--- title: "Driver vision characteristics affecting traffic" subject: "Transportation Engineering II" chapter: 1 key: "semester_7/transportation_engineering_ii:driver-vision-characteristics" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/driver-vision-characteristics site: BCT Engineering --- # Driver vision characteristics affecting traffic Transportation Engineering II · Chapter 1: Traffic Engineering - Asked in: 2081 Bhadra, 8 marks - Video: [HUMAN FACTORS IN TRAFFIC](https://www.youtube.com/watch?v=bK3wYAMl4hg) — Digital Driving School - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/driver-vision-characteristics - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-1 ## Question Discuss critical characteristics of driver related to vision that affect traffic performance. ## Short answer Key vision factors: visual acuity, cone of vision, peripheral vision, colour vision, glare recovery, depth perception, night adaptation. They set sign size/placement, signal positions, lighting, sight distances, and markings. ## Answer Vision supplies about 90 percent of the information a driver uses, so its characteristics control how a road must be designed. - **Visual acuity:** the ability to see detail. Static acuity is needed to read signs; dynamic acuity (seeing moving objects) is poorer and falls as speed rises. Sign letter height is chosen so that a driver of normal acuity can read the sign in the time available. - **Cone of vision:** clear vision is within about 3-5 degrees; fairly clear vision within about 10-12 degrees; useful peripheral vision up to about 120 degrees (about 160-180 degrees for detecting movement). Signs must be placed within the clear cone. - **Peripheral vision:** detects vehicles and pedestrians at the sides; it narrows with speed (from about 100 degrees at 40 km/h to about 40 degrees at 100 km/h) and with age and alcohol. - **Colour vision:** red, green and amber must be recognised. About 8 percent of males are colour blind, so signals also use fixed positions (red on top) and signs use standard shapes. - **Glare vision and recovery:** headlight glare at night reduces vision for several seconds. Recovery takes about 3 s when going from dark to light and about 6 s from light to dark, longer in old age. Hence anti-glare screens, median planting and properly aimed (dipped) headlights are used. - **Depth perception:** judging distance and relative speed is vital in overtaking and gap acceptance; it is poor at night and in fog. - **Night vision and adaptation:** the eye takes time to adapt to changes in light level, so lighting at tunnel entrances and underpasses must provide a gradual transition. The design consequences are: sign size and placement, retro-reflective markings, lighting levels, sight-distance lengths, and signal lens colours and positions. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. About what share of driving information comes through vision? A. About 10 percent B. About 40 percent C. About 60 percent D. About 90 percent Answer: D. Vision supplies about 90 percent of the information a driver uses. (Key point: Importance of vision) 2. How does peripheral vision change with speed? A. It widens as speed rises B. It is unaffected C. It narrows, from about 100 degrees at 30 km/h to about 40 degrees at 100 km/h D. It disappears at 50 km/h Answer: C. Higher speed narrows the field of view, so side hazards are detected less. (Key point: Peripheral vision and speed) 3. What design measures address glare recovery time of about 3-6 s? A. Wider lanes B. Anti-glare screens, median planting and low-mounted headlights C. Lower signs D. Brighter signals Answer: B. These measures reduce headlight glare, since vision is reduced for several seconds after glare. (Key point: Glare recovery) 4. Why do signals use fixed positions (red on top) as well as colour? A. About 8 percent of males are colour blind B. To save power C. Because amber is hard to see D. To reduce cost Answer: A. Colour blindness is common among males, so position and shape also convey the message. 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