There are no stupid questions…
Dear NSQ,
I grew up in Pittsburgh and learned to drive there. Last month I took a left turn from Tate Street onto West Market Street the way I always have — when the light turned green, I went, before the oncoming traffic could reach the intersection. The driver across from me laid on the horn for what felt like a full second, and so did the two drivers behind him. Apparently in this town that maneuver is not a courtesy. It is a war crime.
Was my hometown crazy, or is the rest of the world?
— Left Behind in Greensboro
Neither. You’re describing the Pittsburgh Louie, sometimes called the Pittsburgh Left. The codified rule of the road is that oncoming through-traffic has the right of way over a vehicle making a left turn at a green light. The Louie says the left-turner goes first. In Pittsburgh, drivers wait for it, drivers behind the left-turner expect it, and drivers across from the left-turner permit it. Anyone who fails to participate gets honked at — including, apparently, oncoming drivers in Pittsburgh who treat the codified rule as if it were the operative one.
The interesting question is what the Louie was doing for you in Pittsburgh, and what was different about the same turn in Greensboro.
On a road with a dedicated left-turn lane and a left-turn arrow, the codified rule works fine. The left-turner pulls out of the through lane, waits in the turn lane, gets a brief priority window when the arrow goes green, and turns. Strip the turn lane out — and Pittsburgh’s topography means most intersections can’t fit one — and the rule starts failing. On a busy two-lane road under dense flow, the left-turner waits for a gap in oncoming traffic large enough to complete the turn, and as oncoming density rises, the probability of an adequate gap within a single green cycle drops below one. The left-turner waits across cycles. Expected wait grows without obvious bound.
And the wait isn’t only the left-turner’s. Without a turn lane, the would-be left-turner blocks the through lane behind them until they can complete the turn. Every car behind them waits the same wait — even though they only want to go straight. The codified rule’s failure mode on a two-lane road isn’t one driver’s inconvenience. It’s a queue of through-traffic forced to wait on a turn they’re not making.
The Louie clears both halves at once. It transfers priority, once per cycle, from the oncoming driver — who has plenty of green time and is going to keep moving — to the left-turner. The left-turner clears the intersection. The straight-going queue behind the left-turner clears with them. The oncoming driver loses two seconds. Almost everyone wins, and the biggest beneficiaries aren’t the drivers who learned the convention as left-turners. They’re the drivers behind the left-turner, who never had to learn it because they’re already going where they wanted to go.
Notice that this is also what a dedicated left-turn arrow does. The arrow doesn’t override the codified rule with some new principle; it implements the Louie in hardware — a brief window where oncoming traffic stops and the left-turner goes first. Pittsburgh, deprived of the geometry that makes the hardware feasible, evolved the convention instead. The arrow and the Louie are the same solution. One is legible to outsiders. The other isn’t.
The convention only works because everyone in Pittsburgh knows that everyone in Pittsburgh knows it. The oncoming driver expects the left-turner to go first; the left-turner expects the oncoming driver to expect it; the driver behind the left-turner expects the convention to hold and is annoyed when it doesn’t. This is what David Lewis called a convention: a regularity in behavior sustained because each party expects every other party to follow it, and they expect that, and they expect that, all the way up.
So why not just flip Pittsburgh? Sweden pulled this off in 1967 — Dagen H — switching from left-side to right-side driving on a single coordinated date, through months of pre-coordination and mass infrastructure replacement. The Pittsburgh equivalent would be a coordinated mass conversion: everyone wakes up tomorrow believing the codified rule is the operative one. Would Pittsburgh be better off? Arguably no — unless you also magically built turn lanes at every busy intersection. Sweden swapped the convention and repainted every road, because the old convention wasn’t substituting for any infrastructure the new one needed. The Louie is. Flip the common knowledge without flipping the geometry, and you’ve just installed the codified rule’s failure mode on every busy two-lane street in town.
What you took with you when you left Pittsburgh was the rule. What you couldn’t take was the common knowledge — or the constraint the common knowledge was answering. Greensboro has different roads, different turn lanes, different geometry. The codified rule there isn’t quite the same rule it was in Pittsburgh, in the sense that matters. The maneuver got honked at not because the maneuver changed but because you crossed a zip code line and the whole stack — rule, convention, the geometry the convention was quietly substituting for — wasn’t there anymore.
This is why I named the column the way I did. Your question sounds maximally stupid — did I just imagine the rules of the road were different in my hometown? — and the answer turns out to be that you didn’t imagine it at all. What was different was a context the Pennsylvania driver’s manual doesn’t print and never showed up in your move. Some answers travel. Some don’t.
The general point is that when you look at the rules a community lives by, the written rules are usually doing less work than you think, the conventions on top of them are doing more, and the conventions are often substituting for something else entirely. Some of the most consequential rules people follow are ones nobody wrote down — and the people those rules help most often don’t know they’re being helped, because they’ve never lived without them. You learned this the hard way at a left-turn arrow. Most people learn it the hard way somewhere.
With that, I leave you with this.