Geometric Design of Taxiway

Speed of an aircraft on runway is relatively faster than the speed on taxiway. Thus design standards, for a taxiway is not as rigid as they are for runway.

The geometric design standards of taxiway are:

(i) Length of taxiway: It should be short as it will save fuel consumption. There is no specific recommendation for length.

(ii) Width of taxiway: Width of taxiway is lesser than that of runway because speed at taxiway is lower and aircraft is not airborne. Normally it varies between 7.5 m to 22.5 m.

(iii) Width of Safety Area: It includes partially paved shoulders on either side plus the area that is graded and drained.

(iv) Longitudinal Gradient

•  Steeper gradient demands greater fuel consumption, so level taxiways are more desirable.
• ICAO recommends that maximum longitudinal gradient should be 1.5% for A and B types and 3% for other types of airports.

(v) Transverse gradient:  It is provided for quick drainage. Maximum transverse gradient is taken 1.5% for A, B and C types and 2% for other types of airports.

(vi) Rate of change of longitudinal gradient: ICAO recommends that maximum rate of change of slope in longitudinal direction 1% per 30 m length of vertical curve for A, B and C types and 1.2% in 30 m length for D and E types of airports.

(vii) Sight distance: Since speed on taxiway is slower than runway so smaller sight distance is required comparatively. ICAO recommends that

(a) For A, B, C type of airport, surface of taxiway should be visible from 3 m height for 300 m distance.

(b) For D, E type of airport, surface of taxiway should visible from 2.1 m height for 250 m distance.

(viii) Turning radius

• It is provided to change the direction of aircraft path a horizontal curve is required.
• The curve is so designed that aircraft can negotiate it without reducing speed significantly.
• Circular curve of large radius is preferred.

Note:

• For large subsonic jet R_min = 120 m. (for any value of speed)
• For supersonic transport, R_min = 180 m (for any value of speed)

• According to Horonjeff, the radius of taxiway should be decided such that the distant of the oleo strut of the nearby main gear is not less than 6 m from the pavement edge.
• According to Horonjeff, we have

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