The Diverging Diamond Interchange: good for cars, but what about pedestrians?

About a year ago, shortly before I left Provo for Philadelphia, there was a big stir in the news about a revolutionary interchange being designed in American Fork, Utah. Horrocks Engineering was designing a diverging diamond interchange (DDI), only the third in the nation, to try to improve traffic flow over I-15.

From http://www.deseretnews.com/article/705337066/I-15-bridge-set-for-installation.html

What is revolutionary about this design is that it minimizes left turns, which slow down traffic both for the turners and those whose lanes they are turning across, by having all traffic cross onto the left side of the road for a short time. Although this may sound confusing, you can see how the various movements would work here.

I sort of forgot about this for the next year, until I read today’s article in Slate by Tom Vanderbilt. In it, Vanderbilt discusses this and other methods (such as the much-maligned Jersey Jug Handle) that have been tried to improve left-turn related highway problems. The DDI has gone through various tests (although there is not currently a standardized design) and drivers are able to overcome the strange feeling of driving on the left fairly quickly (although it should be noted that the DDI does depend on traffic islands to make sure that drivers don’t just continue going straight on into incoming traffic).

There are a number of issues related to the DDI and questions that, in its infancy, have yet to be answered. Vanderbilt begins addressing what I think it the most important issue, that of pedestrian access. “While the intersections are avowedly built with access for pedestrians and cyclists in mind, as this rather involved walk-through video of a DDI reveals, it doesn’t really feel like a human-scaled environment,” he says. The FHA argues that it is safer for pedestrians because they only have to cross traffic going one way each time they cross. While this is true, pedestrians have to cross four signals to get to the other side of the road, giving them plenty of opportunity to be hit by cars and also forcing them to wait in inhospitable environments at each crossing. On the plus side though, by breaking the lanes up into smaller segments, it makes it easier to jaywalk across (an inevitability that few planners or engineers consider).

There are two basic systems of pedestrian access in a DDI, as are detailed in this selection from the ACEC of Michigan’s report on DDIs:

From http://www.acecmi.org/pdf/DDI.pdf.

In addition to those specified above, another disadvantage of the center crossing is the feeling of being surrounded by cars on either side. This can be mitigated with the high walls that are seen in the video above, but that just exchanges being surrounded by cars with a feeling of claustrophobia.

A number of sources say that the safety problems of crossing so many lanes of traffic can be addressed through signalization. However, doing so would interrupt the continuous traffic flow that is the main advantage of the DDI for motorists. You might as well do a traditional diamond.

You might be able to tell, but despite the professional assurances from highwaymen, I am skeptical about the advantages of the DDI for pedestrians. But I really want to know what you think. Is the DDI any better or worse for pedestrians than a traditional freeway interchange, and why?

Vanderbilt ends his post with a great point. He mentions that the assumptions about DDIs and their traffic improvements are based on the idea that traffic will continue to increase because we will continue suburban sprawl patterns of development that make it hard to be a pedestrian. The question is, if we continue to neglect the link between land use and transportation, and refuse to build balanced transportation systems, “Can you ever truly design your way out of congestion?”

Carla Saulter’s Urban Family Values

I came across Carla Saulter’s first article on Grist way back in November.  Since then, I’ve been real busy, but taking all that time has given Carla enough time to write a lot more really great articles, which I have just gotten caught up on this week.  I felt that the best way for me to address Carla’s articles was to do one big long post instead of a number of short ones, so here is my assessment of four articles from Saulter’s Urban Family Values column.  This column is updated bi-weekly, so keep checking it out.

Why public transportation is good for kids

In her first post, Saulter explains that her family, with two small kids, doesn’t own a car, and does so on purpose.  When she and her husband first found themselves expecting, their friends informed them that they would have to get a car.  They did not follow that advice, and while Saulter has found that there are challenges to living without a car with children, it isn’t because transit is necessarily bad for children, but because most American cities have been designed or redesigned for cars.  She argues that there are a number of reasons that living car-free is good for children’s health and well-being.  First of all, car culture discourages exercise.  “[T]he auto-centric built environment in many communities makes walking and cycling unpleasant, impractical, and quite often, dangerous,” she says.  At the same time, cars add to air pollution, not only outdoors but also inside the cooped up interior of the car.  Car crashes also cause more deaths among American children than anything else.  Buses, on the other hand, are the safest form of road travel.

While cars are in many ways dangerous for kids, transit has many positive aspects.  Transit almost always requires some walking, and those who use transit are more likely to meet the CDC’s daily exercise requirements.  Taking transit frees parents from the requirements of driving and allows them to actually concentrate on and interact with their children.  For many kids, the mere experience of riding transit can be like a game.  Transit kids also gain the skills necessary for transit ridership (packing, trip planning, stop recognition, schedule reading) well before their car-dependent peers are able to drive, making them more responsible and more independent.  They also learn how to interact with strangers appropriately, unlike kids who spend their time in cars with only family members.

Moving to the suburbs for your kids?  Think again

Saulter points out the irony that many want a better world for our children, when many of the things we do to keep them “safe” in the here and now are damaging their future.  While many parents think large, green lawns in the suburbs are good for their kids, the car-dependent, resource-intensive lifestyle of the suburbs is bad for kids (as illustrated in the last article) and bad for the planet.  Instead, Saulter’s version of “family friendly” is characterized as “dense, diverse, and transit-rich.”  Denser neighborhoods include smaller homes, which require fewer resources to heat and cool, as well as less land.  They also limit the amount of things we buy, due to limited space, which also limits our waste.  Neighbors share more, whether it be public parks, third places like cafes, public facilities like libraries, or large-scale entertainment such as movie theaters replacing staying at home and watching TV.  Infrastructure can also be delivered more efficiently in denser areas.

