Introducing Place-Making Innovative Intersections
By Michael R. Brown, PE, AICP
• Traffic Engineer, New Urbanism Fan, and
Founder of Metro Analytics
Drive Slower, Travel Faster
What if you could reduce speed limits, narrow
lanes, or even eliminate a lane, and still give drivers
faster average speeds? A wide array of new
opportunities for Complete Streets and Economic
Development would emerge.
Communities want to reinvigorate their ugly, highspeed “stroads” as more “Complete Streets” with
room for bikes, pedestrians, transit, and
landscaping. But such stroads often have extreme
congestion and the public worries that such visions
will make a bad situation worse, so Place-making
desires often end with no political path forward.
But such wishful thinking is impossible, isn’t it? If
not, surely the world would have discovered the
magic by now? Well, decades ago engineers
invented many intersection designs that can handle
more cars with the same number of lanes. Sounds
like an auto-oriented solution, right? And that’s how
most engineers have approached it. But some
designs have amazing Livability features, and need
not be “auto-oriented” if approached correctly.
Thus traffic engineers usually get their way. But
now there are win-win strategies that can improve
walkability, while at the same time accommodating
the same or even greater numbers of vehicles with
less congestion.
What’s the magic? It’s what we call “Place-Making
Innovative Intersection” designs. If any of these are
good fits for your situation, there’s a good chance
you can shake hands with engineers rather than
wrestle for the upper-hand.
Turns out left-arrows introduce a lot of inefficiency
and even safety hazards at signals, so the
common-thread of all innovative intersections is to
eliminate these left-turn phases. There are more
than a dozen designs in the family. Some are
irredeemably auto-oriented, such as the Continuous
Flow Intersection. But the family also includes
potential “Place-Makers” such as Quadrant
Intersections, Town Center Intersections, and ThruTurn Intersections for high-volume settings. Also
Roundabouts for mid-volume settings. Metro
Analytics specializes in planning and multi-criteria
evaluation of these.
But before reviewing their place-making potential,
the next section shows some of the math behind
how more auto-capacity per lane can potentially be
used to improve livability – the math that can help
you negotiate with engineers.
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doesn’t always need to be for cars. In this chart,
suppose you have an arterial with 3-lanes each
direction where each lane can carry 700 vehicles
per hour per lane (blue), or 2,100 total. Many want
to convert the 3rd lane to transit, but the 800-lb
gorilla (engineers, and majority in autos who back
them), say it can’t be done without harming traffic
flow. But if innovative intersections can help the
remaining two lanes each carry 1,100, then the
result is 2,200 for autos (about the same as before),
plus transit, and a much higher overall “peoplecapacity.”
Drive Slower, Travel Faster: The Math
Traffic engineers tend to define their purpose in life
around helping autos get from A to B as fast as
possible. When a road gets congested, they default
to widening it, inducing even more demand. Now
they’ve got new arrows in their quiver – innovative
intersections. So before these new tools become
auto-oriented, we can leverage the benefits to autos
to create more livable, multi-modal boulevards.
A typical suburban intersection with left-turn arrows
will get congested at fairly low volumes. You might
wait more than 5-minutes, inching forward watching
the signal turn red/green several times before you
even reach the front of the line. Innovative
intersection designs can often get the average wait
at these signals down below one-minute.
So which is faster? Racing at 50 mph on a “stroad”
only to wait 3-5 minutes at signals? Or a 35 mph
boulevard where you wait just a minute or less at
intersections? Engineers probably want both the
intersection improvements and the higher speed
limit, but may admit that today’s situation would still
be faster for drivers even if speed limits are
reduced. So use intersection gains as a bargaining
chip for reducing the speed limit and narrowing
lanes to 10 or 11 feet. That’s driving slower, but
traveling faster – win-win for autos, bike/ped, and
economic development.
And if you can’t quite steal a lane, you probably can
steal “parts of lanes.” Engineers always want 12-ft
lanes, their standard for stroads signed at 45-mph
and higher. But if efficient intersections reduce
delay, then you can reduce speeds to 35 without
hindering average speeds. That’s where a new 10ft standard kicks in – the best-practice width
supported by both ITE and
CNU.
How to Steal a Traffic Lane
Innovative Intersections boost lane efficiency. A
typical suburban arterial might carry about 700
vehicles per hour per lane. But if revamped to
include innovative intersections, the boost might
jump to 1100 vehicles or more.
Check out StreetPlan.net,
Metro’s free Complete
Street cross-section design
tool that follows these
ITE/CNU guidelines.
