--- title: "Critical road user and static vehicle characteristics" subject: "Transportation Engineering II" chapter: 1 key: "semester_7/transportation_engineering_ii:road-user-static-vehicle-characteristics" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/road-user-static-vehicle-characteristics site: BCT Engineering --- # Critical road user and static vehicle characteristics Transportation Engineering II · Chapter 1: Traffic Engineering - Asked in: 2082 Bhadra, 4+4 marks - Video: [Highway Engineering Static Characteristics Most important Quick Revision Classes SSC-JE Sub-Engineer](https://www.youtube.com/watch?v=kRT_D8JwETw) — Civil Site Plus - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/road-user-static-vehicle-characteristics - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-1 ## Question Describe the critical road user characteristics to be considered in traffic engineering design. Discuss, how static characteristic of vehicle affect road design? ## Short answer Road user characteristics are physical vision/hearing/strength, mental attention/judgement/attitude, PIEV reaction time (2.5 s), pedestrian speed 1.2 m/s and cyclist behaviour. Vehicle static dimensions fix design: width sets lane width, height sets clearance, length and turning radius set parking and intersection radii, and axle load sets pavement thickness. ## Answer #### Critical road user characteristics 1. **Physical:** vision (acuity, field of vision, colour vision, glare), hearing, strength and agility. They fix sign sizes, letter heights, lighting, sight distances and footpath gradients. 2. **Mental and psychological:** attention, judgement, emotional stability and attitude. They influence overtaking decisions, gap acceptance and compliance with signals. 3. **Reaction time (PIEV):** about 2.5 s is used for stopping sight distance, headlight sight distance and intersection sight distance (IRC:SP:23, IRC:66, Nepal Road Standard 2070). 4. **Pedestrian characteristics:** walking speed about 1.2 m/s (IRC:103 and IRC:93 use 1.2 m/s; slower, about 0.9 m/s, for children and the elderly); space needed about 0.5-0.75 m² per person; they need footpaths, crossings, refuge islands and signal time. 5. **Cyclists:** speed 10-25 km/h; they need separate lanes and safe turning at intersections. 6. **Age and gender, fatigue, intoxication and disability:** these add to the variation, so design uses the 85th-percentile or a conservative value (for example the 15th-percentile pedestrian speed for crossing time). 7. **Behaviour and compliance:** lane discipline, helmet and seat-belt use, jaywalking and parking habits vary by country and must be reflected in the design and enforcement plan. 8. **Mixed traffic:** in Nepal slow and fast vehicles share the carriageway, so wider shoulders and segregation are required. #### How static characteristics of a vehicle affect road design | Characteristic | Typical value | Effect on road design | |---|---|---| | Width | 2.5 m (trucks, buses) | Lane width (3.5 m rural, 3.0-3.25 m urban), parking bay width | | Height | 3.8 m normal, up to 4.75 m (IRC) | Vertical clearance under bridges and underpasses (5.5 m minimum, IRC:54) | | Length | 11-12 m rigid, 16 m semi-trailer, 18 m truck-trailer | Parking bays, curve widening, kerb radius, passing and storage lanes | | Wheel base and overhang | 6-7 m (truck) | Extra widening on curves, minimum turning radius, tail swing | | Ground clearance | 0.2-0.3 m | Hump, drain and vertical-curve design | | Turning radius | 12-14 m (truck) | Minimum intersection radius, island and median-opening design | | Weight and axle load | 10.2 t legal single axle; 8.16 t standard axle in IRC:37 | Pavement thickness, bridge loading (IRC:6) | | Eye and object height | driver eye 1.2 m, object 0.15 m (IRC:SP:23) | Sight distance at crests | Examples: the 2.5 m width and 11 m length of a bus fix the minimum bay size; the 4.75 m height fixes bridge clearance; the large turning radius of trucks fixes the radius of intersection corners; the axle load fixes pavement thickness. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What perception-reaction time does the answer use for stopping, headlight and intersection sight distance? A. 0.5 s B. 1.0 s C. 1.5 s D. 2.5 s Answer: D. About 2.5 s is used for these sight distances (IRC:SP:23, IRC:66, Nepal Road Standard 2070). (Key point: Design reaction time) 2. Because road users vary by age, fatigue and disability, how does design handle them? A. Uses the fastest user's value B. Uses the 85th-percentile or a conservative value, such as the 15th-percentile pedestrian speed for crossing time C. Ignores the variation D. Uses the average of all users exactly Answer: B. Design uses percentile or conservative values, so slow pedestrians still get enough crossing time. (Key point: Conservative design for variation) 3. Which static vehicle characteristic fixes the vertical clearance under bridges and tunnels? A. Width B. Turning radius C. Height D. Axle load Answer: C. Vehicle height (up to 4.75 m) fixes the vertical clearance (5.5 m minimum). (Key point: Vehicle height effect) 4. Which pairing of vehicle characteristic and design element is correct? A. Axle load - pavement thickness; turning radius - intersection corner radius B. Axle load - lane width; turning radius - bridge clearance C. Ground clearance - lane width; width - pavement thickness D. Length - pavement thickness; height - kerb radius Answer: A. Axle load fixes pavement thickness and the large turning radius of trucks fixes intersection corner radius. 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