Taxiway & Standard
Straight and curve spacing databases are kept separate per standard — never one universal value.
Changing the input unit converts the lengths, segment list and measured coordinates already typed (angles are unchanged) and re-fills the standard’s spacing limits.
Documentation only in this calculator — the centreline alignment does not depend on width (see Calculator #08 for edge-light geometry).
Documentation only — the actual geometry is defined by the segment list below.
If "Yes", the segment list should include at least one runwayentry segment — the calculator does not continue normal centreline spacing blindly through a runway interface.
Spacing Criteria
Selects the straight-section limit and the radius-based curve limit pre-filled below. Changing it re-fills the spacing fields.
Rule note
Nominal design spacing — intervals are calculated and redistributed uniformly rather than dividing by Smax directly. Worked example: L = 487 m and Sdesign = 30 m give N = 17 intervals (18 lights including both ends) and Sactual = 28.65 m (see Methodology).
Rule note
Pre-filled from the standard and the RVR band selected above: ICAO 30 m (15 m below 350 m RVR); FAA 100 ft (50 ft below 1,200 ft RVR). ICAO permits up to 60 m only where meteorological conditions give adequate guidance, and requires closer spacing on short straights — confirm against the approved project specification. Left blank, the straight-spacing check is skipped.
Nominal spacing along the arc — lights follow the actual curve, not a straight chord. Pre-filled with the radius-based limit for the default radius class (ICAO 7.5 m for radius up to 400 m; FAA 25 ft, or 12.5 ft below 1,200 ft RVR, for radius under 400 ft) — raise it only where every curve radius allows a coarser pitch.
Rule note
For ICAO / DGCA and FAA the limit is taken automatically from the standard's radius table for every curve segment (ICAO: radius up to 400 m 7.5 m, 401–899 m 15 m, 900 m or more 30 m, never above 15 m below 350 m RVR; FAA AC 150/5340-30J Table 4-1: 75–399 ft 25 ft / 12.5 ft, 400–1,199 ft 50 ft / 25 ft, 1,200 ft or more 100 ft / 50 ft for RVR above / below 1,200 ft). A value entered here is used only where it is stricter than the table. For “Project Specification” this value is the limit.
Used for automatic duplicate-fixture detection and the existing-installation centreline-alignment check below.
Coordinate System Setup
Rule note
Any local project coordinate system works — the schedule below reports relative X,Y, not survey grid coordinates, unless X₀/Y₀ are entered as real grid values.
Centreline Geometry — Segments
One segment per line, in order along the taxiway: straight,<length>[,<spacing>] · curve,<radius>,<angle deg>,<left|right> · intersection,<length> · runwayentry,<length>. The optional third value overrides the design spacing for that segment — use it to model the closer spacing that ICAO asks to continue 60 m before and after a curve (for example straight,60,7.5) or the closer-spaced lights FAA AC 150/5340-30J calls for on the straights before and after a curve. Intersection and runway-entry segments still generate lights (tagged with their own function) — they are not excluded like taxiway edge lights, but are flagged for layout review since the exact configuration is project-specific.
Rule note
Default example: 300 m straight → 100 m-radius curve turning left through ≈120 m of arc → 400 m straight, reproducing the S1/C1/S2 conceptual example from the design brief.
Duplicate-Position Handling
Rule note
This engine automatically flags any two generated positions on this alignment closer than tolerance T (see below). Where a position also coincides with a fixture from a different taxiway's calculator run (a true intersection between two alignments), enter that count here — full cross-alignment 2D matching is outside this single-run engine's scope.
Report details
Segment schedule
Segment Schedule
Qphysical = Qstraight + Qcurve + Qintersection + Qenhanced − Qduplicate, not a single length ÷ spacing shortcut.
Light schedule & BOQ
Full Light Schedule (Coordinates)
BOQ Summary
| Component | Basis | Quantity |
|---|---|---|
| Normal centreline lights | Straight and curve positions outside the enhanced zone | — |
| Enhanced centreline lights | Positions inside the enhanced zone (re-classified, not added) | — |
| Special / intersection lights | Intersection + runway lead-on/off positions | — |
| Duplicate positions removed | Auto-detected + manual entry | — |
| Total physical fixtures | — |
Build-up
Check measured fixture positions against Smax. The standard, units and spacing limits come from the Calculate tab.
Existing-Installation Inspection (optional)
How This Calculator Works
Geometry → segments → applicable rule → positions → validation → quantity. The centreline is never reduced to "length ÷ 30 m" as a final result.
Straight-section rule
Worked example: L = 487 m, Sdesign = 30 m → N = ⌈487/30⌉ = 17 intervals (18 lights) → Sactual = 487/17 = 28.65 m, uniformly redistributed rather than leaving an irregular final gap.
Centreline coordinates — straight
P0 is the segment start point, u is the centreline unit vector (heading), S is the actual spacing. This calculator generates the full light schedule (chainage, X, Y) from this formula rather than reporting a count alone.
Curve geometry & angular position
Each light's angular position θi = θ0 + iΔθ is calculated from the curve centre, so generated lights follow the actual centreline arc — never approximated by straight chord segments.
Chord vs. arc distance
These are not the same value and this calculator does not confuse them: design spacing along a curve is generated and checked on the arc-length basis (Darc), consistent with how the curve is walked to generate positions.
Colour / function logic
Function is classified automatically from the segment type — taxiway centreline, intersection, runway lead-on/lead-off, or enhanced centreline — rather than left as an arbitrary user-selected colour. The applicable colour is reported against the selected standard; the exact ICAO/FAA configuration table for every function is not hard-coded and should be confirmed against the project standard.
