Quick-Build 102

(Above) Families and neighbors of Barrio Blue Moon help implement a quick-build traffic circle in October 2022.

Part II: Types of treatments and their implementation

Last month we did a primer on quick-builds, giving an overview on what they are and why they exist. This month we’re taking a deeper dive, looking at two different kinds of quick-build projects that we’ve utilized in Tucson and their function in helping calm traffic to enhance safety.

Traffic circles

One of the most consistent concerns we hear from neighborhoods across Tucson is about traffic speeding through residential streets. In a lot of cases, neighborhood streets provide convenient cut-throughs when traffic is backed up on larger streets, and this is especially true if there aren’t many stop signs along a residential corridor, where drivers can easily pick up speed.

Traffic circles do three things in particular that are helpful in calming traffic:

1) They create a literal/physical interruption in the street so that people can’t blast through an intersection.

Here’s a photo of a permanent traffic circle in Dunbar Spring Neighborhood in Tucson, complete with public art developed by a local artist. While a person driving sure could try to plow over it, it’s unlikely to happen. Instead, they have to slow down and go around if they want to proceed straight.

2) Because they require people driving to “keep right” as they proceed—even when making a left-hand turn—they greatly reduce (and even eliminate) turning conflicts/crashes.

The graphic to the right shows how many points of potential conflict there are in a basic two-lane street (one lane in each direction) at a normal intersection vs. one with a traffic circle. As you can see, the fewer the points of conflict, the less likely a crash.

Image source: NextSTL.com

3) They also narrow down the intersection so that turns can’t be wide and sweeping, which means people driving have to slow way down to make left-hand turns.

The rendering to the right includes a neighborhood traffic circle, showing a slimmed-down intersection with tighter turn radii. This is much safer for everyone using the space, but especially people on foot.

Image source: NACTO

Unfortunately, permanent traffic circles aren’t the cheapest or easiest thing to install. They often require excavation (digging up of asphalt) which comes with all sorts of red tape, and the concrete curb needed comes with a cost, both in materials and in labor.

Quick-build traffic circles, on the other hand, are a handy way to reap the benefits of a traffic circle without a hefty price tag attached. Instead of removing asphalt, it simply gets painted with colorful murals that can be designed and informed by the surrounding community. Rather than permanent concrete curb, a combination of industrial-strength planters and flex posts can create the visual and physical barrier needed to protect the space and enforce the same driver behavior as permanent materials.

A completed quick-build traffic circle at the intersection of 8th Avenue and 25th Street, adjacent Ochoa Community School (Photo credit: Creatista)

Quick-build traffic circles require professional services (engineering, striping, etc.) to establish the footprint of the circle and install the signage and hardware to make it compliant with traffic safety standards, but the rest can be done entirely by neighbors and volunteers, leading to an end result that is both functional and joyful.

Curb extensions (a.k.a bulb-outs)

A lot of Tucson was developed during an era that prioritized the movement of individual cars, which meant wide streets, even in neighborhoods. Today, many of those streets are over-built (they’re bigger than they need to be for the volume of car traffic they carry) or they no longer match the types of movement that are taking place regularly, like biking and walking. This is where curb extensions (a.k.a bulb-outs, and sometimes also referred to as “chicanes”) come in.

Curb extensions can look different in residential vs. commercial settings, but generally their primary function is to “choke down” parts of a street. They effectively narrow the travel lanes so that people driving have to slow down in order to maneuver. This is typically done either at the approaches to an intersection (the corners of an intersection) or by staggering bulb-outs down a block, alternating sides.

Here in Tucson, permanent bulb-outs are often paired with rainwater harvesting strategies and native plants to create cool, green micro-climates for passersby.

Example of a permanent bulb-out in Rincon Heights neighborhoods, combined with water harvesting features and native plants. This design extends the corner curb, shortening the crossing distance for people on foot or using mobility devices. (Image source: Watershed Management Group)

This photo shows a permanent mid-block bulb-out (also referred to as a “chicane”) being constructed to include water harvesting features. Notice the bulb-out across the street; together these two features slim-down the street, helping calm traffic passing through. (Image source: Watershed Management Group)

As you can see from the pictures above, permanent bulb-outs and curb extensions can be pretty resource intensive, requiring excavation, asphalt removal, setting concrete forms, pouring concrete, and more. The good news is that—like traffic circles—the same traffic calming impacts can be created through a quick-build approach if needed.

Here’s an example of a quick-build project completed in a more commercial area in Tucson in 2018, where traffic safety was a concern:

A quick-build curb extensions project at the intersection of 6th Avenue and 7th Street here in Tucson. (Photo credit: Taylor Miller)

One of the biggest advantages to bulb-outs is that they shorten crossing distances from one curb to the next, which is especially important in busy retail/urban settings with a lot of people moving about in different ways. Wide streets mean long crossing distances for people on foot and using mobility devices. The longer people are crossing an intersection, the more time they’re exposed to car traffic and at risk of being hit, so reducing that distance is key. Curb extensions are one way of narrowing down crossing distances, by extending the curb radius at either end.

Before the paint, planters, and flex posts created the bulb-outs at this intersection, people on foot had to cross multiple lanes of traffic as well as turn lanes, which added up to a substantial distance to traverse. You can see they now are only exposed in the area where the crosswalk hits the edge of each end of the bulb-out, which reduces their exposure time by at least a third if not more. That reduced exposure is important in an area like this, which used to be industrial, but is now full of shops and destinations that have generated a lot more foot traffic.

Another advantage to bulb-outs is that they create order; they give everyone using the intersection clear visual cues as to where to be and where to expect other people to be, whether biking, walking, rolling, or driving. In the case of quick-builds, the addition of colorful murals, planters, greenery, and flex posts help establish which spaces are for people outside of cars, and which spaces are for people inside of cars. This helps everyone navigate the intersection in a safer way.

Help establish bulb-outs in downtown this October

This month Living Streets Alliance will be partnering with Tucson Department of Transportation & Mobility and dozens of community partners to implement a quick-build in downtown. A street mural and planters will be installed on 6th Avenue between 12th and 13th streets with community volunteers to make this active area of Downtown safer for people traveling through the intersection or visiting Children’s Museum Tucson or Armory Park. You are encouraged to join us on October 22nd to transform the space, and help bring three quick-build bulb-outs to life!