The Stroad-Taming Power of Quadrant Intersections

Mike Brown is a transportation engineer and Strong Towns member. Today he shares a guest post proposing one way to tame dangerous stroads.

In the quest to tame stroads, we often make our case to stakeholders with pictures like this one, which I created using StreetPlan.net. 

Everyone loves your design!  Everyone except the city’s engineer and accountant.  A typical engineer might have at least five concerns, which can kill your vision if you don’t address them.  I’m an engineer, so let me help you see what engineers see, and don’t see.

First, they don’t see that modest investments in walkability can attract development back to languishing corridors, saving money via #NoNewRoads at the fringe.  They don’t see that the stroad is likely a net liability while the people-oriented street — when factoring in higher tax collections from development along it — is likely a net positive.  They don’t see well that the forgiveness of slow speeds is safer than forgiving design at high speeds. 

Here’s what they think they see, which they’ll explain to the Mayor in private:

  1. Narrower lanes? College taught me that anything less than 12 feet is sub-standard.  10-11 ft might be ok if only drivers would slow down, but that will take excessive enforcement.  This isn’t a walkable area anyway, and we’ll just anger voters if we make their drive take longer. 
  2. How do you turn left?  Sure, the pedestrian realm is great, and there is a fantastic planted median with pedestrian refuge.  But this landscape apparently comes by eliminating left turns!  That would cause rebellion among drivers, who are 90% of your voters!  We must accommodate left-turns, and we must keep congestion at tolerable levels.
  3. On-Street Parking?  Side friction from parking will reduce vehicle capacity.  This is a busy corridor with few alternative routes.  Can we afford to lose capacity for on-street parking when there is plenty of off-street parking?
  4. Reduced Speed Limit?  The lower speed limit is safer for pedestrians, but there are virtually no pedestrians!  It's an enforcement problem and it will just make it take longer for the 90% to get around, so I wouldn’t recommend it.
  5. Where’s the money for this?  We’re way behind on filling potholes.  How are we supposed to raise money to construct all these amenities? 

So that’s it in a nutshell. Many engineers see their Hippocratic Oath as “first do no harm to the 90%” and they define “harm” as anything that threatens to make auto trips take longer. 

From Win-Lose to Win-Win

As an engineer, I’m sympathetic to these arguments.  Most of us travel by car a fair amount, and who wants any trip to take longer? Thus many engineers see proposals like the one above as Win-Lose; most people (drivers) lose so a few (pedestrians) can win.

It’s important to find Win-Win answers or you may never out-wrestle engineers who are proficient at pointing out how stroad-taming ideas will make drive trips take longer for suburbia’s 90%’ers. 

Quadrant intersections are a tool that can help engineers and planners shake hands, but you’ve probably never even heard of them.  Today, I want to explain how stroad intersections are a problem for all modes — including vehicles — and how Quadrant intersections can reduce vehicle delay (the part engineers care about most).  Then I’ll show how to leverage what engineers care about to convert stroads into safer streets.

Quadrant design

Left-Turns: A Problem, and an Opportunity

Stroad intersections almost always have dedicated left-turn arrows with single or double-left lanes.  Without arrows, people turning left would never get a chance to move safely given the endless stream of oncoming cars.  But these arrows require a lot of “cycle time,” which creates delay.

With a Quadrant, left turns are prohibited at the main intersection and, instead, are routed behind development using less critical nearby intersections.  That creates more green time at the main intersection and less delay overall, which means drivers can get to where they’re going all the faster.  How is faster good?  Stay with me, but first let’s look at the placemaking opportunities created by Quadrants.

Quadrants & Place-Making

When left turns are routed behind development, vacated left lanes can become trees, pedestrian refuge, a center-running transit stop, or wider sidewalks.  The required backway allows parking access from behind, which makes it easier to eliminate driveways and encourage traditional Main Street development, where adjacent buildings touch each other and abut the sidewalk.  

The backway also has new visibility, which activates more property along that path and increases connectivity. There are far fewer pedestrian conflicts at the main intersection and there are new, safe pedestrian crossings at other intersections.  All of this helps the space become a true activity center as opposed to just an intersection with four popular corners.  Now let’s focus on how helping drivers travel faster can be a good thing for walkability. 

