Summary of "Placemaking Alternative Intersection" research underway for the North Carolina Department of Transportation.
What is the problem our research aims to solve?
In a word... Stroads.
The North Carolina Department of Transportation frequently hears from communities across the state expressing a desire to catalyze walkable mixed-use development along large, auto-oriented, decaying suburban commercial highways. Such highways are increasingly referred to as “Stroads” – a street/road hybrid. Stroads have the economic activity of a historic “Norman Rockwell Main Street.” They also have fast speed limits akin to the rural roads they often once were (45 mph+). Sadly, once fully suburbanized, Stroads have neither the charm of great streets, nor the speed of great roads anymore, due to congestion and frequent stop lights.
Unfortunately, even with plenty of funding, it is almost impossible to convert a Stroad into a “Complete Street” that has impressive street trees, bike paths, transit, on-street parking, and pedestrian-oriented features that can catalyze walkable development.
An "Anywhere USA Stroad" vs a Stroad that was successfully converted to a "Complete Street" (Lancaster Blvd, Lancaster, CA)
Why is it nearly impossible to convert Stroads into Complete Streets?
Traffic: Many Stroads do and always will carry huge amounts of traffic – a challenging fact for creating a walkable environment.
Traffic Engineers: Engineers worry that efforts to slow traffic to speeds safe enough for pedestrians may also exacerbate delay and congestion. There is still a high value on drive time, even if there is also increasing desire for slower livability. If they don't get behind your vision, you'll probably lose!
Lack of Know How: Even when engineers are on-board with traffic calming, very few know what to do - their toolbox is limited. With so many cars, driveways, business signs, etc., finding room for street trees, on-street parking, and improving alternative modes may be extremely difficult. They end up putting "lipstick on the pig" because it's the best they can figure out.
Thus, the main problem to solve is to discover innovative ways to manage high volumes of traffic, to the satisfaction of engineers, and at the same time create a truly transformative environment that can catalyze impressive scales of walkable development.
How suburban value is created, then lost, and how we hope to create it again.
The diagram below shows how Stroads often start as rural roads, then explode into popular "Shiny Stroads," and finally collapse into "Ugly Stroads" in economic reversal. After collapse, many communities hope to reignite their popularity as "Complete Streets," but neither engineers, nor urban architects, nor planners know how to do much more than "lipstick on the pig." Our research aims to empower these groups to truly transform Stroads into Complete Streets that can catalyze walkable mixed-use development.
Phase 1: Rural Road: Fast and Safe, Low Development
Phase 2: Shiny Stroad: Development causes DOT to widen, but they also attempt to keep speed limits high. Auto-oriented commercial overwhelms the system with lots of complex stop lights.
Phase 3: Ugly Stroad: As the shiny wears off, businesses and residents of means flee to the next "New and Shiny Stroad." DOTs and communities are left without tax revenue to maintain both the old and new Stroad. But traffic engineers are happy - speeds have improved now that there's less congestion since half the people fled!
Phase 4: Reclaim as Complete Street? This is very hard to achieve, and that is the point of our research! We think we have some new strategies that can be effective.
The Core of several“Big Ideas” for solving this problem
NCDOT hired NC State University and Urban Innovators to research new strategies for making progress toward managing the high traffic volumes found on Stroads in more pedestrian-friendly ways. The research team believes that redesigning how major intersections operate is key to accomplishing this goal. There are three innovate “Alternative Intersection” types that the team believes have strong potential for managing high volumes of traffic, and at the same time catalyzing walkable development: “Quadrant Intersections, U-Turn Intersections, and One-Way Split Intersections.” Each of these is described briefly here, followed by examples of how these could be implemented in the Greenville study area.
First, what is a “Stroad Intersection”?
Two-way Stroads almost always have 2-3 through lanes in each direction. At an intersection with another Stroad, engineers install left-turn arrows, and often "double lefts," so lefts can be accomplished safely. The case above has 9-lanes a pedestrian must cross - roughly 150 feet, or half a football field! Extremely intimidating, and virtually guarantees that this area can NEVER be truly walkable and livable without a significant reinvention. Traffic almost always drives 45 mph or faster between stop lights, even if the speed limit is 35 mph. But the actual average speed is far slower than 35 mph due so much delay at the stop lights!
Below shows how left-turn arrows create a four-phase signal, which in turn limits how much green time is available for the major through movements. This NCDOT research is demonstrating that Quadrant, U-Turn, and One-Way Intersections can reduce the number of signal phases. This makes it possible to drive slower (think tortoise through a walkable environment), but also travel the same average speed if not faster due to more green time.
What is a Quadrant Intersection?