So how is accommodating more cars with the same
lanes transit friendly? The increased capacity
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Retrofitting Suburban Intersections as “Place-Makers”
Ideally, urban intersections would be small and carry
modest volumes of traffic. That is possible in
environments with high connectivity and good local
grids. But suburbs tend to lack connectivity, and thus
the few thru-streets become overwhelmed with traffic,
degrading adjacent land-uses quickly. Many believe
Complete Street retrofits would allow land uses to
rebound, but it is daunting to create walkable, livable
boulevards and at the same time accommodate high
volumes of traffic that isn’t going away.
Quadrants, Thru-Turns, and Town Center
Intersections are three design styles that can bridge
the chasm, helping manage high traffic at lower
maximum speeds without harming average speeds.
Quadrants
The Quadrant and Continuous Flow Intersection
designs have a lot in common. The top diagram
shows the basic pattern of a CFI, which is increasingly
popular with traffic engineers. If you haven’t seen it
yet, you will. Left-turning traffic waits at a mid-block
location, and then crosses over oncoming traffic
during the east-west phase. When north-south turns
green (shown in yellow), the red lefts can proceed at
the same time as yellow.
The CFI is good at congestion-relief, but it is harmful
for would-be mixed-use environments. Bike,
pedestrian, and transit access is very intimidating.
Businesses suffer from restricted access. Even if fixed
guideway transit can be accommodated, the CFI will
impede transit-oriented economic development.
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Quadrants are very similar to a CFI, in that traffic waits
in a mid-block left pocket just like at a CFI, but instead
of crossing over the oncoming lane and in front of
development, it crosses behind development with a
“backage road.” What would that do for walkability
and development? First, the main intersection can be
much tighter than other designs, with far fewer
pedestrian conflicts.
impeding traffic. Such mid-blocks are also good for
pedestrians, who simply cannot cross legally or safely
without additional signals.
How they work
A Quadrant is extremely versatile. It can be operated
as a “mini-cloverleaf,” where 3-rights make a left. Or it
can be operated similar to a CFI, where people use a
mid-block intersection, but instead go behind existing
development.
The bottom sketch shows that previous left-turn
pockets are no longer needed at the main intersection,
so the space is available for other uses such as
landscape, pedestrian refuge or fixed-guideway
transit. Next, vehicles access parking from the backside, which allows the elimination of driveways on the
main streets, replaced by shared-wall buildings. The
design also expands the local grid, creating additional
circulatory options, and creating high visibility from
additional parcels to catalyze a “town center” or
business district rather than just “an intersection.”
Preserving the Option for Quadrants
At any intersection that is likely to someday have a lot
of traffic, consider creating “backage roads.” In the
short term, there is no need to route left-turn traffic on
these – just use regular left-turn arrows if that’s what’s
politically possible. They’ll still provide better
connectivity and opportunities for a larger Activity
Center rather than a focus on a single intersection.
And in the long run they are “get out of jail free” cards
to be invoked at any time to reroute lefts, reducing
congestion and freeing up former turn pockets in
support of a stronger Activity Center.
Quadrants may require mid-block signals for handling
left turns. These mid-block signals can be
synchronized with the main intersection to avoid
Advantages of Quadrants
Impressive vehicle-capacity gains
Center-transit, pedestrian refuge, etc.
Safer for both autos and pedestrians
Short signal cycles
Expands activity center grid connectivity
Enhances / Catalyzes Economic Development
Adds value to many more parcels
Low cost (if backage roads already exist)
Political salve to obtain transit lanes
Easy front-door/back-door access to retail
Compatible with traditional signals
Disadvantages
Initial confusion for drivers
Potential out of direction travel
May add signals to corridor
May be hard to create back-side streets
May affect some parcels negatively
Resistance if back-way is single-family
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lack wide medians, but often do have deep
setbacks and under-utilized parking where these
ellipses / bulb-outs / roundabouts could be
created without excessive impacts.
Thru-Turns
Have you ever tried to turn left from a parking lot
onto a busy arterial, and found it so impossible to
get a gap in both directions that you instead went
right, then made a U-turn? A Thru-Turn simply
formalizes this action.
Ellipses / roundabouts create interior space
which can be used as a transit station or gateway
landscaping helping define a “Place.” They also
help calm traffic before it enters a pedestrianoriented space.
In these diagrams, some lefts are completed as
“Right-U-Thru.” Others are “Thru-U-Right.”
Bowties, Loons, Median-U’s, Superstreets, and
even roundabouts can generally be included as
part of the Thru-Turn family.
Without lefts, the main intersection has fewer
conflicts, making it safer for pedestrians. With no
need for left turn pockets, former pockets can be
pedestrian refuge, transit, and other uses.
This concept is also known as a “Michigan Left.”
