The Impact of Severe Weather on Traffic Volume

When severe weather impacts population centers, normal activities are often disrupted – including travel plans.  However, it is largely unknown how the type, timing, and location of severe weather impact traffic patterns.  Since the probability of traffic jams in advance of severe storms is increasing, this kind of information is becoming increasingly important.  Urban areas continue to expand, leading to an increase in the areal extent of traffic jams.  As a result, the risk to motorists is also increasing: vehicles are poor shelters, and a growing number of them are becoming exposed to severe weather.  This disastrous potential was dramatically demonstrated on 31 May 2013, when thousands of Oklahoma City (OKC) motorists were stranded in traffic jams in the path of a tornadic supercell.

In this study, the effect of severe weather forecasts and warnings on traffic patterns in the OKC metropolitan area is examined.  Using traffic data from the Oklahoma Department of Transportation, several severe weather events are investigated including: the 24 May 2011 tornado outbreak, 31 May 2013 El Reno tornado, and the 26 April 2016 tornado non-event.  Warning type (severe thunderstorm vs. tornado), lead time, and storm proximity are compared to traffic volume.  Results suggest that traffic volume is significantly affected by severe storms – in proportion to pre-storm weather awareness, forecast threat magnitude, and the certainty of the threat.