Instead of managing lefts directly at the main intersection, a Quadrant redirects those movements along a back-way path as shown here. Notice that vehicles on the red path have no out-of-direction travel. Those following the blue path have some out-of-direction, but even they are likely to get to where they’re going quicker due to less congestion. Former left-turn lanes can now be converted into planted medians with trees and pedestrian refuge areas in the middle of cross-walks. The Quadrant backway improves access and visibility for parcels along that backway, adding value to that land and making it attractive for mixed-use development. There are many variations of this idea, such as a four-quadrant system that converts blue paths into red paths, but this diagram is a good start.
What is a U-Turn Intersection?
There is a huge amount of variation in the U-Turn family of designs, but the basic idea is to convert lefts into “Thru + U + Right.” In the "Before" diagram, the purple cars require a left-turn arrow – a four-phase signal that creates congestion and requires extra lanes for storing left-turning cars. In the "After," lefts are now “Thru+U+Right.” Before, the blue and yellow cars are also in a predicament. Yellow needs a safe gap in BOTH directions (very hard to get), before it can enter. Blue needs a safe gap in only one direction, but this is still dangerous. The roundabouts make this easier, faster, and safer. Notice that like the Quadrant, the old left turn lanes can now be planted with trees, and you can have pedestrian refuge areas in the crosswalk.
What is a One-Way Split Intersection?
This can be a little harder to explain quickly, but the basic idea is that rather than having a single huge intersection, it is better for both livability and traffic management to split it into four one-way streets, creating four small intersections, then come back together on the other side. Below is such a situation near San Diego, and you can see how small and easily crossable these tiny intersections are for pedestrians. This idea is sometimes called a “Square-about” because it works a little like a roundabout, but in a larger “square” pattern. One-way streets usually come in pairs that are often called “One-way Couplets.”
Note: The reason this is highly efficient (meaning lots of green time for the tortoise) is because left turns on one-way streets do not need a left turn arrow, since there is no oncoming traffic. Our research shows that even though this environment has small, pedestrian-friendly intersections, the overall system can handle up to 80% more traffic than had it been a single huge 4-phase intersection.
The fact that it can handle more traffic means it is easier to support more development. For example, say you have today’s auto-oriented environment where 90% of traffic comes by car. If you triple the density and improve transit, walking, and biking, maybe you’ll get to 75% traffic by car. That’s pretty good! But 75% x triple the density = 2.25, or more than twice as many cars as before. That is a PROBLEM if the road can’t handle more cars. Luckily, this design CAN handle more.
Note: If it is impossible to create one-way couplets in both directions (i.e., both NS and EW with four intersections), you still get much of the benefit by creating a couplet in just one direction, resulting in two intersections. In other words, two Complete Street one-ways are better for traffic and livability than a single huge two-way Stroad, and four Complete Street one-ways are better than two.
Caution: Both Greenville and Smithfield agreed to be "Guinea pigs" for our ideas, with a caveat that none of the ideas have yet been, and may never be, vetted within a formal planning process. These are NOT recommendations for what each city should do, (though they eventually could be after a formal public involvement process). They are basically "free ideas," compliments of NCDOT and our research team, that each city is welcome to investigate further or reject. For research purposes, these are simply real-world models to learn from. This way NCDOT and other communities can determine if they'd like to pursue designs like this.
What are our ideas for Greenville?
The next graphics show how we applied some of these ideas near Greenville Mall on Greenville Blvd, Arlington Blvd, and Red Banks Road. At the right is the majority of the study area we selected, along with the Quadrant, U-Turn, and One-Way Couplet opportunities we have been exploring.
Note: The one-ways require two new streets, labeled "New SW" and "New NW". Both traverse mostly parking lots, but likely would hit the "blue buildings." The biggest hit is the southwest portion of the mall. This would only be implemented in conjunction with the mall owners - when of their own accord they decide they need to reinvent their property and want to explore this as an option.
One-Way Cross-Sections Near Mall
Below is how Greenville Blvd might change from a two-way Stroad into a one-way Complete Street. Notice that private parking between existing buildings and the right-of-way is a factor that inhibits walkability. The new design inverts private parking into public, allowing sidewalks to be pushed to the far outer edge. The overall amount of parking is similar, but it is also much more efficient (i.e., likely to be used), when it is in the public realm.
3D Before / After Renderings, One-Way Area
The series of sliders below show Before / After for the crossing one-way couplet concept in Greenville.
Concepts in Greenville: Quadrants at Arlington and Evans
The series of sliders below show Before / After for the four Quadrant intersection at Arlington Blvd and Evans Street.
Concepts in Greenville: U-Turn / Quad Combo
Below is a combination U-Turn+Quadrant. This would offer pedestrian refuge that the current design does not. This would make it a lot easier to reduce lane widths and create the ambiance that is necessary for mixed-use areas to take root. The chicanes introduced by what we call "teardrops" (non-roundabout U-turns), have a natural traffic calming effect.