Decades ago, Michigan required a number of
state highways to have very wide medians so
that these U-Turns could occur. Other states
Rerouting lefts along 10-15 mph roundabouts in
a retail center
Imagine a 7-lane arterial crossing another 7-lane arterial, with double-left turn pockets on each
approach. Pedestrian Purgatory! This Bowtie design can replace that, improving walkability and
livability. The ellipses redirect left turns as “right-U-thru” or “thru-U-right,” and also serve to
calm traffic. Space inside the ellipse can be used for landscaping, a transit station, and to define
the edges of a key “Place” in the community. Former left-turn pockets become pedestrian refuge.
Yes, these will still be major highways with a lot of traffic, but speed limits in this area can now be
reduced without reducing average traffic speeds, and reinvestment in mixed-use development can
start to occur.
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This was Utah’s first 3-leg Thru-Turn,
opened in 2011. It eliminated congestion,
but was done “on the cheap,” lacking
pedestrian refuge, landscaped ellipses,
lower speed limits, and other walkability
features. Community reception was
mixed. They liked reduced congestion,
but hated confusing paths and the ugly
result. Lesson: If your first thru-turn
doesn’t invest in place-making, you may
not get to build another one!
Advantages of Thru-Turns & Bowties
Impressive vehicle-capacity gains
Shorter signal cycles
Safer for both autos and pedestrians
Enhances and motivates TOD
Often very low cost
Politically easier to obtain transit lanes
Can enhance retail frontage
Planted medians, access control, circulation.
Compatible with traditional signals
Former lefts reclaimed for center-running
transit, pedestrian refuge, etc.
Disadvantages
Initial confusion for drivers
Out of direction travel for lefts
Space required for bulb-outs / ellipses
Educational effort to win over skeptics
Still high volume – doesn’t make cars go away
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auto-oriented intersection, accompanied by
excessive congestion. This diagram by
Calthorpe Associates shows how the two
highways can each be divided into lower-speed
one-way streets as they cross, resulting in four
smaller, friendlier intersections, with more parcels
having good access and visibility. The system of
four intersections can handle more overall traffic
than the double-left intersection it replaces, but
importantly it feels like less traffic, because each
intersection is small and in fact has less traffic.
Town Center
Intersections
A Town Center Intersection is created any time
one-way streets are involved. Though one-ways
are not particularly “innovative,” they qualify as
innovative because there is no need for left-turn
arrows, since there is no opposing traffic.
Imagine two typical suburban “stroad” highways
coming together. Normally it would result in
double-left turn pockets and a single massive
This Town Center Intersection in San Marcos, CA shows how a system of four simple intersections
replaces a single huge one (16 popular corner parcels, as opposed to just 4). Even though this
system can handle very high traffic, photo shows that it does so within an attractive and safer
pedestrian context.
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One-Ways Not Inherently High Speed
But One-Ways are Bad, Aren’t They?
It is currently in vogue to convert one-ways back to
two-way, under the pretention that one-ways are “highspeed, auto-oriented” and therefore bad for multimodal Place-Making. No doubt there are situations
where conversion makes good sense, but I believe
one-ways are unfairly taking the blame for autooriented situations.
Regarding the last point, couplets encourage highspeeds only if intentionally or inadvertently designed
for high speeds. The speed of traffic has nothing to do
with whether it is one-way or two-way. Wide lanes,
on-street parking, signal spacing, speed limits, and the
nature of the urban fabric have much more influence
on speed.
Why do one-ways have a bad rep? Many one-way
streets were introduced in the 1950’s and 60’s as
traffic engineers wrestled with how to deliver huge
numbers of vehicles into these centers using streets
that had always been very narrow. In that generation,
Complete Streets and traffic calming were far from
anyone’s mind, so one-way couplets were designed
for high speeds. Land uses and other modes were an
afterthought at best.
Yes, one-way streets with closely spaced signals can
achieve perfect signal progression. While that may
sound “fast and auto-oriented” because green-lights
are good for autos, it actually means we can more
easily achieve compliance with any desired speed
limit. For example, with two-way streets, if the speed
limit is 35, most people will drive 40-45 mph. But
because signals can be set to fall like dominoes on a
one-way street, a limit of 35 results in vehicle speeds
of exactly 35, as the public quickly discerns there is no
advantage in exceeding 35 mph. Thus couplets can
be set for low-speed or high-speed progression,
without affecting overall capacity much.
Thus because there are many examples of older,
high-speed, auto-oriented couplets, it is common for
planners and the general public to unfairly malign
couplets as incompatible with walkable, sustainable
design.
Two-Way Conversion Helped Business!
