The Effects of Commercial Electronic Variable Message Signs ...

Method Ref. # Advantages Disadvantages
1.2.5 Scenario: natural route
and trip purpose; uses own
vehicle
1.3 Retrospective database:
fatal, injury, property damage
79, 78,
64, 42
87, 49,
128,
14, 58,
1.3.1 Before-after study 158, 1,
130
1.3.2 Before-after study with
control
Mostly natural experimental
context; uses own or
borrowed vehicle.
Directly related to ultimate
goal.
54
Participant aware of test status;
may be injured or killed; vehicle
may be damaged or destroyed;
expensive.
Crashes are rare events; difficult
to estimate.
Most common study type. No control site; regression
toward mean.
120 Control adds rigor. Regression toward mean.
1.3.3 Before-after-before study More convincing causal
effect.
1.3.4 Regression model Directly account for multiple
factors.
1.3.5 Empirical Bayes Control for regression toward
mean.
1.3.6 Full Bayes More complete treatment of
conditional probabilities.
2.0 Crashes: Laboratory
2.1 Driving simulator
2.1.1 Participant: selected,
sampled
2.1.2 Experimenter: remotely
present, unobtrusive
observation
2.1.3 Stimuli: simulated,
artificial; consistent, controlled
Regression toward mean.
Large amounts of data on many
variables.
More complicated statistical
model.
Not widely used.
70 Know participant sample. Possible sampling bias.
70 More experimenter control. Possible artificial participant
behaviors.
70 Extremely repeatable
stimulus conditions.
Artificial stimuli; hard to
simulate conspicuity and
legibility.