1.0Sightline Institutehttps://www.sightline.orgClark Williams-Derryhttps://www.sightline.org/profile/clark-williams-derry/Traffic Forecasting: A Blast from the Past - Sightline Instituterich600338<blockquote class="wp-embedded-content" data-secret="HWnBgmCY1O"><a href="https://www.sightline.org/2012/06/25/traffic-forecasting-a-blast-from-the-past/">Traffic Forecasting: A Blast from the Past</a></blockquote><iframe sandbox="allow-scripts" security="restricted" src="https://www.sightline.org/2012/06/25/traffic-forecasting-a-blast-from-the-past/embed/#?secret=HWnBgmCY1O" width="600" height="338" title="“Traffic Forecasting: A Blast from the Past” — Sightline Institute" data-secret="HWnBgmCY1O" frameborder="0" marginwidth="0" marginheight="0" scrolling="no" class="wp-embedded-content"></iframe><script type="text/javascript">
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https://www.sightline.org/wp-content/uploads/2012/06/1991-traffic-forecast-manual-chart.png685666Looking through an old WSDOT traffic forecasting manual, Sightline intern Alex Broner came across this gem, illustrating the standard practices of the traffic engineering profession 20 years ago: To calculate [traffic] growth, a simple linear regression technique is used to fit a straight line through historical traffic volumes on roads containing projects that do not add lanes. A straight line has proven to be the best fit for predicting future volumes for areas not subject to significant changes in population or employment growth. To confirm that linear growth should be used, the data are plotted on graph paper and examined for evidence of linear stability. A straight line is then fitted to the stable portion of the graph, and the slope is determined. Stripping away all the math-speak, the meaning of the passage is clear: traffic volumes always grow.