Drunk and Drugged Driving Arrests Fall in Washington As Anti-Pot Group Warns That Legalization Undermines Road Safety

The anti-pot group Project SAM
claims recent data from Washington show that marijuana
legalization makes the roads more dangerous. According to State
Toxicologist Fiona Couper, the share of drivers charged with
driving under the influence of a drug whose blood tested
positive for THC, marijuana’s main psychoactive ingredient,
rose from 18.6 percent in 2012, the year that voters approved
legalization, to 24.9 percent in 2013. That’s an increase of more
than 33 percent, as Project SAM emphasizes with a scary-looking bar
graph. By comparison, the THC-positive share rose by 6.6 percent
between 2009 and 2010, rose by 4.1 percent between 2010 and 2011,
and fell by 7.9 percent between 2011 and 2012. “Even before the
first marijuana store opens in Washington, normalization and
acceptance has set in,” says Project SAM Chairman Patrick J.
Kennedy. “This is a wakeup call for officials and the public about
the dangerousness of this drug, especially when driving.”

In truth, these numbers do not tell us anything about the
dangerousness of marijuana. They could merely reflect an increase
in consumption. If more Washingtonians are smoking pot, more
drivers will test positive for THC, which does not necessarily mean
they are impaired. The cutoff for a positive test result is two
nanograms per milliliter of blood, less than half the level set by
Washington’s new per
se standard for DUID, which itself is not necessarily a good
indicator of impairment.

Assuming that marijuana consumption in Washington rose between
2012 and 2013, can that increase be attributed to legalization?
Supplying recreational marijuana remains illegal until the first
state-licensed shops open later this year, and I-502, Washington’s
legalization measure, does not allow people to grow their own. But
it has already eliminated penalties for possession of up to an
ounce by adults 21 or older, which may have had an impact on
consumption.

A key question in assessing the impact of legalization on road
safety is whether more pot smoking will mean less drinking. If so,
the net result could be fewer traffic fatalities, even if there is
an increase in the number of stoned drivers, because alcohol has a
more dramatic effect on driving ability than marijuana does.
A study published
last year by the Journal of Law &
Economics found that adoption of medical marijuana laws
is associated with a decline in traffic fatalities,
possibly because of such a substitution effect.

According to data from the Washington State Patrol, the number
of drunk driving arrests fell from 17,382 in 2012 to 15,401 in
2013, an 11 percent drop. By comparison, the number of drunk
driving arrests fell by 2 percent between 2009 and 2010, stayed
about the same between 2010 and 2011, and fell by 6 percent between
2011 and 2012. Although the drop in drunk driving arrests after
marijuana legalization looks unusually large, it should be
interpreted with caution, since the number of arrests is partly a
function of enforcement levels, which depend on funding and
staffing. Still, the drop is consistent with substitution of
marijuana for alcohol.

The number of DUID arrests by state police also fell after
legalization, from 1,621 in 2012 to 1,357 in 2013, a 16 percent
drop. By comparison, DUID arrests stayed about the same from 2009
to 2010, rose by 12 percent from 2010 to 2011, and fell by 7
percent from 2011 to 2012. Again, enforcement levels might have
something to do with the drop. But these numbers do not suggest
that Washington’s highways are awash with dangerously stoned
drivers.