Drive Slower… Travel Faster!

In the typical #SlowTheCars debate, you'd have a tough time getting most engineers to agree to a 5 mph speed reduction  (let alone 15, which is what many stroads need) because they think it will harm the interests of the majority. 

But since Quadrants usually reduce overall delay for drivers, engineers can see in their own software how it’s possible to reduce the maximum speed, and still increase the average speed.    

Here’s an example: To go a half-mile, the faster you drive, the fewer seconds it takes... until you factor in traffic signals. With Quadrants, you’re stuck for less time, so you might still end up getting through faster, even if the speed limit is 15 mph slower.  That’s why increasing the average drive speed (or at least not reducing it) is good for walkability — because it helps engineers, drivers, and politicians get on-board with walkability!

Revisiting our Cross-Section

Since the Quadrant design reduces delay, what can that mean for the five things engineers were concerned about?

  1. Narrow Lanes: By reducing delay, narrowing lanes to reduce maximum speeds will not reduce the overall average speed.  Check!
  2. Left Turns: With lefts routed to secondary intersections, the previous double-lefts can be converted to other uses through the core of the activity center.  Check!
  3. On-Street Parking:  Parking always reduces lane efficiency, but the higher efficiency of the Quadrant could offset the losses caused by parking.  This doesn’t mean engineers will agree with on-street parking for every case, but it increases the odds.  Quadrants also increase the odds of reducing the number of lanes without measurably increasing traffic delays.  Check!
  4. Reduced Speed Limit:  Since Quadrants allow you to reduce maximum speed without affecting average speed, it becomes easier to justify the traffic-calming features that will reduce maximum speeds, without need for aggressive enforcement.  Check!
  5. Paying for it: Safe streets add value to adjacent real estate. Catalyzing infill otherwise bound for further out also reduces health costs and duplicate infrastructure costs, which are arguments to use with candidate funding agencies.  So, ought there be a way to pay for this? Check!

Why not a Road Diet?

You might look at my street illustration at the top and say, “It’s nicer than the stroad, but it still has two lanes each direction, so isn’t it just lipstick on a pig?”  It’s true, the safest, most economically productive streets often have just one lane in each direction.  However, this article is about retrofitting stroads.  Because stroads were designed with a “hierarchy of flow” (find and link to Chuck’s article about hierarchy) and exist in places with terrible connectivity, traffic may have few other options.  Quadrants do increase the odds of reducing the number of lanes, but you may still need to accommodate high traffic volumes due to poor connectivity. 

A Worthy Tool for a Strong Towns Toolbox

In conclusion, a Quadrant may benefit your city for several reasons:

  • Makes it possible to drive slower, but travel faster, to gain critical allies.
  • Former left turn pockets available for other uses. 
  • Increases localized grid connectivity, and creates safer, shorter pedestrian crossings.
  • Back-access parking facilitates shared-wall “Main Street” buildings.
  • Backways activate more infill, which reduces duplicate infrastructure
  • Converts stroad from fiscally net negative to net positive.
  • Thousands of stroad locations where this design may be easily achievable.

Learn more about Quadrants and other Place-Making Innovative Intersections at InnovativeIntersections.org, and watch this fun YouTube Video of how slower can be faster.

All graphics created by Mike Brown.

ABOUT THE AUTHOR

Mike Brown is a New Urbanist transportation engineer with new strategies to convert stroads into walkable boulevards.  He hopes to stop the “build-our-way-out with freeways” temptation by taming freeways instead, or downsizing those that just don’t make sense to continue.  Mike founded Metro Analytics to pursue those objectives.  Metro sponsors InnovativeIntersections.org, where you can discover cutting-edge Place-Making methods for managing high-volumes of traffic at low speeds, and at the same time catalyze mixed-use development.  Metro also sponsors StreetPlan.net, a free Complete Street cross-section development tool that follows ITE/CNU best practice guidelines.  Mike is based in Salt Lake City, Utah. 

Mike Brown