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Minimizing Vehicle Makes Transport Infrastructure Sustainable

Updated: Feb 3

Transport infrastructure must be as least invasive to nature and people as possible. And rationalizing the new vehicles' requirements gets along with making the infrastructure more sustainable. The estimates below run for an active personal vehicle FELA of minimally functional size, SUV or ordinary car, and semi-truck.

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 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 the structure (dead weight). Our assumptions hold because most bridge or highway spans support a few lanes of vehicles crawling bumper-to-bumper in gridlocks (the worst load case).

Computation for the effective beam depth of 0.6 m (height of bearing cross section) and concrete compressive strength of 35 MPa 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 sedans to light trucks) with an average weight of 60kN, an effective length of 8m (design length plus "bumper-to-bumper" gap in slow traffic), and heavy semi-trucks of 360kN, of 30m length give 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 road lane designed only for FELA needs 1200N/5 = 240N/m of concrete, for carrying 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, Canada). They live and work in the 100x100m blocks 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 of the environmental cost of construction of the city transport infrastructure. For a city that doesn't allow cars except for semi-trucks on its roads, this emission is 7x (4MtCO2), and for the most 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 population size, so it's not the numbers irrelevant to urbanism on Earth.

Ok, it is evident with the new cities that are smart enough to live without cars. What about existing infrastructure?

Resurfacing a mile-lane in a city is ~$1200. The axle's load determines the fatigue damage on any road structure and its pavements. Since the 1960s, the 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 20x the capital costs, even after adjusting for inflation.

FELA axial load is about 1kN, whereas for our average car, it is 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. Given that all other factors are the same (proper drainage in areas of likely frosts), FELA wheels won't damage existing roads if car traffic detours from this stretch.

According to a report published by the Urban Institute, the annual expenditure on roads in the U.S. was $181B in 2017, with roughly three-quarters of the budget from state and local government and a quarter from federal funding. When divided by the population, the amount was about $560 per capita. For our city's population of a million 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 of 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 everyone is a commuter. As such, you can cut global GHGE by more than 20% if you've chosen to replace your car with FELA.

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