- Road categories 0 to 4 are based on the number of millions of standard axles (msa) carried by the road over a 20-year period. Reinstatements are designed on this basis.
Some roads that have been constructed in recent years (particularly new housing estate roads constructed under Section 38 of the Highways Act 1980) may have been designed and constructed to DMRB standards. In these cases, the authority must notify the undertaker, in advance of the works, and the undertaker must reinstate the excavation to match the existing construction thickness. It is not possible to match the engineering integrity of existing well-consolidated unbound layers with unbound reinstatement materials. Therefore, there may be significant differences between the existing carriageway construction and the requirements of the Code. The increased thickness of reinstatement materials compensates for this.
- For any road, its msa rating gives the number of standard axle loads that it is expected to carry over a defined period of time. This msa rating is calculated using the following input data:
- 24-hour annual average daily flow (AADF) of commercial vehicles in one direction. The use of AADF data in one direction, averaged from data in each direction, is recommended.
- Average vehicle axle factor over a 20-year service life.
- Actual sustained annual growth rate of commercial vehicles, averaged over several years, from valid census data.
Table NG1.1 – Maximum commercial vehicle traffic per road type Year of traffic count Daily traffic flow - Commercial vehicles/day one direction - Single or dual carriageway Average growth rate % Type 4 Type 3 Type 2 Type 1 Type 0 0 66 240 638 1383 4499 0 5 66 240 638 1383 4499 10 66 240 638 1383 4499 15 66 240 638 1383 4499 20 66 240 638 1383 4499 0 60 217 578 1253 4079 1 5 62 226 601 1304 4245 10 65 237 632 1370 4461 15 68 249 664 1440 4689 20 72 262 698 1514 4928 0 54 196 521 1132 3690 2 5 58 212 564 1225 3994 10 64 234 623 1353 4410 15 71 259 687 1494 4869 20 78 286 759 1649 5376 0 49 176 469 1020 3333 3 5 55 198 528 1148 3751 10 64 230 612 1331 4349 15 74 266 709 1543 5041 20 86 309 822 1789 5844 0 43 157 420 916 3005 4 5 50 184 491 1072 3515 10 61 223 598 1304 4277 15 74 272 727 1586 5204 20 91 331 885 1930 6331 0 39 140 375 821 2704 5 5 47 170 456 998 3287 10 61 317 582 1274 4195 15 77 277 742 1626 5354 20 99 354 948 2075 6833 0 35 125 334 734 2430 6 5 44 158 422 927 3068 10 59 211 564 1240 4105 15 79 283 755 1660 5494 20 106 378 1011 2221 7352 0 31 111 297 655 2180 7 5 41 145 389 859 2858 10 57 204 546 1204 4008 15 80 286 766 1689 5621 20 112 401 1074 2369 7884 0 27 98 263 584 1953 8 5 37 133 358 795 2657 10 54 196 526 1167 3904 15 79 288 772 1715 5736 20 117 423 1135 2520 8429 Note: The datum for year 0 is the time of the reinstatement - Where the actual AADF rates for any road are significantly different for each direction and Table NG1.1 indicates different road types in each direction, the highest traffic category applies in both directions.
- Where one-way traffic systems or other traffic management schemes result in multi-lane traffic, standard growth rate predictions and lane correction procedures may result in an inaccurate road classification overall. In such cases, whenever reasonably practical the flow of commercial vehicles should be monitored separately with traffic calculations completed for each traffic lane.
- Where an existing road is near or beyond its service life and is expected to be re-constructed within the foreseeable future, a temporary re-classification of the road will usually be appropriate pending re-construction. Such temporary re-classifications should be undertaken by agreement between the parties involved. Similarly, where roads are expected to be re-constructed within the guarantee period of the reinstatement, it will usually be appropriate to amend methods, materials or performance requirements for those reinstatements by agreement.
- The national network of roads carrying up to 125 msa within a 20-year period and classified as Types 0 to 4 roads according to the requirements of this Code will yield a distribution similar to that shown in Table NG1.2.
Table NG1.2 Estimated highway classification Road Type % of total 0 < 1 1 < 1 2 < 5 3 < 9 4 > 84 - It is expected that roads in any authority area will show a distribution similar to that shown in Table NG1.2, although there will be some local variations. In future years, there may be cases where traffic flows change to such a degree that re-classification will be necessary.
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