As the City of Seattle is set to test lowering speed limits on residential streets to 20 mph (from 25 mph), it’s important to understand why they’re doing it. Is this about safety or getting people out of cars?

Seattle Department of Transportation argues this is about improving “safety and livability in Seattle neighborhoods.” But it’s also a prelude to lowering arterial streets to 30 mph, as well. SDOT isn’t promoting this very actively, but it’s hidden in their 76-page Move Seattle plan. It’s also part of a bigger, unachievable (but laudable) goal of ending all traffic deaths and serious injuries by 2030.

This brings up two questions: 1) does lowering the speed limit actually lead to safer streets; and 2) are there ulterior motives behind this plan?

On the surface, you would think it would lead to safer streets. As SDOT Director Scott Kubly says, it’s all about “Newtonian physics” – if you’re driving really fast and you hit an object, you cause lots of damage; if you’re slower, you cause less damage. Fair enough. But let’s look to our weird neighbors to the south.

Related: Oppose Seattle transportation plans? You want people dead

Portland has lower speeds than Seattle. The speed limit in business districts is just 20 mph; in residential zones, it’s 25 mph. Yet they have a higher percentage of roadway fatalities than Seattle, according to their latest data. In 2014, for example, they had 15 pedestrian fatalities. Seattle had 10.

Seattle has, in fact, experienced a decline in traffic collisions every year since 2005 according to the latest published SDOT data. The drop is remarkable and it continues to decline – all that without any changes in traffic speeds, yet with more people biking and walking. Pedestrian-involved collision rates have declined since 2005. Fatal pedestrian-involved collisions have fallen since 2005. Even the bicycle collision rate is down since 2005, though there was a slight increase from 2012 to 2013.

Now, this doesn’t prove lowering speed limits won’t lead to fewer fatalities and collisions. London saw reduced casualties when they lowered their speed limits and that’s worth noting. But it’s also worth noting fatalities are caused by more than just speed limits: driver education, lack of proper lighting, driver behavior (such as DUI), poor infrastructure, poorer engineering, etc.

Related: West Seattle residents fighting shoddy SDOT bike lane study

While there’s no doubt SDOT and Mayor Murray want to see fewer fatalities (everyone does), the truth is lowering speed limits is part of a bigger strategy to get drivers out of their cars, and onto bikes, Metro, and foot. They’re doing what Edinburgh, Scotland is doing, only Seattle isn’t being honest. From Next City (in part):

As more U.S. cities embrace the Vision Zero approach to curtailing traffic and ensuring pedestrian safety, there’s plenty of compelling data in favor of slow roads coming out of Edinburgh, Scotland. The numbers show how lower speed limits can change drivers’ attitudes about bicyclists – and even let city-dwellers breathe a bit easier thanks to air quality improvement.

…After three years of planning, public engagement and pilot projects […] the new strategy is explicitly about encouraging people to bike or walk, rather than drive.

There is no doubt the city is actively trying to make driving as unappealing as possible, in favor of installing bike lanes no one wants or needs (a perfect example of this is happening in West Seattle). And even though there is low demand for bike sharing for long distances, the city is trying to massively expand the Pronto bike sharing program. They hope to get the expansion going, then use it as an excuse to create more bike lanes.

I don’t dismiss the safety concerns of SDOT, but the real reason behind this plan is to get you out of the car. They just use the safety concerns as a shield from criticism (just remember: whenever you question their plans on this, they will imply that if you don’t support them, you actually want people to die from collisions). So my question for SDOT and the mayor is: why not just fully embrace your privately-held end goal of getting people out of cars as much as possible? Is it because that’s a goal that we might reject? (I’m not convinced the city would reject that.)