Non-Grid Cities: When Roads Shut Down

What happens to a non-grid metropolitan transportation network when a section of a major highway shuts down? Is traffic efficiently re-routed around the closed-down portion of the artery? Are cars merely delayed, or does ordinary travel suddenly take ten times as long?

I had the opportunity to find out last month. In Pittsburgh, a major portion of I-376 eastbound was closed for repairs. This is the road the runs away from downtown towards the eastern suburbs. If you want to see a rather good map of the closed portion, you can see it at this site. Anyway, the big problem is that since Pittsburgh is a non-grid city, detoured traffic can't simply cut up, over, and back down to get past a closed portion of a highway. Instead, detoured traffic has to wander around, up, and down myriad hills in 25mph residential neighborhoods. A trip that normally would take about 15 minutes (getting to I-76 from downtown) took around 2.5 hours. Yikes!

So, as much as I find non-grid cities interesting, this is a serious weakness!