H.—4o,

The main point disclosed by this table is that over 75 per cent, of the bridges on the rural roads of this country are timber bridges with a probable average life of from twenty-five to thirty years. The Main Highways Board have compiled a very valuable bridge register for all bridges on main highways, and a summary of this register gives the following results : —

Table B.—Bridges over 25ft. in Length on Main Highways.

An investigation of the register in relation to the timber bridges gave the results set out hereunder :—

Table C. —Age of Timber Bridges on Main Highways.

The Main Highways Board have a definite programme for the replacement of defective and obsolete bridges, and it is therefore proposed to investigate the position of the bridges on rural roads other than main highways. The total length of timber bridges over 25 ft. in length on all rural roads, including main highways, is 377,767 ft., while the main highways account for 146,553 ft., leaving a balance of 231,214 ft. on rural roads other than main highways. In the absence of any reliable data concerning the age of timber bridges on rural roads other than main highways, it is assumed that the ages of these timber bridges would be comparable with those on the main highways, and on this assumption the following table shows the position :—

Table D.—Age of Timber Bridges on Rural Roads other than Main Highways.

This table indicates that 64 per cent., or 147,977 ft., of the timber bridges on the rural roads other than main highways were built over twenty years ago, while 36 per cent., or 83,237 ft., are over the age of thirty years. In view of the vital importance of bridges to land transport, it appears essential that a definite bridge-renewal programme similar to that being carried out by the Main Highways Board should be put in hand with the object of replacing within the next ten years 147,977 ft. of bridging on the rural roads other than main highways. To replace these timber bridges with concrete would cost approximately £15 per foot, and the total sum to be provided would be approximately £2,250,000. By adopting concrete for replacement, all materials, with the exception of reinforcing-steel, would be available within New Zealand.

15

Type of Construction. iLength, in Feet. XotaTLength Concrete or stone .. .. .. .. j 27,700 11-8 Concrete, steel, and timber combination .. .. 61,448 26-0 Timber, including New Zealand timber and Australian hardwood .. .. .. .. .. 146,553 62-2 Totals .. .. .. .. .. 235,701 100-0

Age of Bridges. j Length, in Feet. 6 Under 10 years .. .. .. .. 20,517 | 14 10 years to 20 years . . . . . . . . 32,242 22 20 years to 30 years . . .. . . . . 41,035 28 30 years to 40 years .. .. .. .. 33,707 23 40 years to 50 years .. .. .. .. 14,655 10 Over 50 years . . . . . . .. 4,397 3 Totals .. .. .. .. 146,553 i 100

Age of Bridges. ! length, in Percentage 5 6 I Feet. of Total. U-: ;| : .; Under 10 years .. .. . . . . .. 32,370 14 10 years to 20 years . . .. .. .. .. 50,867 22 20 years to 30 years . . .. .. .. .. 64,740 28 30 years to 40 years .. .. .. .. .. 53,179 23 40 years to 50 years . . .. .. .. .. 23,122 10 Over 50 years .. .. .. .. .. 6,936 3 Totals .. .. .. .. .. 231,214 100