Traffic control devices; traffic signal advantages

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)

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.