Updated: Jul 27, 2022
Transport Infrastructure must be the least invasive to nature and people as possible. And rationalizing the new vehicles' requirements gets along with making the infrastructure more sustainable.
The production of steel and cement, the main components of concrete, is one of the top three anthropogenic polluters. Roughly, a ton of concrete fabrication emits a ton of CO2 totaling 8% of the emission into the atmosphere - 3.5x the aviation industry.
Bridges and interchanges are mostly built of concrete, the amount of which depends on vehicle size. For our estimate, let’s consider a four-span continuous beam uniformly loaded by traffic (live weight) and by the structure itself (dead weight). Our assumptions hold because most spans support a few lanes of a few vehicles crawling bumper-to-bumper in gridlocks (the worst load case).
Computation for effective beam depth 0.6 m (height of bearing cross section) and concrete compressive strength of 35MPa, is plotted on the right.
Three cases for the live weights:
When a lane accommodates three FELAs in a row, of 3m effective length (with 0.6m gap in a gridlock), we get the live load from FELAs 1200N/m of span. That load accounts for three people per linear meter. The same reasoning for cars (any from sedan to light truck) of an average weight of 60kN, of an effective length of 8m, and heavy semi-trucks of 360kN, of 30m length gives us 7500N/m (including only 1-2 people on average) and 12000N/m accordingly.
When we build a car-free city where the average effective span of road structures is 20m, the computed live-to-dead weights ratio is 5 (see the plot). So, a lane of a road designed only for FELA needs 1200N/5 = 240N/m of concrete, to carry cars – 1500N/m, and for semi-trucks – 2400N/m. To account for pillars and fundaments we can increase this material intensity by 10% (although working differently, material for these elements is still proportional to the load) or 300N, 2000N, and 3000N per meter.
That means, car-free cities need 84-90% less steel and cement for transport infrastructure. To see how that looks in absolute CO2 emission for a town of a million populations, let the density be 4000 people per sq.km (Toronto), they live and work in 100x100m blocks that are served by four lanes of 100 +100 m of arterial roads per block (half of its perimeter). Under these assumptions for the car-free city, and considering a ton of CO2-intensity for concrete, we get 0.6MtCO2 is the environmental cost of construction of the city transport infrastructure. For a city that doesn’t allow semi-trucks on its roads, this emission is 7x (4MtCO2), and for the common case, it’s 10x (6MtCO2).
Building a thousand car-free cities would offset 0.5GtCO2 emission – the funding criterion. The top 80 megacities have this size of the population, so it’s not the numbers irrelevant to urbanism on Earth.
Ok, with the new cities that are smart enough to live without cars is clear. What about existing infrastructure?
Resurfacing a mile-lane in a city is ~$1200. The most critical factor of fatigue damage on any type of road structure and its pavements is the axle’s load. Since the 1960s, Generalized Fourth Power Law has been used to assess the relative damage to the pavement from a vehicle. Repairs to the concrete structures are estimated at roughly 20 x the capital costs, even after adjusting for inflation.
FELA axial load is about 1kN whereas for our average car it’s 30kN. Applying the Fourth Power Law we get that damage to the pavement from FELA traffic that carries 4-6 more people is 30^4 or a million times less. So given all other factors are the same (e.g. proper drainage in areas of likely frosts), existing roads won’t be damaged by FELA wheels and if car traffic is detoured from this stretch.
According to a report published by Urban Institute, the annual expenditure on roads in the U.S. was $181B in 2017, with roughly three-quarters of the budget coming from state and local government, and a quarter coming from federal funding. When divvied up by the population, the amount was about $560 per capita. For our city of a million population who decided to replace cars with FELA, savings from road maintenance is $560M per year. Concrete costs $200/cu.m, which amounts to 560/200=2.6M cu.m or 2.6*2.4t/cu.m = 6.24Mt of concrete not produced and the same amount CO2 not emitted by our smart city in a year. And again, we need only a thousand cities to become smart enough to save 0.5GtCO2e a year.
Building a thousand car-free cities for a billion urbanites will cut global GHGE by 0.5Gt and the same GHGE saving each year thanks to much easier maintenance of transport infrastructure.
Not everyone is a city planner or policymaker, but almost each of us is a commuter. As such, you can contribute to cutting global GHGE by more than 20% if you've chosen to replace your car with FELA.