The Silent Killer of Sustainable Design
A beautifully cut piece of natural granite requires very little manufacturing energy compared to concrete, but if that granite is quarried overseas, loaded onto a diesel cargo ship, transferred to a freight train, and finally trucked hundreds of miles to a job site, the emissions from moving it can far exceed the emissions of locally poured concrete. This is transport emissions, the silent killer of sustainable design, and because landscape materials like stone, soil, gravel, and timber are incredibly heavy and voluminous, moving them burns real fossil fuel that has to be managed strictly through supply chain logistics.
Ton-Miles and the Three Transport Modes
Transport emissions are calculated using ton-miles, the carbon cost of moving one ton of material over one mile, with the mode of transportation dictating the severity of the emissions. Ocean freight is highly efficient per ton-mile, but the sheer distance of international shipping adds up to massive total carbon loads regardless. Rail freight is the most carbon-efficient method for moving heavy bulk materials like gravel or timber over long domestic distances. Heavy-duty trucking is the most carbon-intensive transport method of all, and trucking crushed stone 500 miles can produce a diesel carbon footprint that exceeds the footprint of the stone itself.
The Five-Hundred-Mile Radius Rule
To guarantee low transport emissions and secure sustainability points such as LEED’s materials credits, heavy material specification should generally stay within a 500-mile radius of the job site. This forces designers to embrace the local vernacular, using regional limestone instead of imported travertine, and local nursery stock instead of trucking trees across the continent.
Relative Carbon Intensity by Transport Mode
Heavy diesel trucking carries the highest relative intensity, around 160 grams of CO2 per ton-mile, best limited to final-mile delivery with aggregates sourced locally wherever possible. Diesel freight train carries a considerably lower intensity, around 20 grams, ideal for long-distance domestic timber or steel transport. Ocean cargo ship carries the lowest per-mile intensity of all, around 10 grams, efficient per mile but easily negated by the thousands of miles overseas shipping typically covers, which is why heavy hardscape materials sourced from overseas should generally be avoided.
Where the Calculation Work Goes
Tracking the weight of every specified material, determining exact mileage from quarry to site, and applying correct emission factors for different vehicle types requires complex logistical accounting. CalcType’s Embodied Carbon Calculators take material weights, transport methods, and travel distances and instantly calculate the total logistical carbon footprint of a project.