Duplicate-fixture control
Every generated position on this alignment is automatically checked pairwise against tolerance T — where DAB < T, the calculator flags a potential duplicate rather than silently counting two fixtures. True duplicates arising from a second, separately-run taxiway alignment crossing this one are outside a single-run engine's scope and are captured via the manual entry field instead.
Existing-installation & centreline alignment
Measured spacing is checked against the applicable Smax; each measured point's perpendicular deviation from the nearest design segment (straight or curve) is checked against the positional tolerance T, reported as centreline alignment PASS/FAIL.
Standard-specific spacing database
| Standard | Straight | Curve |
|---|---|---|
| ICAO Annex 14 | 30 m (15 m below 350 m RVR) | Radius table: ≤ 400 m 7.5 m · 401–899 m 15 m · ≥ 900 m 30 m (never above 15 m below 350 m RVR) |
| FAA AC 150/5340-30J | 100 ft (50 ft below 1,200 ft RVR) | Radius table (Table 4-1): 75–399 ft 25 ft · 400–1,199 ft 50 ft · ≥ 1,200 ft 100 ft (half those values below 1,200 ft RVR) |
| DGCA / Indian implementation | As ICAO — confirm against current DGCA CAR / AIP | As ICAO radius table |
The straight-section limits are pre-filled as editable defaults and drive the pass/fail check. On curves each segment is checked against the radius-based limit above, so a tight lead-on / lead-off curve and a gentle apron curve are not held to the same figure. ICAO also recommends continuing the curve spacing 60 m before and after a curve and FAA AC 150/5340-30J asks for closer-spaced lights on the straights either side of a curve (confirm the number and pitch in the AC); model it with the optional segment spacing, e.g. straight,60,7.5.
Engineering quantity formula
Preferable to Q = L/S because a real taxiway is rarely one simple straight line — each segment and special zone follows its own rule.
Runway interface
A centreline approaching a runway is treated as a distinct segment type (runwayentry) rather than continuing the normal taxiway-centreline spacing through the interface. Its exact configuration (lead-on/lead-off spacing, colour transition point) is project/standard-specific and flagged for review rather than assumed.
What this calculator does not do
It applies the radius-based ICAO/FAA curve-spacing limits but does not maintain the figure-level configuration database, does not add the curve lead-in / lead-out spacing automatically (use the optional segment spacing), does not resolve the detailed runway-entry/exit configuration, and does not perform true 2D matching between two independently-run taxiway alignments (only this alignment's self-duplicates are automatic). Straight/curve geometry, coordinate generation, and segment-level quantity are fully calculated; exact figure-level configuration must be confirmed against the approved layout.
Taxiway Centreline Lights: Frequently Asked Questions
Quick answers on how the calculator generates taxiway centreline lighting.
What does the Taxiway Centreline Light Spacing & Quantity calculator do?
It walks the taxiway alignment segment by segment and generates an actual X,Y position and chainage for every centreline light. It handles straights and curves, an enhanced-centreline zone, intersections and runway interfaces, flags duplicate fixtures, and can check an existing installation for spacing and alignment.
How is straight-section spacing worked out?
N = ⌈L ÷ S_design⌉ intervals, then S_actual = L ÷ N, so the lights are spread uniformly instead of leaving an irregular last gap. For L = 487 m and S_design = 30 m, N = 17 intervals (18 lights) and S_actual = 28.65 m.
How are lights positioned on a curve?
Each light's angle is measured from the curve centre, with Δθ = θ ÷ N, so lights follow the true arc and not straight chords. Arc distance is D_arc = R × Δθ and chord distance is D_chord = 2R × sin(Δθ/2). They differ, and spacing along a curve is generated and checked on the arc-length basis.
What straight-section spacing limits are pre-filled?
ICAO 30 m (15 m where RVR is below 350 m) and FAA 100 ft (50 ft where RVR is below 1,200 ft). The DGCA option follows ICAO, so confirm it against the current DGCA CAR or AIP. These are editable defaults. Curve limits come from each standard’s radius table and are checked per curve segment: ICAO 7.5 m up to 400 m radius, 15 m from 401 to 899 m and 30 m from 900 m (never above 15 m below 350 m RVR); FAA 25 ft for 75 to 399 ft radius (12.5 ft below 1,200 ft RVR), 50 ft for 400 to 1,199 ft and 100 ft above that.
How does the enhanced centreline zone work?
You enter a zone length and choose whether it sits at the start or the end of the segment list, so it can be placed at the runway end. Centreline positions inside it are re-classified as enhanced, for example alternating green and yellow, and counted once, not added on top of the normal lights. The FAA enhanced taxiway centerline is a pavement marking, so this zone models alternating green and yellow centreline lights only.
How are intersections and runway entries treated?
Intersection and runwayentry segments still generate lights, tagged with their own function, but are flagged for layout review because the exact configuration is project-specific. The calculator does not carry normal centreline spacing blindly through a runway interface.
How are duplicate fixtures detected?
Any two generated positions on the same alignment that are closer than the positional tolerance T (0.15 m by default) are flagged as a potential duplicate. Duplicates caused by a separate taxiway alignment crossing this one are outside a single-run engine, so you enter them in the manual field.
How does the existing-installation check work?
You enter measured x,y coordinates. The distance between consecutive fixtures is checked against the applicable maximum spacing, and each point's perpendicular deviation from the nearest design segment, D_⊥, is checked against the tolerance T. The result is reported as spacing and centreline alignment pass or fail.