 |
 |
| Road Type |
Classification |
Terrain |
Maximum AADT for given LOS (12% HCV) |
| C |
D |
E |
Reduced
2 Lane
(2 x 3.5 + 0.5m) |
National
Secondary |
Level |
4,800 |
8,600 |
15,600 |
Standard
2 Lane
(2 x 3.75 + 3.0m) |
Rural
Commuter |
Level
Level |
6,500
8,400 |
11,600
15,000 |
20,600
26,800 |
Wide 2
lane
(2 x 5.0 + 2.5m) |
Rural
Commuter |
Level
Level |
7,700
10,000 |
13,800
17,900 |
24,600
32,000 |
Reduced
Dual C/way
(2 x 7.5 + 1.0m) |
Rural
Commuter |
Level
Level |
20,800
27,000 |
26,500
34,400 |
32,100
41,800 |
Dual
C/way
(2 x 7.5 + 3.0m) |
Rural
Commuter |
Level
Level |
34,600
45,000 |
44,100
57,400 |
53,500
69,600 |
Motorway
(2 x 7.5 + 3.0m) |
Rural
Commuter |
Level
Level |
43,500
56,500 |
55,500
72,000 |
62,500
81,200 |
| NRA |
National Roads Authority |
| AADT |
Average Annual Daily Traffic
(vehicles per day) |
| LOS |
Level of Service |
| LOS - C |
Average speed 84 kph (during the
thirty most congested hours per annum)* |
| LOS - D |
Average speed 80 kph (during the
thirty most congested hours per annum)* |
| LOS - E |
Average speed 72 kph (during the
thirty most congested hours per annum)* |
| HCV |
Heavy Commercial Vehicles |
|
|
*Note (not spelled out in NRA document):
The Annual Average Daily Traffic (AADT) figures given in this table are the numbers of vehicles which the roadway can support so that the desired level of service is exceeded for all but the thirty most congested hours of the year.
Two examples follow to demonstrate what I mean:
Example 1:
A rural standard two lane roadway can handle an average daily flow of 11,600 vehicles (at level of service D which is 80kph), and within this figure allowance is made for the busy periods (bank holidays etc.) when peaks occur, so that only on the thirty busiest peak hours in the year will the average speed fall to 80kph. In reality, on a day when 11,600 vehicles use the
road, the average speed will be higher than 80kph.
Example 2:
A daily average of 56,500 vehicles can use a commuter motorway, and this motorway will operate at better than level of service C (which is 105kph) for all except for the thirty busiest peak hours in the year, when average speeds will drop to (or below) an average of 105kph. On a day when 56,500 vehicles use the roadway the average speed will be above 105kph. Needless to say, on a day when less than 56,500 vehicles use the roadway the average speed will be even higher.
Level of service:
This concept is based on ensuring that the network can satisfy a demanded minimum standard of service to the road-user. The study recommends that this minimum objective of 80kph inter-urban speed be maintained on all 2-lane single carriageway roads. The inter-urban speed on divided roads would be higher. (Page 18)
Consideration was given to a wide range of road characteristics, in applying HCM (the USA highway capacity manual), including type of terrain, percentage passing zones, percentage heavy vehicles, passenger car equivalency for heavy vehicles, directional distribution of traffic, peak hour factors, development/access points factor, narrow lanes and restricted lateral clearance, use of hard-shoulders and wide lanes, in determining the capacities for inter-urban and commuter roads.
The road type must cater for peak traffic conditions. However, the highest hourly traffic flow in a year is considered an unreasonable standard which would involve gross under-utilisation of the road. Practice has been to adopt as a design standard the 30th highest hour traffic flow, that is the hourly traffic flow which would be expected to be exceeded for thirty hours in a year. (Page 31)
|
 |