Can this funky stuff fit in with New Urbanism? We think so, but we worry that too many Urbanists may see things through a "Back to the Future" lens - going back to Pre-WWII grids as our model for what is best going forward. That may be fine in Greenfield areas, but isn't helpful in suburbs without grids! This may be a way to fix what is broken - the "future" part of "Back to the Future," where we take crappy Stroads, tweak them with some weird stuff like this, then watch as they grow impressive walkable development that could never have happened without the weird stuff.
I think of these U-turns and Quadrants a little like a stent in an artery. If we compare suburbs to the obesity epidemic, suburbs never should have "eaten" (developed) in a way that ruins their health. Now that they're in a terrible place and facing heart attacks, these ideas may be like stents and stomach stapling, followed up with healthier living. Not as good as healthy living from the beginning, but a new lease on life - a way to get from bad to better.
Below are graphics from our Greenville, NC work, which are part of what we'll try to advance through this NSF grant.
Engineers install "raised medians" to force right-in / right-out, for safety, but this makes it hard to get back to where you came from. Frequent U-turns make it safe and easy, which in turn makes it easy to reclaim two-way turn lanes, or "suicide lanes," for street trees and more walkable uses.
Concepts in Smithfield: Crossing One-Ways
Consider the slider graphic below. Light blue segments are two-way Stroads today, and the red and orange represent opportunities where one-way couplets could be created with only minor impacts to existing development. In today's Stroad environment, Market Street currently has 4-lanes East-West through its historic downtown. It connects to I-95 on the east and is a rare crossing of Neuse River on the west. This means that as the city grows, there will be more traffic. It will be very hard to justify a “Road Diet” from 4 to 3-lanes. Instead, NCDOT will face pressure to remove on-street parking and have a 5 or 6-lane cross-section within the 78-ft ROW. Brightleaf is already a 5-lane Stroad. With traffic sure to grow, it will be very hard to manage the present system. Even if NCDOT widens these - makes them even bigger Stroads - they will not work very well for traffic, and any placemaking actions will amount to "lipstick on a pig".
These one-way couplets would create capacity for the future and reduce today’s congestion considerably. But "more traffic capacity" need not equate to less walkable. In fact we think the one-ways create a bridge to walkability that is impossible to get otherwise. The graphics below tell the story of how it is possible to create capacity for the future, and at the same time catalyze walkable development.
Both Greenville and Smithfield have a nearly an identical opportunity for replacing two 5-lane Stroads with four much friendlier one-ways. In the Greenville case, new one-way alignments must be developed through parking lots and by removing a significant building at the mall. In this Smithfield case, the needed parallel streets are already there, and would just need upgrading.
The graphics below focus on this area. Both Greenville and Smithfield have a nearly identical opportunity for replacing two 5-lane Stroads with four much friendlier one-ways. In the Greenville case, new one-way alignments must be developed through parking lots and by removing a significant building at the mall. In this Smithfield case, the needed parallel streets are already there, and would just need upgrading.
Concepts in Smithfield: Crossing One-Ways
Brightleaf and Market Street
Below is a slider showing today's 4-lane, 78-ft cross section. It has a lot of nice "Street" elements: many historic buildings adjacent to sidewalks, some street trees, on-street parking, and very narrow traffic lanes. But it is also incapable of supporting much traffic due to shared thru-right, thru-left, and side friction with parking. A "road diet" with just one lane each direction and a two-way left-turn lane would help walkability and might even help a little with today's traffic, but it cannot accommodate growing traffic associated with the fact that this street connects with a freeway interchange AND a rare river crossing. Something will give, and that something is almost always a "bigger stroad," - in this case a likely loss of on-street parking ad a minimum.
The one-way cross section shows how you can get a better pedestrian environment, with a "slow lane" of about 10-15 mph for bikes and vehicles turning left or accessing parking. It handles more traffic, creates a wider pedestrian "furniture zone," accommodates bikes and transit, has safer parking, and encourages mixed-use development not only here, but also on a similar eastbound street. Given that all things must be compared NOT to the ideal, but to the likely alternative, what is not to love about this?
Below is today vs what NCDOT may be likely to do as traffic continues to grow. Notice today's single left lanes become double lefts. Today's shared thru+right becomes a dedicated right. A few of the auto oriented buildings on the bottom and left give way to "slightly larger" auto-oriented buildings.
Below compares the NCDOT "double left" default (from above), to how it could be if some directions of flow are relocated to other corridors. The much more human-scale streets easily have room for premium street trees, "slow lanes" for bikes and other low-speed vehicles, and impressive on-street reverse angle parking. Combine this infrastructure with form-based zoning codes to allow mixed uses up to 3-5 stories, and developers will salivate to construct "missing middle" projects not only here, but in the nearby areas also.
Below is the same angle, but zoomed out to see what we envisioned for the rest of the area, along with all four one-way intersections. Peach colored buildings are new, while white/brown and white/cream buildings are existing.
This is a good view of the pedestrian environment made possible by these one-ways.