<s>
A	O
destination	B-General_Concept
sign	I-General_Concept
(	O
North	O
American	O
English	O
)	O
or	O
destination	O
indicator/destination	O
blind	O
(	O
British	O
English	O
)	O
is	O
a	O
sign	O
mounted	O
on	O
the	O
front	O
,	O
side	O
or	O
rear	O
of	O
a	O
public	O
transport	O
vehicle	O
,	O
such	O
as	O
a	O
bus	O
,	O
tram/streetcar	O
or	O
light	O
rail	O
vehicle	O
,	O
that	O
displays	O
the	O
vehicle	O
's	O
route	O
number	O
and	O
destination	O
,	O
or	O
the	O
route	O
's	O
number	O
and	O
name	O
on	O
transit	O
systems	O
using	O
route	O
names	O
.	O
</s>
<s>
The	O
main	O
such	O
sign	O
,	O
mounted	O
on	O
the	O
front	O
of	O
the	O
vehicle	O
,	O
usually	O
located	O
above	O
(	O
or	O
at	O
the	O
top	O
of	O
)	O
the	O
windshield	O
,	O
is	O
often	O
called	O
the	O
headsign	B-General_Concept
,	O
most	O
likely	O
from	O
the	O
fact	O
that	O
these	O
signs	O
are	O
located	O
on	O
the	O
front	O
,	O
or	O
head	O
,	O
end	O
of	O
the	O
vehicle	O
.	O
</s>
<s>
Several	O
different	O
types	O
of	O
technology	O
have	O
been	O
used	O
for	O
destination	B-General_Concept
signs	I-General_Concept
,	O
from	O
simple	O
rigid	O
placards	O
held	O
in	O
place	O
by	O
a	O
frame	O
or	O
clips	O
,	O
to	O
rollsigns	O
,	O
to	O
various	O
types	O
of	O
computerized	O
,	O
electronically	O
controlled	O
signs	O
,	O
such	O
as	O
flip-dot	O
,	O
LCD	B-Device
or	O
LED	O
displays	O
.	O
</s>
<s>
All	O
of	O
these	O
can	O
still	O
be	O
found	O
in	O
use	O
today	O
,	O
but	O
most	O
transit-vehicle	O
destination	B-General_Concept
signs	I-General_Concept
now	O
in	O
use	O
in	O
North	O
America	O
and	O
Europe	O
are	O
electronic	O
signs	O
.	O
</s>
<s>
In	O
the	O
US	O
,	O
the	O
Americans	O
with	O
Disabilities	O
Act	O
of	O
1990	O
specifies	O
certain	O
design	O
criteria	O
for	O
transit-vehicle	O
destination	B-General_Concept
signs	I-General_Concept
,	O
such	O
as	O
maximum	O
and	O
minimum	O
character	O
height-to-width	O
ratio	O
and	O
contrast	O
level	O
,	O
to	O
ensure	O
the	O
signs	O
are	O
sufficiently	O
readable	O
to	O
visually	O
impaired	O
persons	O
.	O
</s>
<s>
In	O
the	O
2010s	O
,	O
LED	O
signs	O
have	O
replaced	O
flip-dot	O
signs	O
as	O
the	O
most	O
common	O
type	O
of	O
destination	B-General_Concept
sign	I-General_Concept
in	O
new	O
buses	O
and	O
rail	O
transit	O
vehicles	O
.	O
</s>
<s>
For	O
many	O
decades	O
,	O
the	O
most	O
common	O
type	O
of	O
multiple-option	O
destination	B-General_Concept
sign	I-General_Concept
was	O
the	O
rollsign	O
(	O
or	O
bus	O
blind	O
,	O
curtain	O
sign	O
,	O
destination	O
blind	O
,	O
or	O
tram	O
scroll	O
)	O
:	O
a	O
roll	O
of	O
flexible	O
material	O
with	O
pre-printed	O
route	O
number/letter	O
and	O
destinations	O
(	O
or	O
route	O
name	O
)	O
,	O
which	O
is	O
turned	O
by	O
the	O
vehicle	O
operator	O
at	O
the	O
end	O
of	O
the	O
route	O
when	O
reversing	O
direction	O
,	O
either	O
by	O
a	O
hand	O
crank	O
or	O
by	O
holding	O
a	O
switch	O
if	O
the	O
sign	O
mechanism	O
