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I'm honestly really skeptical of the cost effectiveness of pedestrian tunnels as a form of transportation. Asking Claude for estimates on tunnel construction costs gets me the following:
A 1-mile pedestrian tunnel would likely cost $15M-$30M for basic construction ($3,000-$6,000 per foot based on utility tunnel costs), plus 30% for ventilation, lighting, and safety systems ($4.5M-$9M), and ongoing maintenance of ~$500K/year.
To put this in perspective: Converting Portland's 400 miles of bike lanes to tunnels would cost $7.8B-$15.6B upfront (1.1-2.3× Portland's entire annual budget) plus $200M/year in maintenance. For that same $15.6B, you could:
Even for a modest 5-mile grid serving 10,000 daily users (optimistic for suburbs), that's $10K-$20K per user in construction costs alone.
Alternative: A comprehensive street-level mural program might cost $100K-$200K per mile, achieving similar visual variety at ~1% of the tunnel cost.
You're probably right. I neglected check how effective this would be in any quantitative sense.
I think you underestimate the cost of street-level murals ($100K / mi is about $60 / m), and neglect the benefit of tunnels' inevitable insulation, but the decision would probably end up the same.
If you're going to do something that huge, why not put the cars underground? I suppose it would be more expensive, but adding any extensive tunnel system at all to an existing built up area seems likely to be prohibitively expensive, tremendously disruptive. and, at least until the other two are fixed, politically impossible. So why not go for the more attractive impossibility?
Moving thru a visually-varied environment helps you remember what you think, say, and hear. Adding visual variety to an area thus aids the memories of those passing thru it, and, on average, makes it look nicer. Dense cities, especially those with mixed-use zoning, already have many mutually-distinct buildings. Some other small areas, like parks, are similarly intricate. Suburbs and blander cities, however, are mostly dull arrays of streets and houses. We can do better.
Visual art can be almost arbitrarily detailed and unique. If we cover walls around streets with visual art, the problem is solved. However, most walls around streets are the outer walls of buildings, most of which are privately owned, only some of which would approve of adding lots of art. Putting art on the street-ground itself helps, but people moving outside look to the sides more than down (citation needed), and getting walked on, cycled on, and driven over could wear away the paint (or equivalent).
In much of the US, urban and (even more so) suburban streets are, regrettably, dominated by automobiles. Ideally, we would use automobiles a lot less. But, for a probably-effective stopgap: invite walking and cycling in an underground network of tunnels. Artificial underground space can get dreary, but a tunnel necessarily has walls, all of which could be delightfully coated with a wild assortment of images, completely solving my current concern. Tunnels would also be thermally insulated from the above world, and so have more stable, pleasant temperatures — especially important when moving without enclosed vehicles.
Much as it may be putting pedals before handlebars to design them in such detail:
Good art — at least, good-enough-art — could come from graffiti, if legalised with the right caveats, like
Enforcing elaborate rules on graffiti is harder and more expensive than prohibiting graffiti is harder and more expensive than allowing all graffiti. It may end up easier and cheaper to prohibit all graffiti and publicly fund visual art for tunnels.