--- title: "Traffic engineering; road user characteristics and HVE" subject: "Transportation Engineering II" chapter: 1 key: "semester_7/transportation_engineering_ii:te-definition-road-user-hve" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/te-definition-road-user-hve site: BCT Engineering --- # Traffic engineering; road user characteristics and HVE Transportation Engineering II · Chapter 1: Traffic Engineering - Asked in: 2073 Shrawan, 8 marks - Video: [Highway~Transportation Lec 10~U3~Traffic Engineering Part A Traffic Characteristics by BK Mahawar](https://www.youtube.com/watch?v=taWzGJXvZNU) — BHARAT KM Online पाठशाला - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/te-definition-road-user-hve - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-1 ## Question Define traffic engineering. Explain road user characteristics and human-vehicle-environment system. ## Short answer Traffic engineering plans, designs, and operates roads for safe, efficient movement. Road user characteristics include PIEV reaction time (2.5 s), pedestrian speed 1.2 m/s, and physical/mental traits. The human-vehicle-environment system integrates driver, vehicle, and road, with driver error as the main crash cause. ## Answer #### Definition of traffic engineering **Traffic engineering** is the branch of transportation engineering that deals with the planning, geometric design, operation and control of roads, their networks, terminals and adjacent land use, so that people and goods move safely, quickly, comfortably, economically and with least harm to the environment. (Institute of Transportation Engineers definition, as used in Khanna and Justo.) Its scope covers traffic characteristics, traffic studies (volume, speed, O-D, parking, accident), traffic regulation and control, geometric design, traffic signs, markings and signals, road lighting, and traffic planning and management, including the Nepal Motor Vehicles and Transport Management Act and the Department of Roads (DoR) rules for enforcement. #### 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, need separate lanes and safe turning at intersections. 6. **Age and gender, fatigue, intoxication and disability:** these add to 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 (in Nepal mixed traffic is common). 8. **Mixed traffic:** in Nepal slow and fast vehicles share the carriageway, so wider shoulders and segregation are required. #### Human-vehicle-environment system The traffic stream is the combined behaviour of three interacting elements: the **Human (road user)**, the **Vehicle** and the **Environment (road and surroundings)**. Safe and efficient flow needs all three to match. ```text +--------------+ | HUMAN | driver, pedestrian, | (perception, | cyclist, passenger | reaction) | +------+-------+ controls| ^ feedback v | +------+----+--+ +--------------------+ | VEHICLE |<---->| ENVIRONMENT | | size, power, | | road geometry, | | brakes, load | | surface, signs, | +--------------+ | weather, lighting | +--------------------+ ``` - **Human:** receives information (mostly visual), decides and acts (steering, braking). Errors in perception, judgement or reaction are the main cause of crashes (about 80-90 percent involve human error). - **Vehicle:** its dimensions, weight, power, braking and visibility set the road width, gradient, curve radius and pavement strength required. - **Environment:** road geometry, surface friction, traffic control devices, lighting, weather and adjacent land use affect how the driver sees and responds. A mismatch in any one (for example a fast vehicle, a sharp curve and a wet surface) causes crashes, so design must fit the "design driver" and "design vehicle" to the road. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Traffic engineering mainly deals with which of the following? A. Only the structural design of pavements B. Planning, geometric design, operation and control of roads and their traffic for safe, quick, economic movement C. Only enforcing traffic laws D. Only the design of vehicles Answer: B. It covers planning, design, operation and control of roads, networks, terminals and land use for safe and efficient movement. (Key point: Definition of traffic engineering) 2. What reaction time is used in sight distance design? A. About 0.25 s B. About 1.2 s C. About 10 s D. About 2.5 s Answer: D. The PIEV time of about 2.5 s is used for stopping, headlight and intersection sight distances. (Key point: PIEV reaction time) 3. Why does design use a conservative value such as the 15th-percentile pedestrian speed? A. To cover the slower, more vulnerable users because users vary in age, fatigue and ability B. Because most pedestrians walk at that speed C. To reduce the cost of crossings D. Because faster pedestrians never use crossings Answer: A. Variation among users means design must accommodate slower users so that crossing time is adequate. (Key point: Design basis for pedestrians) 4. What is the key idea of the human-vehicle-environment system? A. Only the vehicle decides safety B. Only road geometry matters C. The three elements are independent D. All three interact, and a mismatch in any one can cause crashes Answer: D. Safe flow needs human, vehicle and environment to match; for example a fast vehicle on a sharp wet curve causes a crash. (Key point: Human-vehicle-environment system) ## Related in Transportation Engineering II - [Human-vehicle-environment system; driver characteristics](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Ahve-system-driver-physical-characteristics) — Transportation Engineering II, chapter 1 - [Critical road user and static vehicle characteristics](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aroad-user-static-vehicle-characteristics) — Transportation Engineering II, chapter 1 - [Traffic engineering; road users and vehicular characteristics](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Ate-definition-road-users-vehicular) — Transportation Engineering II, chapter 1 - [Road user characteristics and their importance](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aroad-user-characteristics-importance) — Transportation Engineering II, chapter 1 ## Related in other subjects - [Human civilization, development and the environment](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Acivilization-development-environment-history) — Environment and Pollution Control, chapter 7 - [Hybrid vehicle and environment impact](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Ahybrid-vehicle) — Energy Environment and Society, chapter 5, asked 2×