Explanation:

Importance of Illumination on Roads Carrying Fast Traffic:
Illumination plays a crucial role in ensuring safety on roads, especially on important roads carrying fast traffic. Adequate illumination is necessary to provide visibility and enhance the overall safety of drivers and pedestrians. Insufficient lighting can lead to accidents, decreased reaction time, and impaired visibility, which can be hazardous on roads with high-speed traffic.

Definition of Illumination:
Illumination refers to the amount of light falling on a surface or the intensity of light in a specific area. It is measured in lux, which is the International System of Units (SI) unit of illuminance.

Recommended Average Level of Illumination:
According to IRC (Indian Road Congress) recommendations, the average level of illumination on important roads carrying fast traffic should be 10 lux. This means that the surface of the road should receive 10 lux of light intensity to ensure adequate visibility.

Reasons for Recommending 10 Lux:
1. Safety: An average illumination level of 10 lux provides sufficient visibility for drivers to perceive road conditions, obstacles, and other vehicles in a timely manner. This helps in preventing accidents and ensuring the safety of both drivers and pedestrians.

2. Speed of Traffic: Roads carrying fast traffic require higher illumination levels compared to slower roads. Due to the higher speeds involved, drivers need more time to react to unexpected situations. With an average illumination level of 10 lux, drivers have a better chance of perceiving hazards and taking appropriate actions.

3. Uniformity: The recommended level of 10 lux ensures a uniform distribution of light across the road, minimizing areas of low visibility and shadowed spots. Uniform illumination helps in providing a clear view of the road ahead, reducing the risk of accidents due to sudden changes in lighting conditions.

4. Cost-Effectiveness: While higher illumination levels may enhance visibility further, they also require increased energy consumption and maintenance costs. The recommended level of 10 lux strikes a balance between visibility and cost-effectiveness, making it an optimal choice for roads carrying fast traffic.

5. Compliance with Standards: IRC recommendations are based on extensive research, analysis, and expert opinions in the field of road engineering. Adhering to these recommendations ensures compliance with established standards, promoting safer road infrastructure.

In conclusion, the recommended average level of illumination on important roads carrying fast traffic is 10 lux, providing adequate visibility, promoting safety, and balancing cost-effectiveness.

As per IRC - recommendation, the average level of illumination on important roads carrying fast traffic is 10 lux.