Accident causes and prevention; street light design

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.