Denser areas also allow for more transportation options, making transit, walking and cycling viable alternatives to car transportation.  Dense neighborhoods also provide many of the benefits listed under public transit in the last article, including learning how to work with strangers, sensory stimulation, and independent problem solving.  Cities also have more cultural amenities and encourage fitness and community.

Driving a car doesn’t mean being in control

Car-dependent people often ask car-free people how they can get to places in a hurry, when transit isn’t a timely option.  While transit is almost always timely for me personally, and while the options of cabs, car sharing and ambulances provide many other options, Saulter argues, “what they’re really asking is, how do I deal with the lack of control associated with not having a car?”  The thing is, cars don’t always provide the most freedom and convenience.  For instance, I can get to City Hall faster via transit than I can in a car, without having to worry about traffic.  Also, the weather, particularly in winter, can effectively disable cars, while trains and subways keep running.  In the suburbs, when you’re snowed in, you don’t have any options, while a foot of snow at my house in Philadelphia doesn’t keep me from walking the one block to 7-11 to get milk.

Car drivers also lack financial freedom: if you’re dependent on your car, then you’re stuck with buying gas no matter how expensive it is.  Meanwhile, Holly and I discussed over Christmas break how we never pay attention to gas prices anymore because it doesn’t cost anything to walk.  Holly and I also could walk to three hospitals in less time than my parents in the suburbs could drive to one.  Even if one of us were injured, ambulances or even cabs could get us there in no time.  In Saulter’s words, “My family doesn’t have a car, but what we do have is access, and that makes me feel far more in control than a car ever could.”

Want a safe place to raise kids?  Look to the cities

The reason many parents choose to live in the suburbs is because of crime and other safety concerns.  The truth is, cities are much more safe than they are made to appear.  Saulter looks to Lenore Skenazy, the woman who let her nine-year-old son ride the New York subway alone, wrote about it in The New York Sun, and was later labeled in many news sources as “the worst mom in America.”  In response, she wrote a book called Free Range Kids and started a blog, both of which discuss how parents need to get over their entrenched fears and look at the facts.  Despite news coverage of the worst aspects of cities, as well as TV shows that lead people to believe that people are dying left and right in major cities, the truth of the matter is that the chances of a child being abducted and killed are one in 1.5 million.

In reality, a child has a much higher chance of dying of a car crash in the suburbs than being murdered in the city.  The most dangerous areas overall in the nine metro areas covered in a University of Virginia study were the outer suburbs.  Children are much more likely to be killed in car crashes than to be murdered by a stranger (which is actually less likely than them being murdered by someone they know), and the car-dependent suburbs make them more dangerous than the city with its strangers.  In fact, all crime, including assaults and other violent crime, are at record lows across the country.  And while some crimes, especially gang-related, are higher in cities, there are also many aspects that make cities safer, such as many more people with many more eyes on the street.  One important thing is to teach kids basic street smarts.  One important thing is that they shouldn’t go anywhere with people they don’t know, but they should be taught to talk to strangers so that they can ask them for help.

Carla Saulter’s articles, so far, are full of wonderful advice for urban families and address some of the incorrect ideas held about where it is right for one to raise a family.  I hope that her writing changes some minds, and I look forward to following her work.

A Week of Biking Joyously

This article was posted on Planetizen by Jay Walljasper, author of The Great Neighborhood Book: A Do-It-Yourself Guide to Placemaking, which I have just started reading and am very much enjoying so far.  In the article, Walljasper describes a recent trip to the Netherlands and what he learned about biking there.  The Dutch do have a few advantages relative to the US when it comes to biking (flat land and a long tradition of doing so), but for the most part people there own cars like we do, they just don’t choose to use them whenever they go out.  The Dutch also have a habit of combining transit trips with bike trips, something that many American systems (Philadelphia’s in particular) are not very well suited to.

One thing that they found that set the Netherlands apart by a long shot was that 95% of kids ages 10-12 ride their bike to school, compared to only 15% in the US.  Dutch kids have bike safety classes, almost like driver’s ed, from a young age.  And at age 11, the kids can take a biking safety course and get a certificate of completion, like a sort of non-binding driver’s license that gets hung on the wall by proud parents.  Not only do the classes help the kids become better bikers, it also helps them be more aware of cyclists even if they choose to drive in the future.

Another issue is safety.  60% of Americans said that they would be more willing to bike if they felt safer doing so.  In the Hague, city officials have worked to make separate, colored bike paths, and where that isn’t possible, create “bike boulevards” where bikes have priority over motorized traffic.  But people aren’t just worried about their safety while riding; they want to make sure that their bike can be safely parked and locked when they get to their destination.  And not only that, but many residences don’t have a safe place to park the bike, and many cyclists feel obligated to take their bikes indoors for their safety.  Officials in the Hague are also working on secure bike parking in residences and commercial locations, some of them attended by staff like at a car parking garage.  Bike racks and sheds are becoming available in some high-density neighborhoods, sometimes using one car parking space to fit ten bikes.

A great example of a bike-centric development in the Netherlands is Amsterdam’s Java Island.

from http://nl.wikipedia.org/wiki/Java-eiland

The development is bike, pedestrian, transit and even boat friendly, and still has room for cars, but they are relegated to a very few roads and underground parking garages while other modes have free reign of the parks, bridges and docks all around the island without having to deal with cars.  The Dutch call this type of development “Auto Luw,” which translates to “car light” or “car sparse.”  These developments are now the official policy of the city of Amsterdam.

I will finish this post with a most hopeful video from filmmaker Michael W. Bauch.  He and his family exchanged houses with a family in Amsterdam, and when they came back to the States, they couldn’t give up the bikes.  Enjoy.