--- title: "Traffic control devices; traffic signal advantages" subject: "Transportation Engineering II" chapter: 1 key: "semester_7/transportation_engineering_ii:traffic-control-devices-signal-pros-cons" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/traffic-control-devices-signal-pros-cons site: BCT Engineering --- # Traffic control devices; traffic signal advantages Transportation Engineering II · Chapter 1: Traffic Engineering - Asked in: 2072 Chaitra, 8 marks - Video: [Traffic Control Devices | Transportation Engineering](https://www.youtube.com/watch?v=dJMW4ZATLpc) — APSEd - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/traffic-control-devices-signal-pros-cons - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-1 ## Question Describe various types of traffic control devices. Write down the advantages and disadvantages of traffic signal. ## Short answer Traffic control devices include signs, markings, signals, islands, speed humps, delineators, and barriers. Signal advantages: orderly movement, fewer right-angle crashes, safe pedestrian crossing, progressive flow; disadvantages: rear-end crashes, extra delay at low volumes, and installation/maintenance costs. ## Answer #### Types of traffic control devices 1. **Traffic signs:** regulatory, warning and informatory. 2. **Road markings:** pavement markings (centre line, edge line, lane lines, stop line, zebra crossing, arrows, hatching), kerb markings and object markers (IRC:35). 3. **Traffic signals:** fixed-time, vehicle-actuated and area-wide (coordinated) control, pedestrian signals, flashing beacons. 4. **Other devices:** traffic islands, speed breakers/humps (IRC:99), delineators, guard rails, barricades and variable message signs. #### Traffic signs (IRC:67) | Type | Purpose | Shape and colour | |---|---|---| | Regulatory (mandatory) | Tell the driver what to do or not do (stop, give way, no entry, speed limit, no parking) | Circular, red border, white background; STOP is an octagon, GIVE WAY an inverted triangle | | Cautionary (warning) | Warn of a hazard ahead (curve, steep descent, junction, school, narrow bridge) | Equilateral triangle, red border, white background, black symbol | | Informatory (guide) | Give directions, place names, distances, facilities (hospital, parking, fuel) | Rectangular; blue (facilities) or green (direction on highways) background, white letters | Subdivisions: informatory signs include direction signs, place identification signs, route markers, facility information and parking signs. **Placement:** within the cone of clear vision, about 2-3 m laterally from the carriageway edge, with a mounting height of 2.0-2.5 m above the ground; legends should be large enough to read at the speed of the road. #### Road markings (IRC:35) 1. **Carriageway (pavement) markings** - *Centre line:* separates the two directions (broken white or yellow, continuous at no-overtaking zones). - *Lane lines:* broken white lines that separate lanes in the same direction. - *Edge lines:* continuous white lines marking the carriageway edge. - *No-overtaking (barrier) lines:* continuous (single or double) yellow/white lines at sharp curves and crests. - *Stop line and give-way line:* at signals and intersections. - *Pedestrian crossings:* zebra (black and white bars). - *Arrows, words and symbols:* direction arrows, "STOP", "SLOW", "SCHOOL". - *Hatching and chevrons:* painted islands, approaches to obstructions. 2. **Kerb markings:** black/yellow or white bands on kerbs to show no parking or no stopping. 3. **Object markers:** painted black-white or yellow-black bands on poles, abutments and piers. 4. **Parking markings:** bay outlines. Markings must be visible at night (thermoplastic paint with glass beads), durable, skid resistant and uniform. #### Types of traffic signals - **Fixed-time (pre-timed):** fixed cycle and splits; cheap, suited to steady flows. - **Vehicle-actuated:** detectors change the green time according to demand. - **Coordinated/area control:** linked signals give a green wave (progressive flow). - **Pedestrian signals** and **flashing beacons.** **Advantages of traffic signals** - Give orderly movement of traffic and reduce right-angle (crossing) crashes. - Increase the capacity of an intersection that is not suitable for a rotary. - Allow pedestrians to cross safely. - Can be coordinated to give continuous (progressive) flow on arterial roads. - Give right of way to heavy flows, and the timings can be changed as volumes change. **Disadvantages** - Rear-end crashes may increase, and delay (stop-start) rises at low volumes. - Initial and maintenance costs, with dependence on power or batteries. - Failure of power or equipment can cause total chaos. - Red-light violations, driver impatience and extra fuel use. - Poor timing causes large delays and queues. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is NOT one of the main groups of traffic control devices? A. Traffic signs B. Road markings C. Traffic signals D. Vehicle engine controls Answer: D. Control devices are signs, markings, signals and other devices such as islands and humps. (Key point: Types of control devices) 2. Which sign description is correct? A. Warning signs are circular with a blue background B. Regulatory signs are circular with a red border; warning signs are triangular with a red border C. Informatory signs are triangular with red border D. STOP signs are inverted triangles Answer: B. Regulatory signs are circular (STOP is an octagon); warning signs are triangular; informatory signs are rectangular. (Key point: Sign classes and shapes) 3. Which is an advantage of traffic signals? A. They remove all delay B. They never need power C. They increase fuel use D. They reduce right-angle crashes and can be coordinated for progressive flow Answer: D. Signals give orderly movement, cut crossing crashes and allow green-wave coordination. (Key point: Advantages of signals) 4. Which is a disadvantage of traffic signals? A. Rear-end crashes and delay may increase, and power failure can cause chaos B. They reduce capacity at all intersections C. They cannot help pedestrians D. They cannot be timed to volume Answer: A. Signals have cost and power dependence, stop-start rear-end crashes, and poor timing causes queues. 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