is	O
motorized	O
.	O
</s>
<s>
A	O
digital	B-Device
display	I-Device
may	O
be	O
somewhat	O
less	O
readable	O
,	O
but	O
is	O
easier	O
to	O
change	O
between	O
routes/destinations	O
and	O
to	O
update	O
for	O
changes	O
to	O
a	O
transit	O
system	O
's	O
route	O
network	O
.	O
</s>
<s>
The	O
on-board	O
computer	O
is	O
normally	O
programmed	O
with	O
information	O
on	O
the	O
order	O
of	O
the	O
displays	O
,	O
and	O
can	O
be	O
programmed	O
using	O
the	O
non-volatile	B-General_Concept
memory	I-General_Concept
should	O
the	O
blind/roll	O
be	O
changed	O
.	O
</s>
<s>
These	O
buses	O
were	O
equipped	O
with	O
a	O
destination	B-General_Concept
sign	I-General_Concept
slot	O
which	O
2	O
plastic	O
destination	B-General_Concept
signs	I-General_Concept
could	O
be	O
placed	O
in	O
it	O
,	O
such	O
that	O
the	O
driver	O
could	O
press	O
a	O
button	O
to	O
flip	O
them	O
at	O
the	O
terminus	O
,	O
and	O
one	O
slot	O
at	O
the	O
front	O
,	O
side	O
and	O
back	O
of	O
the	O
bus	O
respectively	O
for	O
the	O
route	O
number	O
only	O
.	O
</s>
<s>
In	O
the	O
United	O
States	O
,	O
the	O
first	O
electronic	O
destination	B-General_Concept
signs	I-General_Concept
for	O
buses	O
were	O
developed	O
by	O
Luminator	O
in	O
the	O
mid-1970s	O
and	O
became	O
available	O
to	O
transit	O
operators	O
in	O
the	O
late	O
1970s	O
,	O
but	O
did	O
not	O
become	O
common	O
until	O
the	O
1980s	O
.	O
</s>
<s>
Another	O
technology	O
that	O
has	O
been	O
employed	O
for	O
destination	B-General_Concept
signs	I-General_Concept
is	O
the	O
split-flap	B-Device
display	I-Device
,	O
or	O
Solari	O
display	O
,	O
but	O
outside	O
Italy	O
,	O
this	O
technology	O
was	O
never	O
common	O
for	O
use	O
in	O
transit	O
vehicles	O
.	O
</s>
<s>
Such	O
displays	O
were	O
more	O
often	O
used	O
at	O
transit	O
hubs	O
to	O
display	O
arrival	O
and	O
departure	O
information	O
,	O
rather	O
than	O
as	O
destination	B-General_Concept
signs	I-General_Concept
on	O
transit	O
vehicles	O
.	O
</s>
<s>
Most	O
present-day	O
destination	O
indicator	O
signs	O
consist	O
of	O
liquid	B-Device
crystal	I-Device
display	I-Device
(	O
LCD	B-Device
)	O
or	O
light-emitting	O
diode	O
(	O
LED	O
)	O
panels	O
that	O
can	O
show	O
animated	O
text	O
,	O
colors	O
(	O
in	O
the	O
case	O
of	O
LED	O
signs	O
)	O
,	O
and	O
a	O
potentially	O
unlimited	O
number	O
of	O
routes	O
(	O
so	O
long	O
as	O
they	O
are	O
programmed	O
into	O
the	O
vehicle	O
's	O
sign	O
controller	O
unit	O
;	O
some	O
sign	O
controller	O
units	O
may	O
also	O
allow	O
the	O
driver	O
to	O
write	O
the	O
route	O
number	O
and	O
the	O
destination	O
text	O
through	O
a	O
keypad	O
if	O
required	O
)	O
.	O
</s>
<s>
Some	O
such	O
signs	O
also	O
have	O
the	O
capability	O
of	O
changing	O
on-the-fly	O
as	O
the	O
vehicle	O
moves	O
along	O
its	O
route	O
,	O
with	O
the	O
help	O
of	O
GPS	O
technology	O
,	O
serial	B-Protocol
interfaces	I-Protocol
and	O
a	O
vehicle	O
tracking	O
system	O
.	O
</s>
