Right now, the city has been systematically and incrementally tearing up segments of sidewalks throughout downtown and replacing the concrete with a dark, burgundy-ish brick. It's a nice brick aesthetically though I wonder what the albedo rating is (I'll get some surface temps taken soon). However, it does nothing to change the actual physical function of the street and therefore, there is little return on investment. As we know from the study of systems, cosmetic changes have the smallest impact compared to degree of intervention.
However, when cosmetic changes are in concert with or responsive to underlying changes, then there is some defensible merit. Integration begets Accommodation begets Decoration. Demand drives supply. This is the way cities and economic development work. As opposed to decoration which has the least bang for the buck, integration of networks has the most. Little interventions can create profound and transformative changes. Such is the way of emergence.
On the flipside, disintegrate networks the result is disinvestment. It is either a vicious or virtuous circle of self-reinforcing feedback loops generating ever more or less complex system (city). But at the core, it is integration of networks that creates for the most profound change.
When it comes to the question of how to improve our downtown streets and the (hypothetical) two solutions are either brick the sidewalks or add street trees to our rather shadeless, barren streetscapes, there are two primary factors to consider: 1) cost of implementation, and 2) return on investment (prettier is also a return on investment, but the only way to properly evaluate it is if it leads to increased pedestrian activity, meaning more foot traffic, more shops, more spending, therefore more real estate value, so yes, it all does come back to $ over the long-term).
The bricking of the sidewalks is a pet peave of mine because it is all cost and no functional change to the system. No increased integration, therefore no more accommodation (usable, leasable, valued space), ie no return on investment. It is merely cosmetic.
South side of Elm under construction (Before, so to speak):
And the north side of Elm, the finished "AFTER." Notice, no trees in either.
On the other hand, street trees do have a value on the other levels of the circle, however minimal, there exists an increment of improvement in terms of INTEGRATION, ACCOMMODATION, and DECORATION.
First, the DECORATIVE aspect is obvious. Trees are nice. Sometimes even, happy.
Second, is the ACCOMMODATIVE aspect. Trees provide shade. In hot climates, a decent amount of shade can mean 5, 10, or even 20 degrees difference in microclimatic temperatures. Most traditional/historic cities in hot climates don't have many street trees in their public streets because the buildings were built so close together to prevent heat gain from reaching the street. Roofs provided the majority of the surface area and in general were designed to reflect heat away, protecting the public realm below.
In many cases, Dallas has vast, wide, expansive public rights-of-way (see Elm street above). This is not because of having lots of land. It's economically inefficient to be so profligate with a resource. Instead, we have wide roads not for geographic nor economic reasons but arbitrary ones: traffic formulae so disconnected from the true purpose of cities or how they function and the predicate of the equation is invariably and predictably, anti-city.
Last, in terms of INTEGRATION, street trees provide a rhythm and buffer along streets, particularly wider, faster streets such as the arterials carving up downtown. The visual friction calms traffic, however slight, there is an effect. Slower traffic makes streets more comfortable and less dangerous for pedestrians. Shockingly, more pedestrians emerge.
Slower thru traffic means improved cross traffic and therefore a better, more integrative overall network even if that means a slowing of the segment from point A to B. It's points C, D, E, F, etc. that also matter. Furthermore, since slowed traffic means more pedestrians, it often means more overall traffic when factoring the various other forms of transportation (buses, bikes, pedestrians). For example, according to 2009 traffic data: Elm moves 13,000 cars per day (despite being five lanes wide). Neighboring Main Street move 9,000 per day despite being one lane each way. I'd also gander x2 for pedestrians. Likely greater overall traffic equaling greater value.
The irony therein, is that traffic engineers consider trees to be collision hazards. If a car hits them, that does damage to the car and potentially to the driver and passengers. They treat drivers as stupid. Drivers on the other hand, in the interest of self-preservation, perceive the danger of the various obstacles populating a street (other cars, trees, pedestrians, etc) and slow down. Even though there are more points of conflict on such streets, the severity of the accidents decreases dramatically.
On-street parking (another form of friction and pedestrian buffer) increases accidents 7% over streets w/o on-street parking. More wrecks. However, the severity, based on fatalities, drops 300%. Which is more important, your fender or your life? Fast moving cars or an economically and environmentally sustainable city that is a great place to live and do business? And we yield all hegemony to these people.
You'll notice I wrote more for each section (Int, Acc, Dec). That was only partially intentional, but also an inevitable outgrowth indicative of the complexity and potential to each. There is simply more to write about more powerful (yet less apparent) interventions.
Now for the Math:
Let's say 1 block = 300' in length
And the city wants to "improve" 20 300' segments of downtown.
Installing that brick, including demolition and everything, likely costs about $15 per square foot and each band of brick is about 5' wide.
That's 300' x 5' x 20 block segments x $15/ft = $450,000.
Since there is no systemic improvement there will be minimal, if any, return on that investment.
As for placing street trees instead of the brick in order to gain some degree of integration, accommodation, and decoration rather than mere decoration, the math goes:
Same 300' long block segments
Same 20 segments
Let's say we want to use larger, more mature 5" caliper trees for immediate impact and shade as opposed to the cheaper more commonly used 3 or 4" street trees.
That means spending about $1000 per tree which includes installation, irrigation, and material costs.
We can fit about 9 trees per segment.
That's 9 trees x 20 segments x $1000/tree = $180,000.
or 180 trees, 20 more comfortable, more pedestrian friendly streets for about 1/3rd of the price. And while it is fairly incalculable (one study in Portland shows $8,000 premium for individual houses on streets with street trees), I'm quite certain, it generates far more real estate value over the 20 blocks than the $180K. If we use that studies finding that each tree is worth $12,828 in increased real estate value, the 180 planted trees would represent an increase in downtown real estate values of $2.3 million on $180K initial investment, a return that pays for the bricks.
All of the above would be better than none of the above, but we're looking at an either/or scenario and leveraging one to get the other.
Proper urbanism is about generating bang for the buck. If it wasn't profitable, cities wouldn't persist nor exist for all of civilization. If it's merely buck and little to no bang, Ur Doing it Wrongz.