from existing bend, double bend or chevron warning signs or by notification from the Authority.
4) Given good site conditions, it is possible to obtain reasonably representative measurements of skid resistance and surface regularity on narrower reinstatements but amended test procedures and/or extra care are required. The TRL Mini Texture Meter and TRL Rolling Straightedge should always be fully contained within the limits of the reinstatement. The actual minimum practicable width for these instruments will depend on the trench alignment and radius of curvature. Measurements can be particularly difficult when testing on tight radius bends.
5) The Undertaker should require the suppliers of bituminous materials to regularly supply details of the constituent materials within their bituminous mixtures and in particular PSV/AAV test results for the coarse aggregate in Surface Course mixtures and the aggregate used for precoated chippings in HRA.
6) The past use of Table S2.7 has indicated that the minimum values noted are appropriate in most cases.
NG2.7 There are no Notes for Guidance