So why do you think the Tullys haven’t built roads, bridges, or canals? Canals may be too capital intensive without support from King’s Landing but bridges and roads should be possible. Do you think it’s because the Riverlands have only been under local rule for 300 years?

There is some evidence of bridge-building – Fairmarket had a wooden bridge, for example – but the big thing that’s lacking is a bridge over the Trident where the Kingsroad crosses the river at the Ruby Ford. 

Part of it has to do with internal vs. external rule, but it’s also the case that the River Kings of old weren’t always keen on development in the outlying regions, and would deny city charters to places on the periphery that they feared might become breakaways if they got too powerful. 

So for the Tullys, for example, it may be that they didn’t build a bridge over the Ruby Ford because the Freys objected to another bridge, the Mootons argued that it would take trade away from Maidenpool, the Blackwoods demanded that the Tullys pay for a stone bridge at Fairmarket (which would probably make the Brackens oppose any bridge-building out of spite, and they probably insist that the money should be spent on roads instead, along with the other houses whose lands abut the River Road or the Kingsroad), and other houses might have objected to paying taxes to benefit House Roote alone. A powerful enough ruling House could cow this kind of opposition or buy them off by handing out other benefits (offices, honors, various land rights), but the Tullys aren’t as secure in their position.