--- title: "Accident causes and prevention; street light design" subject: "Transportation Engineering II" chapter: 1 key: "semester_7/transportation_engineering_ii:accident-causes-prevention-street-light-factors" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/accident-causes-prevention-street-light-factors site: BCT Engineering --- # Accident causes and prevention; street light design Transportation Engineering II · Chapter 1: Traffic Engineering - Asked in: 2075 Chaitra, 8 marks - Video: [introduction of traffic engineer ,accident ,causes of accident, junction and types of junction](https://www.youtube.com/watch?v=-JgDOYRfm5Y) — conceptual academy - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/accident-causes-prevention-street-light-factors - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-1 ## Question What are the causes of accident and how accident can be prevented? Describe briefly the factors influencing street light design. ## Short answer Accidents stem from human error (speeding, intoxication), vehicle defects, poor road geometry, and environmental factors. Prevention follows the 5 E's: engineering, education, enforcement, encouragement, emergency services. Street lighting design considers road type, mounting height (8-10 m), spacing (3-5× height), lamp type, arrangement, overhang, uniformity ratio (~0.3-0.4), and glare control. ## Answer #### Causes of accidents 1. **Road user (human) factors:** over-speeding, drunk or drowsy driving, overtaking in unsafe places, ignoring signals, jaywalking, lack of experience or training, fatigue, using mobile phones. These account for about 80-90 percent of crashes. 2. **Vehicle factors:** brake failure, tyre burst, steering defects, overloading, defective lights, poor maintenance and lack of fitness tests. 3. **Road and geometric factors:** sharp curves, poor sight distance, narrow carriageways and bridges, insufficient superelevation, slippery or damaged pavement, absence of shoulders, poor intersection design. 4. **Traffic control factors:** missing or confusing signs, signals and markings, absent or poor lighting. 5. **Environmental factors:** rain, fog, snow, landslides and flooding (especially important in Nepal's hilly roads); night-time. 6. **Other causes:** animals on the road, poor enforcement of law and lack of emergency services. **Preventive measures — the 5 E's** - **Engineering:** safe geometric design, adequate sight distance, proper superelevation, signs, markings, guard rails, crash barriers, street lighting, speed humps, pedestrian crossings and bridges, black-spot treatment, road safety audit. - **Education:** driver training and licensing, school programmes, public awareness campaigns and media. - **Enforcement:** speed and drunk-driving checks, helmet and seat-belt laws, vehicle fitness inspection, penalty and demerit points under the Motor Vehicles and Transport Management Act 2049. - **Encouragement:** reward safe drivers; promote safety culture and use of protective equipment. - **Emergency services:** quick ambulance and first aid, trauma care and a good crash reporting system (IRC:53 forms A-1 and A-4). #### Factors influencing 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 factor accounts for about 80-90 percent of crashes? A. Vehicle defects B. Road user (human) factors C. Weather D. Animals Answer: B. Human factors such as over-speeding and drunk driving cause most crashes. (Key point: Main cause) 2. Which set matches the 5 E's of prevention? A. Engineering, Education, Enforcement, Encouragement, Emergency services B. Economy, Education, Engine, Enforcement, Emission C. Engineering, Energy, Education, Evaluation, Emergency D. Education, Employment, Enforcement, Engines, Environment Answer: A. The 5 E's are Engineering, Education, Enforcement, Encouragement and Emergency services. (Key point: Five E's) 3. Street light spacing is typically what multiple of mounting height? A. 0.5 to 1 times B. 3 to 5 times C. 10 to 15 times D. Equal to road width always Answer: B. Spacing is typically 3 to 5 times the mounting height; the ratio controls uniformity. (Key point: Spacing) 4. What is the uniformity ratio in street lighting? A. Maximum to minimum illuminance, about 10 B. Minimum to average illuminance, about 0.3 to 0.4 C. Lamp wattage to pole height D. Spacing to road width Answer: B. Uniformity ratio is minimum-to-average illuminance, about 0.3 to 0.4. 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