Appendix C 1.2 Traffic Data
Traffic – 6000 AADT, including 18% heavy vehicles, consisting of:
- standard heavy vehicles = 10% (SHV)
- large heavy vehicles = 8% (LHV).
Assume traffic is equal over the two carriageways, thus each carriageway carries 6000/2 = 3000 vehicles per day.
Determine the volume of each vehicle type in each carriageway:
- Volume of light vehicles = 82% of 3000 = 2460
- Volume of standard heavy vehicles = 10% of 3000 = 300
- Volume of large heavy vehicles = 8% of 3000 = 240.
An assumption on the proportion of traffic in each lane must be made (Section 5.2.4). It is assumed that the traffic is distributed in the proportions listed in Table C 1.
Table C 1: Distribution of traffic
| Vehicle Type | Outside Lane (LH) | Median lane (RH) |
|---|---|---|
| Light vehicles | 60% | 40% |
| SHV | 80% | 20% |
| LHV | 100% | 0% |
It is reasonable to assume that almost all of the SHV, and 100% of the LHV will travel in the outside lane.
The volume of each vehicle type, and the resultant percentage of equivalent heavy vehicles (Equation 2), must be calculated for each lane to make an appropriate adjustment to the basic voids factor.
The volumes of vehicles in each lane is calculated as per Table C 2.
Table C 2: Vehicle volume by lane
| Vehicle Type | Outside Lane (LH) | Median lane (RH) |
|---|---|---|
| Light vehicles | 60% of 2460 = 1476 | 40% of 2460 = 984 |
| SHV | 80% of 300 = 240 | 20% of 300 = 60 |
| LHV | 100% of 240 = 240 | 0% of 240 = 0 |
| Total (v/l/d) | 1956 | 1044 |
Therefore, using Equation 2 (Section 5.2.5), EHV(%) can be calculated:
Outside lane EHV (%) = SHV(%) + (LHV(%) x 3)
= (240/1956 x 100) + ((240/1956 x 3) x 100)
= 12.3 + 36.8 = 49.1% = Adopt 49%
Median lane EHV (%) = SHV(%) + (LHV(%) x 3)
= (60/1044 x 100) + 0
= 5.7% = Adopt 6%
An EHV(%) of 10% will be assumed for the shoulder.
Due to the uphill grade, traffic volume and high proportion of heavy vehicles in the outside line, a HSS1 seal has been selected for the reseal.