HC Deb 18 May 1995 vol 260 cc346-8W
Mr. Gordon Prentice

To ask the Secretary of State for Transport what is the cost of(a) laying and (b) maintaining 100 yards of (i) porous and (ii) conventional asphalt. [23863]

Mr. Watts

This is an operational matter for the Highways Agency. I have asked the chief executive to write to the hon. Member.

Letter from Lawrie Haynes to Mr. Gordon Prentice, dated 18 May 1995: The Minister for Railways and Roads, Mr. John Watts MP, has asked me to write to you in reply to your recent Parliamentary Question concerning the cost of (a) laying and (b) maintaining 100 yards of (i) porous asphalt and (ii) conventional asphalt. My previous answer of 8 March quoted a range of prices for one kilometre length within a typical surfacing contract. Prices for a 100 yards length would be approximately 10% of those quoted figures. For instance a two lane dual carriageway all purpose road would be £10,000 to £20,000 for porous asphalt and £7,000 to £10,000 for conventional asphalt. I should point out that where only short lengths such as 100 yards are to be surfaced the costs would rise substantially for both porous asphalt and conventional asphalt due to the increased impact of fixed site costs. As we have little experience of such working we are unable to be more precise. Differences in maintenance cost between porous asphalt and conventional asphalt relate chiefly to the need for more frequent resurfacing with porous asphalt, the extra cost of the porous asphalt material and the more frequent salting operations needed for porous asphalt in winter. It is currently not possible to give any representative information on the additional cost of salting given the limited amount of porous asphalt which has been laid and the recent mild winters. However, I am able to give you an indication of the difference in material and laying costs. Broadly speaking, maintaining a porous asphalt surface over the life of a road will be of the order of double the cost of maintaining a conventional asphalt surface. This does not take into account the effect of traffic delays during roadworks which will add to the cost of maintaining porous asphalt because of the need for more frequent resurfacing. As explained in my letter the costs are influenced by numerous factors such as traffic and climatic conditions. These also have an influence on the life of a road surface. Consequently the performance of the different surfaces will vary significantly from site to site.

Mr. Chidgey

To ask the Secretary of State for Transport what are the locations of the sections of Britain's motorways that currently have porous asphalt surfacing; what total length of motorways is covered in porous asphalt surfacing; and what total length of motorway covered in porous asphalt surfacing currently have traffic levels (a) below and (b) above 75,000 vehicles per day. [24300]

Mr. Watts

This is an operational matter for the Highways Agency. I have asked the chief executive to write to the hon. Member.

Letter from Lawrie Haynes to Mr. David Chidgey, dated 18 May 1995: The Minister for Railways and Roads, Mr. John Watts MP, has asked me to write to you in reply to your recent Parliamentary Question concerning the locations of lengths of porous asphalt laid on motorways throughout Britain and of those the total lengths carrying above and below 75,000 vehicles per day. You will appreciate that the Secretary of State for Transport and the Highways Agency are responsible only for roads in England. Roads in Scotland and Wales are the responsibility of the appropriate Secretaries of State and I am not able to provide information to you for those areas. Porous asphalt surfacings have been used within two long term trials on the M1 in Yorkshire and on the M6 in Lancashire. In addition, porous surfaces have been used on the M40 (Junction 6 - Postcombe) and on the M25 widening (Junctions 7–8) currently under construction. To date the total length of motorway covered with porous asphalt is approximately 4.5 miles excluding the trials. These trials comprise approximately 1.1 miles but in each case it is only one or part of one of the two carriageways which has been treated. None of the lengths with porous asphalt surfacing carry flows less than 75,000 vehicles per day.

Mr. Chidgey

To ask the Secretary of State for Transport, pursuant to his answer of 9 May,Official Report, columns 351–52, in what specific circumstances porous asphalt is considered not to be technically suitable as a noise mitigation measure on motorways. [24461]

Mr. Watts

This is an operational matter for the Highways Agency. I have asked the chief executive to write to the hon. Member.

Letter from Lawrie Haynes to Mr. David Chidgey, dated 18 May 1995: The Minister for Railways and Roads, Mr. John Watts MP, has asked me to write to you in reply to your recent Parliamentary Question concerning the specific circumstances porous asphalt is considered not to be technically suitable as a noise mitigation measure on motorways. The technical limitations on the use of porous asphalt on motorways and other trunk roads are set out in the Design Manual for Roads and Bridges, Volume 7, Section 2, Part 4, HD27/94 as published by HMSO. This states that porous asphalt should not be used in the following situations:

  1. a) On areas where the pavement strength is sub-standard.
  2. b) On areas where there is considerable acceleration, braking, turning and parking.
  3. c) On tight radius curves, and loops of radii less than 75 metres, or when gradients exceed 10 per cent., without advice from the Overseeing Department.
  4. d) On areas where excessive deposits of detritus or oil and fuel may be experienced; such as parking areas, exits from farms and quarries and other industrial sites.
  5. e) On areas where the use of tracked vehicles, construction plant, farm equipment or similar industrial vehicles is expected.
  6. f) On areas where the cross-fall is insufficient to remove water to the road edge such that flooding may occur in the porous asphalt.
  7. g) At locations where free drainage cannot be accommodated along the low edge of the surfacing; for example abutting other types of construction such as a concrete carriageway.
  8. h) Generally on lengths of carriageway less than 100m, because of spray carry-over from adjacent surfacing, unless special conditions prevail.
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  9. i) Where cyclists use the carriageway and where kerbs are provided, unless provision is made to ensure drainage design overcomes any possible safety hazards.
  10. j) On existing new bridges where it is not possible to adequately drain the surface.
  11. k) In urban environments, where frequent excavations by statutory undertakers may occur.
  12. l) Where traffic levels exceed 4,000 commercial vehicles per lane per day, at opening, without reference to the Overseeing Department. This is being extended to embrace traffic levels up to 6,000.
Porous asphalt is not recommended for use on jointed concrete or flexible composite road pavements without seeking advice from the Overseeing Department. Additionally, it is not recommended for certain steel deck bridges. Whilst the above limitations currently apply the Highways Agency has implemented a research programme to see if it is possible to produce more durable porous asphalt and reduce the number of limitations.