Is “Twenty Is Plenty” A Good Idea for Greenville, South Carolina?

By Dom Nozzi

Greenville, South Carolina – where I now live – had some of its bicycling and walking advocates consider adopting a “Twenty (mph) Is Plenty” program to enhance walking and cycling safety.

I was asked what I thought of the idea.

I responded by saying that when I served on the Boulder CO Transportation Advisory Board, one of the agenda items that came before us was a “20 Is Plenty” campaign, which was ultimately approved by Council.

I expressed serious reservations at the time.

While it is extremely important to effectively slow motor vehicle speeds, revising speed limit signs down to 20 mph does almost nothing to meaningfully slow vehicle speeds because what controls vehicle speeds is almost entirely based on the design speed of streets. Almost no motorist pays any attention to signs. Lowering limits on signs, therefore, can be seen as little more than ineffective lip service.

Cities like Boulder and Greenville have an enormous number of streets with design speeds far above 20 mph, which powerfully induces excessive speeds by vehicles.

An important concern here is that a great many might conclude that “our work is done” on slowing vehicles, simply because we’ve lowered limits on signs. Such people don’t realize that work has not even started if we simply change speed limit signs.

Another moderately legitimate argument against lowering limits on signs without lowering street design speeds is that this is an underhanded way to allow the City to collect revenue, as the lower limits on signs will — due to higher design speeds for streets — lead to a jump in speeding tickets.

A counterargument to my “lip service” concerns is that our community — by lowering limits on signs — has sent a message to city government and the South Carolina Department of Transportation (SCDOT) that our community strongly desires slower vehicle speeds. And we want the City and SCDOT to start getting serious about designing streets for slower speeds.

Effective tools?

Much more on-street parking. On-street parking provides a quick and low-cost calming tool for our community. Such parking provides a safety and convenience boost for homes, a way to reduce noise pollution, a way to reduce the need for large asphalt off-street parking lots, and a way to provide a financial boost for small retailers.

Road and intersection diets (ie, removal of excessive travel and turn lanes).

Landscaped bulb-outs (to reduce the width and crossing distance of streets).

“Woonerfs” (Dutch “living street” design — see Wall St in downtown Asheville NC).

Converting one-way streets back to two-way operation.

Replacing stop signs and traffic signals with traffic circles and roundabouts.

Installing large canopy street trees.

Replacing the several miles of dangerous “continuous left-turn lanes” throughout Greenville’s town center with raised medians.

Reducing the height of street lights, signs, and traffic signals.

By the way, I believe it is important that we actively oppose the use of speed humps for vehicle speed reduction (an all-too-common calming method that has important downsides). This City needs to remove existing humps, as they are a noise pollution problem, punish even slower speed vehicles, are terrible for cyclists, and are a serious problem for emergency vehicle response. Removing the humps needs to be coupled — simultaneously — with installation of preferable tools such as methods I mention above.

It must also be noted that humps give traffic calming efforts a black eye, as a great many citizens are understandably highly annoyed by humps, and that annoyance is often generalized to apply to all forms of calming.

In sum, I’m happy to see the widespread interest in slower speeds for vehicles. I don’t necessarily oppose a “20 Is Plenty” effort to reduce limits on signs. But we need to be careful about strategies to effectively achieve that exceptionally important objective of slowing vehicles, and not just pay lip service to our doing that.

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