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Comment by hjnilsson | Hacker News Reader

A very important aspect to consider here is that a roman road did not have 100 000+ multi-ton vehicles traveling on them per day. The reason roman roads lasted long is that the load on a road with only manual labor traffic is a thousand times less than that of a modern highway.

Old roads in Europe that are subject to truck and car traffic crumble very quickly unless meticulously maintained.

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And even then, most road degradation is due to heavy trucks. Cars contribute very little.

http://facweb.knowlton.ohio-state.edu/pviton/courses2/crp776...

Skip to page 4, where it covers ESAL. A standard trailer is expected to do around 800-1000 times the damage of a standard passenger car. The conclusion:

"When discussing road wear cars don't matter: road damage is effectively caused by trucks."

> road damage is effectively caused by trucks.

So, if road use is charged by a steeply progressive schedule, and driver cost is not an issue, will we see fleets of light autonomous trucks replace the heavyweights?

No, because the weight is the cargo. As more and more semi-truck trailer beds transition to aluminum floor joists, for weight reduction, it's an overall increase in productivity because the truck can now haul more cargo weight.

TBF, I suspect GP is referring to reducing the gross weight of trucks (vehicle + load), rather than the net of the vehicle alone.

That's possible too, but would be tremendously less efficient as you'd have the same air resistence (or at least a substantial amount) but without the same cargo capacity.

Railroads tend not to develop potholes.

You can't really reduce the net weight whilst carrying gross weight beyond a point because the structure won't cope with holding the cargo. Maybe you can optimise some of it out but whether a human presses pedals/turns wheels or a computer does is relatively immaterial towards the net weight of the vehicle structure. Autonomy won't play a big role in that compared with improved design and materials.

Also, remember that roads aren't made out of head-hardened solid steel - if they were, they'd probably nearly forever.

Rail itself may not get quickly damaged (though they do) however rail wheels, which are made of relatively softer metal, develop all kinds of damage, require the machining away of the damaged surface periodically (as in, wheels shrink over time as mateiral is cut off it to get to new metal below) and only last a matter of years for heavy haul environments: http://www.asa.transport.nsw.gov.au/sites/default/files/asa/...

Search for spalling, shelling and rolling contact fatigue as examples.

It would be fuel vs. road cost ...

(There might be a paper in figuring out the sweet spot given hypothetical costs ...)

However, road damage doesn't scale with the weight. The damage roughly scales like the weight per axle to the power four! e.g. http://www.pavementinteractive.org/equivalent-single-axle-lo...

I figured it would be a power, was just hand-waving with "steeply progressive" ;-)

Most Roman cargo moved on ships. Roads were for unavoidable overland transport, where rivers didn't suffice, and largely involved personal transport or local movements.

Though the Romans didn't make heavy use of them, one of the first major inland cargo transport systems was canal networks. Canals are almost the equivalent of railroads (trading speed for bandwidth), and have the useful property, I realised a while back, of not requiring roadbed maintenance or resurfacing. Canals don't develop potholes, get muddy, or suffer from the carriage of heavy loads.

The canal boom in Europe began proper in the 1500s, though there were some earlier instances.

Canals can silt up requiring dredging.

Yes, but that's not affected by use or vessel weight.

It is. Bigger vessels means more banks erosion. This is an issue now, this may not have been one at a time of animal traction or river barges.

At what speeds?

Perhaps I wasn't explicit enough in the post, but yes I realize this. The point I was trying to make is that whatever the reason (including the purpose of the infrastructure, its usage patterns, its requirements), if a project could satisfy its purpose with fewer resources/less GDP needing to be reinvested over time, then this represents a higher relative return on their investment. GDP, having the dimension of time, wouldn't necessarily reflect their overall wealth, including the uncounted utility from historical investments.

The upfront investment of a Roman road might still be comparable to the lifetime investment of a modern one when you factor the human resource. How many man hours are spent on a mile of road, including building the tools (cement truck, bulldozer, etc) now versus the mass manual labor required then.

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