We propose here a simple black-hole analog in vehicular-traffic dynamics. The corresponding causal diagram is determined by the propagation of the tail light flashes emitted by a convoy of cars on a highway. In addition to being a new black-hole analog, this illustrates how causal diagrams, so common in general relativity, may be useful in areas as unexpected as vehicular-traffic dynamics.

1.
V.
Moncrief
, “
Stability of stationary, spherical accretion onto a Schwarzschild black hole
,”
Astrophys. J.
235
,
1038
1046
(
1980
).
2.
W. G.
Unruh
, “
Experimental black hole evaporation
,”
Phys. Rev. Lett.
46
,
1351
1353
(
1981
).
3.
S. W.
Hawking
, “
Black hole explosions?
,”
Nature (London)
248
,
30
31
(
1974
);
S. W.
Hawking
, “
Particle creation by black holes
,”
Commun. Math. Phys.
43
,
199
220
(
1975
).
4.
M.
Visser
, “
Acoustic black holes: Horizons, ergospheres, and Hawking radiation
,”
Class. Quantum Grav.
15
,
1767
1791
(
1998
).
5.
C.
Barceló
,
S.
Liberati
, and
M.
Visser
, “
Analogue gravity
,”
Living Rev. Relativity
14
,
3
(
2011
).
6.
M. L. L.
Iannini
and
R.
Dickman
, “
Kinetic theory of vehicular traffic
,”
Am. J. Phys.
84
,
135
145
(
2016
).
7.
G.
Johansson
and
K.
Rumar
, “
Drivers' brake reaction times
,”
Human Factors
13
,
23
27
(
1971
).
8.
D.
Helbing
, “
Traffic and related self-driven many-particle systems
,”
Rev. Mod. Phys.
73
,
1067
1141
(
2001
).
9.
R. M.
Wald
,
General Relativity
(
University of Chicago Press
,
Chicago
,
1984
).
10.
A. S.
Eddington
, “
A comparison of Whitehead's and Einstein's formulae
,”
Nature
113
,
192
(
1924
).
11.
D.
Finkelstein
, “
Past-future asymmetry of the gravitational field of a point particle
,”
Phys. Rev.
110
,
965
967
(
1958
).
12.
R. J.
Adler
, “
Six easy roads to the Planck scale
,”
Am. J. Phys
78
,
925
932
(
2010
).
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