--- title: "Street lighting importance and design factors" subject: "Transportation Engineering II" chapter: 1 key: "semester_7/transportation_engineering_ii:street-lighting-importance-design-factors" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/street-lighting-importance-design-factors site: BCT Engineering --- # Street lighting importance and design factors Transportation Engineering II · Chapter 1: Traffic Engineering - Asked in: 2072 Chaitra, 8 marks - Video: [DESIGN FACTORS FOR STREET LIGHTING](https://www.youtube.com/watch?v=z4qhP40vuH0) — Animesh Awasthi - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/street-lighting-importance-design-factors - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-1 ## Question What are the importance of street lighting? Describe the factors affecting street light design. ## Short answer Street lighting improves night visibility, reduces crashes and crime, and increases capacity and guidance. Design factors: road type and traffic, mounting height, spacing, lamp type and distribution, arrangement, lateral offset, uniformity ratio, glare control, maintenance factor, and cost. ## Answer #### Importance of street lighting - It **improves night visibility** so that drivers see the road, obstacles, pedestrians and other vehicles in time to stop. - It **reduces crashes** and the severity of crashes at intersections, curves, bridges, and pedestrian crossings. - It **improves personal security** and reduces crime in urban areas. - It **increases the capacity and speed** of the road after dark by raising the confidence of the driver. - It **helps traffic flow and the economic life** of commercial areas (night shopping, tourism). - It **gives guidance** to the driver on road alignment, junctions and the edge of the pavement, and it enhances the look of the city. #### Factors affecting street light design 1. **Type of road and traffic volume:** arterial, collector or local street decides the illumination level (lux) and uniformity (about 30 lux on important roads, 15 lux on secondary, 8 lux on residential roads in Indian practice). 2. **Mounting height (H):** usually 8-10 m on main roads, 6-7.5 m on minor roads; higher poles give more uniform light and reduce glare but need more power. 3. **Spacing (S):** typically 3 to 5 times the mounting height; the spacing-to-height ratio controls uniformity. 4. **Lamp type and luminous flux:** LED, high-pressure sodium or mercury; wattage and lumen output. 5. **Luminaire type, light distribution and tilt (cut-off, semi-cut-off, non-cut-off).** 6. **Arrangement of the lamps:** single side, staggered, opposite, central (median) or suspended. 7. **Lateral offset or overhang:** the position of the post from the carriageway edge (about 0.6 m minimum clear from the kerb; 1.5 m or more on high-speed roads). 8. **Uniformity ratio:** minimum-to-average illuminance, about 0.3 to 0.4. 9. **Glare control, maintenance factor (about 0.7-0.8), cost, local environment (trees, dust), and power availability.** ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is a main benefit of street lighting? A. It improves night visibility and reduces crashes B. It reduces daytime capacity C. It removes the need for signs D. It increases vehicle speed limits by law Answer: A. Lighting lets drivers see the road, obstacles and pedestrians in time, reducing night crashes. (Key point: Importance of street lighting) 2. What is the typical spacing of lamps in relation to mounting height H? A. Equal to H B. About 10 to 15 times H C. 3 to 5 times H D. Less than H/2 Answer: C. Spacing is typically 3 to 5 times the mounting height; the S/H ratio controls uniformity. (Key point: Spacing and mounting height) 3. What does a higher pole give? A. Less uniform light and more glare B. More uniform light and less glare, but more power needed C. Lower cost and more glare D. No change in uniformity Answer: B. Higher poles spread light more evenly and reduce glare but need more power. (Key point: Effect of mounting height) 4. What is the uniformity ratio? A. Maximum to minimum illuminance, about 3 to 4 B. Pole height to spacing C. Minimum to average illuminance, about 0.3 to 0.4 D. Lamp wattage to lumen output Answer: C. Uniformity is minimum divided by average illuminance, typically 0.3 to 0.4. 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