A local blog called New Urban Roswell serves as a platform for blogger Mike Hadden to tout the various urban planning concepts he supports. Mike is a knowledgeable guy and often makes some good points as he did in this post entitled “Traffic Misconceptions”. The article does clear up some common misconceptions but unfortunately it also perpetuates one about mixed use housing.

The truth is that high density mixed use means high traffic… period. But when it comes to the fans of high density mixed use developments they all seem to display an “Imperviousness to evidence” as characterized by Mona Charen in this article at National Review online.

Here is what Mike wrote:

High Density Development Creates Traffic – This one is legitimate under the assumption that you pack people into condos and create a
dense SINGLE USE environment. Single use environments are a sure fire way to create traffic.

I know that mixed use fanatics want that statement to be true but that doesn’t make it so. Look at the actual numbers.

According to the traffic analysis submitted for the MetLife mixed use development in Alpharetta they will build 532 units of high density housing on approximately 8 acres of land. That is a lot of units for 8 acres but each condominium does create fewer vehicular trips than a single family home and they even get a 2% trip reduction factor for being in a mixed use development.

Now let’s compare that to the horrible old sprawl that urban planners abhor but the people in Alpharetta love to call home. To be generous we will say that “sprawl” would create a density of 4 units per acre. That number is awfully high if you are going to put in some of those loathsome cul de sacs but we’ll give the mixed use fanatics the benefit of the doubt. That means that 32 single family homes could be built on the same 8 acres of land that MetLife will use to cram in 532 units. That is 500 more families on 8 acres of land.

So how do 500 additional families reduce traffic? They don’t and the dirty little secret is that any urban planner worth their salt knows it. High density mixed use is just a way for developers to make more money and urban planners to achieve their other goals of mass transit and affordable housing.

Let’s look at the traffic numbers. MetLife submitted a traffic analysis that shows the 532 condos were expected to create about 3,000 additional trips from 8 acres of land. Single family homes usually cause about twice as many trips as condos so we could have expected about 180 trips if the property had been developed as a typical Alpharetta neighborhood. That means the MetLife condos added 2,820 more car trips than single family homes would have. That’s a 1466% increase in traffic!

There is an old saying that goes something like this, “Don’t pee on my head and tell me it’s raining”. Well just to be safe the next time a fan of a high density mixed use development tells you that it will reduce traffic I suggest you have an umbrella handy.