Applying the criteria from 5.4 above to an 11.5m residential collector road using 150W HPS (Cooper OVZ15SR22E Type II) luminaries on 35-8 poles, the results may be seen in Table 5.2.
Table
5.2: Cost Comparison – Residential Collector Road
|
Guideline |
Optimum Spacing |
Lights per 500m |
Increased Cost |
|
TAC |
36.2m |
14 |
55% |
|
IES |
62.18m |
9 |
|
Applying the above criteria on a 9.5m residential local road using 100W HPS (Cooper OVZ15SR22E Type II luminaries on 30-8 poles, as illustrated in Table 5.3.
Table
5.3: Cost Comparison – Residential Local Road
|
Guideline |
Optimum Spacing |
Lights per 500m |
Increased Cost |
|
TAC |
45.11m |
12 |
33% |
|
IES |
60.66m |
9 |
|
These examples illustrate that for typical subdivision type roads; there are significant cost savings to be gained in using IESNA over RTAC. Furthermore, the extended span lengths afforded make it easier to design a good lighting system utilizing the available locations in a subdivision for installing streetlights.
The above examples are based on a straight road. In a typical subdivision, with curves and cul-de-sacs, the savings would not be as great.