IRC 30:1968 is the Indian Standard (IRC) for standard letters and numerals of different heights for use on highway signs. IRC 30:1968 provides standard letter and numeral proportions, heights, and legibility criteria for Indian road signage — covering directional, informational, warning, and distance signs across all road types from urban streets to expressways. Letter heights scale with design speed: 100-140 mm for urban (30-50 kmph), 200-300 mm for highway (80-100 kmph), 300-400 mm for expressway (120 kmph). Critical for legibility from driving distance — letters too small are unreadable, too large waste sign area. Font style specifies 1:0.7-0.8 height:width ratio with 1/7 stroke width. Colour contrast minimum 70% (white on green, white on blue, black on yellow). Hindi/Devanagari and regional scripts integrated at same heights. Amendment No. 1 (2015) added LED-illuminated signs, variable message signs (VMS), and electronic speed limit signs. Amendment No. 2 (2022) updated for autonomous vehicle recognition — standardized symbol recognition, higher-contrast markings, emerging needs for machine-readable signs. IRC 30 is often referenced alongside IRC 35 (sign specifications) and IRC 67 (retro-reflective standards).
Specifies the proportions, letter/numeral heights, and layout standards for text on highway signs — legend, direction, route, distance, and informational signs — ensuring legibility from design distance.
- Status
- Current
- Usage level
- Specialized
- Domain
- Transportation — Traffic Engineering
- Type
- Standard
- Amendments
- Amendment No. 1 (2015) — LED-illuminated signs, Variable Message Signs (VMS), electronic speed limit signs; Amendment No. 2 (2022) — autonomous vehicle recognition, machine-readable signs
Also on InfraLens for IRC 30
Practical Notes
! Letter height selection: rule of thumb 25 mm per 10 kmph of design speed. For 80 kmph road: 200 mm letters. Below this, drivers can't read at speed.
! Regional language signs (Hindi + state + English) required on NH — 3-line format common. Use same letter heights across all languages to ensure legibility.
! Transport Medium font is standard — UK-derived, adapted for Devanagari. Used across Europe, India, Australia. Sans-serif, rounded terminals, highly legible.
! Multi-line signs: keep consistent letter height across lines; line spacing 1/2 letter height minimum. Overly-crowded signs become unreadable.
! Colour contrast: white on green (directional) is most common. Black on yellow (warning) highest visibility. Avoid low-contrast colours (dark green on black).
! Retroreflective sheeting: Type III (micro-prismatic) is now standard for highway signs. Type IV (super-prism) for expressways. Type II (engineering grade) OK for urban streets.
! Night legibility: retroreflective sheeting returns headlight beam to driver. Quality sheeting returns 300-500 candela per lux; cheap returns 50-100 cd/lx. Specify Type III minimum.
! Sign degradation: retroreflective sheeting degrades 10-30% per year in Indian climate (UV + monsoon humidity). Replace signs every 5-7 years to maintain legibility.
! LED-illuminated signs (Amendment No. 1, 2015): self-illuminated for nighttime reading without headlight dependence. Solar-battery powered. Cost ₹15-50k per sign vs ₹3-8k for retroreflective.
! Variable Message Signs (VMS): can display changing content (traffic information, detour, warnings). LED matrix displays. Cost ₹3-10 lakh per sign + control system.
! Inter-letter spacing: too tight reduces legibility; too loose wastes space and reduces letter-per-line capacity. 1/4 to 1/5 height is IRC 30 specification — balance between legibility and space efficiency.
! Sign placement: too close to decision point = driver can't react; too far = forgotten. IRC 35 specifies advance distances (120 m before intersection on urban, 300 m on highway).
! Signs should not be overloaded with information. '2 lines maximum' rule generally applied; more than 4 lines becomes unreadable at speed.
! Route number signs (NH shield with number): IRC 30 provides proportions. National Highway shield (white on green with NH number), State Highway shield (white on green with SH number).
! Distance signs: show kilometres remaining to next town or junction. Typically at 2 km intervals approaching major cities. Legend 200 mm letter height on highway.
! Schools, hospitals, tourist sites: special signs per IRC 35 with specific colour (yellow-orange). IRC 30 defines letter standards for these.
! Signage audit: bi-annually per CE/PWD. Check legibility (visual test from design distance), physical condition (rust, dent, sheeting degradation), positioning, mounting integrity.
! Emerging: dynamic signage via ITS — digital signs that change based on traffic conditions, weather, incidents. Integrated with urban traffic management centers.
! Autonomous vehicle recognition (Amendment No. 2, 2022): standardized symbols readable by AI/ML systems. Higher contrast, simpler fonts, clear edges. India aligning with international AV standards.
! Sign production cost: aluminium substrate ₹300-600/m²; Type III sheeting ₹500-1000/m² + letter cutting/printing; total for 600 × 600 mm sign ₹300-600 fabrication. Installation additional.