In 2015, the City of Portland adopted Vision Zero's objective of eliminating transportationrelated fatalities and serious injuries. Speed, through analysis of crash data, was determined to be a contributing factor in 47% of the fatal crashes observed in Portland between 2004-2013 (City of Portland, 2016). Additionally, it is well-established that higher motor vehicle speeds result in more serious outcomes for the vulnerable road user, and the severity of an injury exponentially increases with speeds (Tefft, 2013). Thus, one of the pillars in the Vision Zero Action Plan is reductions in motor vehicle speeds. The Portland City Council approved an ordinance reducing the speed limit on all residential streets to 20 mi/hr in January 2018. A residential street is a street that is in a residence district according to ORS 801.430 and has a statutory speed limit. Federally classified collectors and arterials are excluded. The 20 mi/hr speed limit went into effect on April 1, 2018. The city installed new speed limit signs and updated existing signs to over the period of February 2018 to May 2019. The final 20 mph sign installation increased the number of residential speed limit signs from fewer than 1,000 signs to more than 2,000. An educational and awareness campaign “20 Is Plenty” was also conducted. As part of the effort, nearly 7,000 yard signs were distributed to residents. Figure 1 shows a photo of yard signs and speed limit signs at a press event. The objective of this study is to determine if there was a change in observed speeds of vehicles following the residential speed limit reduction from 25 to 20 mi/hr. The data used for this analysis was before and after observations of vehicle speeds collected by pneumatic tube traffic counters before and after the speed limits were changed.