The 1985 IRC 93 code presents detailed recommendations for the design and setup of road traffic signals across India. It covers aspects such as positioning of signal faces, lens dimensions, signal phasing, and operational standards to aid traffic engineers and planners in managing intersection control effectively, ensuring pedestrian safety and optimal signal visibility.
Overview
The 1985 IRC 93 code presents detailed recommendations for the design and setup of road traffic signals across India. It covers aspects such as positioning of signal faces, lens dimensions, signal phasing, and operational standards to aid traffic engineers and planners in managing intersection control effectively, ensuring pedestrian safety and optimal signal visibility.
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Frequently Asked
Per IRC 93, the minimum visibility distance for traffic signal faces depends on the 85th percentile or average vehicle approach speed. Signal faces should be continuously visible from distances specified in the standard, ranging from 45 meters at 35 km/h to 185 meters at 100 km/h. Each illuminated signal lens, except for pedestrian signals, should be visible from a minimum of 400 meters under normal conditions. This ensures sufficient reaction time and enhances intersection safety.
IRC 93 mandates that pedestrian signals be independently controlled with clear 'Walk' and 'Don't Walk' indications to safeguard pedestrians. The crossing time is calculated based on the crossing width and an average pedestrian speed of 1.2 m/s, allowing adequate time for safe passage. These signals should be synchronized with vehicular signals to avoid conflicting movements, and may include audible or tactile features for visually impaired users.
According to IRC 93 Clause 6.1, signal lenses must be circular, with standard net diameters of either 200 mm or 300 mm. The 300 mm lenses are preferred for better visibility at critical locations such as busy or high-speed roads, while 200 mm lenses are suitable for less demanding scenarios. Lenses are arranged vertically or horizontally depending on the signal face design, ensuring clear visibility and compliance with regulations.
Signal phasing and cycle duration under IRC 93 are calculated based on vehicle volumes and headway times: a reaction time of 6 seconds for the first vehicle and 2 seconds for each subsequent vehicle. The total cycle length includes all phases plus amber periods and is optimized using saturation flow rates and lost time estimates. Phases consist of green, amber, clearance amber, and red intervals, with coordination aimed at minimizing delays and ensuring safe pedestrian clearance.
IRC 93 specifies that the primary signal face should be positioned near the intersection on the left side of the approaching traffic, typically at the stop line. The secondary signal face is installed farther along the approach, approximately 12 to 36 meters beyond the stop line on the right side, often on the footpath or median island. This arrangement maximizes visibility and ensures clear communication of traffic control to drivers.
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