A Notional Lane is part of the carriageway assumed solely for the purpose of applying specified live loads for the design or assessment of highway bridges. It does not normally have any relation to the physical lane markings painted on the carriageway.
The Carriageway Width is the width of running surface between kerbs, raised paving, barriers, etc. Where the running surface is divided by a physical obstruction (eg, a dual carriageway with central reserve) two separate carriageway widths are considered.
For assessment, marked lanes may be used if their width is less than 3.65m. Otherwise, values should be taken from the table:
| Carriageway Width | Notional Lanes | Lane Width |
|---|---|---|
| Less than 5.00m | 1 | 2.5m |
| 5.00m up to and including 7.50m | 2 | Width/2 |
| above 7.50m up to and including 10.95m | 3 | Width/3 |
| above 10.95m up to and including 14.60m | 4 | Width/4 |
| above 14.60m up to and including 18.25m | 5 | Width/5 |
| above 18.25m up to and including 21.90m | 6 | Width/6 |
| Carriageway Width | Notional Lanes | Lane Width |
|---|---|---|
| Less than 5.4m | 1 | 3.0m |
| 5.4m up to 6.0m exclusive | 2 | Width/2 |
| 6.0m inclusive to 9.0m exclusive | 2 | 3.0m |
| 9.0m inclusive to 12.0m exclusive | 3 | 3.0m |
| 12.0m inclusive to 15.0m exclusive | 4 | 3.0m |
| 15.0m inclusive to 18.0m exclusive | 5 | 3.0m |
| 18.0m inclusive to 21.0m exclusive | 6 | 3.0m |
Where lane widths do not add up to the carriageway width, the excess is designated the “remaining area” and given its own loading.