With many one-way to two-way conversions, it is
common to hear that business has improved, along
with more walking and biking, and renewed
development interest. But such conversions often
include significant Complete Street beautification
efforts, speed reductions, etc., so it is a mistake to
conclude that one-way vs. two-way was the change of
greatest significance.
Walkable Facts About One-Ways
1. Pavement is half as wide; thus easier to cross
2. Signal cycles are shorter; thus faster to cross
3. Pedestrians only need gaps in one direction; thus
faster and safer if crossing without a signal.
4. Traffic is spread across two streets, doubling the
parcels with high visibility and good access.
5. Narrow streets have better pedestrian enclosure
even when buildings are only one or two stories.
6. One-ways do not require a left-turn lane, which
means more space for other uses.
7. Speed is independent of capacity – you can move
just as many vehicles at 30 mph as at 50 mph.
Redesign high-speed one-ways as low-speed,
walkable boulevards without creating congestion.
One-Ways Support Activity Centers
Auto-accessibility may not sound like a critical need for
Transit-Oriented Development, but it is. Would-be
activity centers can never reach critical mass for major
transit investments until first growing as dense as
auto-access can allow.
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One-way streets are a common thread in many of
America’s largest and most successful urban centers.
Portland, Denver, Manhattan, New Orleans, and even
Boise, Idaho are among many examples, and all have
many examples of walkable, low-speed yet high traffic
couplets.
plaza. Denver’s 16th Street Mall and Boulder’s Pearl
Street are good examples of triplets.
With as popular as alternative modes are in these
places, their ecosystems still require vehicle circulation
for deliveries, construction, transit, and a great many
private and shared autos. Their network of one-way
streets ensures that no particular street has
overwhelming traffic.
Try converting their one-ways back to two-way, and
the immediate effect would be excessive congestion,
which would decrease Livability and decrease market
interest in continued development. If your goal is to
support an ever-expanding activity center, why stunt
its potential with inefficient two-way streets that are
inherently less safe and higher anxiety for pedestrians
than similar-speed one-ways?
Retrofits vs. Greenfield Opportunities
Obviously creating a couplet requires a second street
– challenging to retrofit if there is no second street, or
if the candidate alignment has politically challenging
existing uses. There are often more opportunities
than meet the eye, and Metro Analytics is skilled at
finding them. (And thus my impassioned plea to
strongly reconsider abandoning existing one-ways).
In this Greenfield concept, a major arterial entering the
activity center (black) is split to two one-way streams,
and slowed to 30 mph. A center alignment (blue) is
for light-rail and other pedestrian-oriented uses. It
crosses several other smaller couplets, as well as
many two-way streets.
But there are huge swaths of Greenfield areas being
planned as major activity centers, or have potential to
evolve as centers, where couplets could work well.
One drawback of a couplet is that for transit, people
prefer to come back to the same place they got off.
Thus in Greenfield environments, consider creating a
“Triplet” such as in the figure below. As traffic
approaches a sensitive place, it is diverted to the outer
edges. But transit can continue on to a pedestrian
On the next page, city leadership in Logan, Utah is
excited to convert their asphalt-dominated historic
Main Street into a one-way couplet, partly to handle
growth in traffic, but also to gain space for protected
bike lanes, better streetscape, and possibly angleparking in some sections – all within the same 126’.
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If vehicles can keep moving, even with designs
assuring low speeds, then huge numbers of vehicles
can move through sensitive areas without it ever
feeling like huge numbers.
Give Town-Center Intersections a Try
In summary, there is nothing inherently “auto-oriented”
about one-way streets. Yes, they are more efficient at
moving more vehicles with less delay, but that creates
opportunities to reclaim automobile space.
Where two highways cross in rapidly urbanizing
Greenfield areas, consider adopting Calthorpe’s Town
Center design, or Metro’s Triplet design, before
random development paints you into a box and dooms
you to a future where traffic engineers intervene to
force double-left intersections or worse.
If “efficient vehicles” seems auto-oriented, consider
that high delay also feels auto-oriented, because
delayed vehicles stacked up for blocks are annoying
to everyone and pressures engineers to go rouge.
Advantages of Couplets
Impressive vehicle capacity gains
Less pavement = Complete Street space
Shorter signal cycles
Safer for autos and pedestrians
Enhances and motivates TOD
Little additional cost if planned from start
Expands grid, enabling larger activity center
If synchronized, low speed limits observed
Narrow streets help pedestrian enclosure
Proven: common feature of thriving Centers
Disadvantages
Initial confusion for drivers
Out of direction travel (offset by less delay)
Opposition if 2nd street has incompatible uses
Convenience stores may have some loss.
Transit board stop different than exit stop
Risk of high-speed if designed poorly
Change affects many people (education effort)
Unwarranted stigma to overcome.
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