With the Trump wall coming up for discussion on a fairly regular basis and with Donald Trump's rather fluid estimates of the cost of the wall, a brief by Konstantin Kakaes in the MIT Technology Review breaks down the numbers for us. For the purposes of the brief, the author assumes a wall length of 1000 miles with natural barriers such as mountains blocking cross-border traffic in some regions and the existing border fencing providing security for the remainder of the 1989 mile-long international border.
First, here is a map showing the proposed route of the wall:
Here is map showing the existing portion of the border barrier system:
There is already 653 miles of existing fencing along the border which has cost $2.3 billion in construction costs since 2006 with the first fence being constructed back in 1990; some of this "wall" looks like these photos:
About half of the 653 miles of existing fencing is designed to stop vehicular traffic with most of the rest designed to stop foot traffic. In total, there are 48 controlled U.S. - Mexico border crossings with 330 ports of entry. As you can see from the photo above, much of the fence would provide very little impediment for an immigrant.
If a concrete wall were to be built as Donald Trump has suggested, it would be constructed using concrete reinforced with steel rebar; the author suggests that a wall between 35 and 65 feet in height would be required, recommending an average height of 50 feet with a foundation that extends 15 feet underground for both stability and to deter cross-border tunnelling with a one foot thickness to reduce the risk of boring through the wall. To put this into perspective, the relatively short sections of existing concrete wall that separates Israel from Palestine is up to 26 feet in height and looks like this:
A wall of the dimensions proposed by the author would use 12.7 million cubic metres of structural concrete (average cost $900 per cubic metre) and 2.3 billion kilograms of rebar (average cost $2 per kilogram). In addition, there would be labor costs for construction which are likely to be high given the ruggedness and remoteness of some of the terrain, however, for the sake of this estimation, the author uses the same labor costs as what went into building the border fences between 2006 and 2009 as noted above.
Here is a cost summary for 1000 miles of concrete wall:
Concrete - $8.73 billion
Rebar - $4.6 billion
Labor - $2.3 billion
TOTAL - $15.63 billion
According to the author, the total cost of megascale projects in the United States is generally two to three times the material costs. In this case, the material costs total $13.33 billion; this results in total costs ranging between $26.7 billion and $39.9 billion. And, as we know, governments rarely spend less than projected on major construction projects. It is also important to remember that much of the existing barrier is an easily breached fence meaning that well more than 1000 miles may be required to ensure security.
In this era of a $20 trillion debt, America's taxpayers will have to decide whether the added security is worth the cost.