Chapter 3G. Islands
Section 3G.01 General
Chapter 3G addresses the characteristics of islands as traffic-control
devices. Criteria for the design of islands are set forth in "A
Policy on Geometric Design of Highways and Streets" (see Section
An island for traffic control purposes shall be the defined area
between traffic lanes for control of vehicular movements or for
pedestrian refuge. Within an intersection area, a median or an outer
separation shall be an island.
An island may be designated by pavement markings, channelizing devices,
curbs, pavement edges, or other devices.
Section 3G.02 Approach-End
The ends of islands first approached by traffic should be preceded
by a gradually diverging marking on the roadway surface, to guide
vehicles into desired paths of travel along the island edge.
Approach-end markings that can be readily crossed even at considerable
speed may contain slightly raised (usually less than 25 mm (1 in)
high) sections of coarse aggregate or other suitable materials to
create rumble sections that provide increased visibility of the
marked areas and that produce an audible warning to road users traveling
Rumble strips or other devices, when used in advance of islands
having raised curbs, shall not be placed in such a manner as to
constitute an unexpected obstacle.
Bars or buttons should not project more than 25 to 75 mm (1 to 3
in) above the pavement surface and should be designed so that any
wheel encroachment within the area will be obvious to the vehicle
operator, but will not result in loss of control of the vehicle.
Bars or buttons may be preceded by rumble sections, or their height
may be gradually increased as approached by traffic.
Pavement markings may be used with raised bars to
better designate the island area.
Section 3G.03 Island
Markings, as related to islands, shall consist only of pavement
and curb markings, object markers, and delineators.
On the approach to islands, the triangular neutral
area in advance of the end of the island shall include pavement
markings as described in Section
As indicated in Section 3G.02, rumble
sections, or other similar traffic control designs which contrast
with the pavement surface, may also be applied in the triangular
neutral area in advance of the end of an island.
When raised bars or buttons are used in these neutral areas, they
should be marked with white or yellow retroreflective materials,
as determined by the direction or directions of travel they separate.
Section 3G.04 Island
Islands outlined by curbs or pavement markings should be marked
with retroreflective white or yellow material as determined by the
direction or directions of travel they separate (see Section
The retroreflective area should be of sufficient
length to denote the general alignment of the edge of the island
along which vehicles travel, including the approach nose, when viewed
from the approach to the island.
On long islands, curb retroreflection may be discontinued such that
it does not extend for the entire length of the curb, especially
if the island is illuminated or marked with delineators or edge
Section 3G.05 Island
Object markers may be installed alone or in combination with signs
(such as KEEP RIGHT, KEEP LEFT, double arrows, or guide signs) located
within the island.
Section 3G.06 Island
Delineators installed on islands shall be the same colors as the
related edge lines except that, when facing wrong-way traffic, they
shall be red (see Section 3D.03).
Each roadway through an intersection shall be
considered separately in positioning delineators to assure maximum
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