5.2 Design Traffic
The traffic volume and type have a major impact on the outcome of a seal design, and therefore appropriate and accurate traffic volumes are an essential requirement for the determination of the rates of application of binder.
For seal design, a best estimate of the traffic using each lane is required. A separate sprayed seal design is required for each lane of traffic having either a different traffic volume (v/l/d) and/or different proportion of heavy vehicles. The traffic determined for the lane to be sealed is termed the design traffic.
Design traffic, when determined from AADT, must take into account the following:
- the number of carriageways (generally single or dual)
- the direction of traffic (one-way or two-way)
- number of lanes
- percentage of the total traffic travelling in each lane
- the number of heavy vehicles travelling in each lane.
The design traffic includes all light and heavy vehicles that travel in that lane, as per Equation 1:
| Design traffic = Light vehicles + SHV + LHV | 1 | |||
| where | ||||
| Light vehicles | = | number of light vehicles in the traffic mix (i.e. Austroads vehicle Classes 1 and 2) | ||
| SHV | = | number of standard heavy vehicles in the traffic mix (i.e. Austroads vehicle Classes 3 to 9) | ||
| LHV | = | number of large heavy vehicles in the traffic mix (i.e. Austroads vehicle Classes 10 and above) |
For the purpose of this design method, where general references are made to typical traffic volumes, the following descriptions apply:
- very low: ≤ 200 v/l/d
- low: 201–750 v/l/d
- medium: 751–2000 v/l/d
- high: > 2000 v/l/d.