What is an enhanced taxiway centerline and what does it warn pilots about?

2-3-4. Taxiway Markings
a. General. All taxiways should have centerline markings and runway holding position markings whenever
they intersect a runway. Taxiway edge markings are present whenever there is a need to separate the taxiway from
a pavement that is not intended for aircraft use or to delineate the edge of the taxiway. Taxiways may also have
shoulder markings and holding position markings for Instrument Landing System (ILS) critical areas and
taxiway/taxiway intersection markings.
REFERENCE-
AIM, Para 2-3-5, Holding Position Markings.
b. Taxiway Centerline.
1. Normal Centerline. The taxiway centerline is a single continuous yellow line, 6 inches (15 cm) to 12
inches (30 cm) in width. This provides a visual cue to permit taxiing along a designated path.  Ideally, the aircraft
should be kept centered over this line during taxi. However, being centered on the taxiway centerline does not
guarantee wingtip clearance with other aircraft or other objects.
2. Enhanced Centerline. At some airports, mostly the larger commercial service airports, an enhanced
taxiway centerline will be used. The enhanced taxiway centerline marking consists of a parallel line of yellow
dashes on either side of the normal taxiway centerline. The taxiway centerlines are enhanced for a maximum of
150 feet prior to a runway holding position marking. The purpose of this enhancement is to warn the pilot that
he/she is approaching a runway holding position marking and should prepare to stop unless he/she has been
cleared onto or across the runway by ATC. (See FIG 2-3-8.)
c. Taxiway Edge Markings. Taxiway edge markings are used to define the edge of the taxiway. They are
primarily used when the taxiway edge does not correspond with the edge of the pavement. There are two types
of markings depending upon whether the aircraft is supposed to cross the taxiway edge:
Airport Marking Aids and Signs 2-3-7

AIM 2/20/25
1. Continuous Markings. These consist of a continuous double yellow line, with each line being at least
6 inches (15 cm) in width spaced 6 inches (15 cm) apart. They are used to define the taxiway edge from the
shoulder or some other abutting paved surface not intended for use by aircraft.
2. Dashed Markings. These markings are used when there is an operational need to define the edge of a
taxiway or taxilane on a paved surface where the adjoining pavement to the taxiway edge is intended for use by
aircraft (for example, an apron). Dashed taxiway edge markings consist of a broken double yellow line, with each
line being at least 6 inches (15 cm) in width, spaced 6 inches (15 cm) apart (edge to edge). These lines are 15
feet (4.5 m) in length with 25 foot (7.5 m) gaps. (See FIG 2-3-9.)
d. Taxi Shoulder Markings. Taxiways, holding bays, and aprons are sometimes provided with paved
shoulders to prevent blast and water erosion. Although shoulders may have the appearance of full strength
pavement, they are not intended for use by aircraft and may be unable to support an aircraft. Usually the taxiway
edge marking will define this area. Where conditions exist such as islands or taxiway curves that may cause
confusion as to which side of the edge stripe is for use by aircraft, taxiway shoulder markings may be used to
indicate the pavement is unusable. Taxiway shoulder markings are yellow. (See FIG 2-3-10.)
2-3-8 Airport Marking Aids and Signs

2/20/25 AIM
FIG 2-3-6
Markings for Blast Pad or Stopway or Taxiway Preceding a Displaced Threshold
Airport Marking Aids and Signs 2-3-9

 AIM 2/20/25
FIG 2-3-7
Markings for Blast Pads and Stopways
2-3-10 Airport Marking Aids and Signs

2/20/25 AIM
FIG 2-3-8
Enhanced Taxiway Centerline
FIG 2-3-9
Dashed Markings
DOUBLE
YELLOW
LINES
TAXIWAY EDGE TAXIWAY EDGE
MARKINGS MARKINGS
CONTINUOUS DASHED
e. Surface  Painted Taxiway Direction Signs. Surface painted taxiway direction signs have a yellow
background with a black inscription, and are provided when it is not possible to provide taxiway direction signs
at intersections, or when necessary to supplement such signs. These markings are located adjacent to the
centerline with signs indicating turns to the left being on the left side of the taxiway centerline, and signs
indicating turns to the right being on the right side of the centerline. (See FIG 2-3-11.)
Airport Marking Aids and Signs 2-3-11

 AIM 2/20/25
FIG 2-3-10
Taxi Shoulder Markings
RUNWAY
YELLOW STRIPES
PAVEMENT EDGE
TAXIWAY EDGE
MARKINGS
f. Surface Painted Location Signs. Surface painted location signs have a black background with a yellow
inscription. When necessary, these markings are used to supplement location signs located along side the taxiway
and assist the pilot in confirming the designation of the taxiway on which the aircraft is located. These markings
are located on the right side of the centerline. (See FIG 2-3-11.)
g. Geographic Position Markings. These markings are located at points along low visibility taxi routes
designated in the airport's Surface Movement Guidance Control System (SMGCS) plan. They are used to
identify the location of taxiing aircraft during low visibility operations. Low visibility operations are those that
occur when the runway visible range (RVR) is below 1200 feet (360m). They are positioned to the left of the
taxiway centerline in the direction of taxiing. (See FIG 2-3-12.) The geographic position marking is a circle
comprised of an outer black ring contiguous to a white ring with a pink circle in the middle. When installed on
asphalt or other dark-colored pavements, the white ring and the black ring are reversed (i.e., the white ring
becomes the outer ring and the black ring becomes the inner ring). It is designated with either a number or a
number and letter. The number corresponds to the consecutive position of the marking on the route.
Airport Marking Aids and Signs2-3-12

2/20/25 AIM
FIG 2-3-11
Surface Painted Signs
Airport Marking Aids and Signs 2-3-13

AIM 2/20/25