Of course the Big Dig is more expensive, but you can't compare a single road to another road. If you take all roads in one area and divide it by the number of users you get a much more meaningful number.
Of course you are completely right that we need rural areas where we for example grow good or do other things that need lots of space. However, that doesn't happen in most suburbs. In fact suburbs typically keep their density artificially low for non other than vague aesthetic reasons. I myself live in the suburbs and find it very convenient. Would I do so if I had to pay for the street and sewer that lead to my house like my parents who live in Germany had to? Probably not. My parents had to pay about 20k, and that was because most of their property was on a main, federal road. Otherwise it would have been closer to 40. At the time I thought that was insane, but given that in a multi story apartment building the cost would have been much lower, it seems fair in hindsight.
In the US town where I live, which is admittedly more exurban/rural than suburban, I pay for my own septic system, trash, water, etc. Houses that were hooked up to sewer in another part of town a number of years back had to pay for that. No, in the US, you don't typically pay for public roads although people certainly pay for upkeep when they are on private roads as some are. (I'm off a state highway and have to handle the upkeep of my long private driveway.)
Personally, I'm no particular fan of traditional suburbs. But I'm also unconvinced that it's even desirable to especially encourage urban living--especially if, in practice, that means encouraging living in a few specific walkable cities. Presumably urban living in this context doesn't mean Las Vegas.
Of course you are completely right that we need rural areas where we for example grow good or do other things that need lots of space. However, that doesn't happen in most suburbs. In fact suburbs typically keep their density artificially low for non other than vague aesthetic reasons. I myself live in the suburbs and find it very convenient. Would I do so if I had to pay for the street and sewer that lead to my house like my parents who live in Germany had to? Probably not. My parents had to pay about 20k, and that was because most of their property was on a main, federal road. Otherwise it would have been closer to 40. At the time I thought that was insane, but given that in a multi story apartment building the cost would have been much lower, it seems fair in hindsight.