It might be time for your streets to go gradeless.
Level of Service (LOS) is the one thing you should know about traffic engineering.
In an effort to prevent vehicular congestion, experts prevent human activity.
You’ll hear me and many other urbanists rant about how traffic engineering ruins mobility. But how does engineering analysis make transportation worse? I realize it sounds absurd. So I, your former traffic engineer, will lay out the single biggest way that traffic engineers make life miserable for people of all ages.
Level of service (LOS) is the standard method for measuring the performance of an intersection.
The LOS methodology comes from the Highway Capacity Manual, originally published in 1950. Community streets should never function like highways, so the name alone should already raise suspicion. Intersection performance is judged in terms of vehicular delay—in seconds. It has nothing to do with the level of comfort experienced by human beings using any other form of transportation.
It’s worth pausing to reflect on that, because walking and bicycling are the fundamental modes of travel but they aren’t part of the fundamental engineering analysis.
Illusion of objectivity
A grading system of A through F suggests objective analysis. It’s smartly compared to school letter grades, because that’s something everyone is familiar with. If you got 5 wrong answers on a test out of a total of 10 questions, you knew 50% was an F. But in traffic analysis, the performance metric is how many seconds cars wait (or don’t wait) to go. There’s no consideration to overall travel time, safety, or ability of anyone outside of a passenger car.
The average person attending a public hearing has been trained since early childhood that A is good and F is bad. So even if they don’t like the idea of the local government seizing their front yard in order to widen a street to improve LOS, normies assume it’s for the greater good. Such is the treacherous nature of LOS.
If traffic engineers were crystal clear about their analysis, it would sound like this:
During the busiest hour of the day, the average driver waits 30 seconds at the stop sign. We give that a grade of D. The other 23 hours of the day don’t matter.
The transportation department is guessing that 20 years from now, the average driver might have to wait an entire minute at the stop sign. We give that a grade of F. The other 23 hours of the day won’t matter.
If only transportation experts articulated their methodology with unbiased, objective language. As soon as the words came out of their mouths, the snickering would erupt into jeers.
LOS is immune to context.
It doesn’t matter if it’s applied to a historic downtown, a neighborhood street, or a rural village. Infrastructure designed around LOS grades serves one purpose: speed up motor vehicles. Standard intersection analysis is a danger hiding in plain sight. Intersections are expected to have good grades during the one or two busiest hours of a day.
Here’s what happens when traffic engineers analyze morning rush hour:
A central business district includes office towers, coffee shops, and some hotels. The employees generally arrive between 7:30 and 8:30 AM.
Almost all of the car traffic flows in from one direction because the transportation department has widened the primary road several times without giving motorists any other access options.
Concerned about the bottleneck where motorists turn left into the central business district, the transportation department reports that the intersections operate with a “poor” LOS E or F during the morning rush hour. (Meaning the average driver waits a minute to get through the light.)
The transportation department builds more lanes, so the average driver doesn’t have to wait a full minute at the light. For 23 hours a day, the new lanes are noticeably empty. And for all 24 hours in a day, the intersection is now more dangerous for people trying to walk across the intersection.
The damage isn’t done, because the traffic engineers also analyze the evening rush hour. Commuters driving out of the central business district between 5:00 and 6:00 PM can’t be allowed to wait an entire minute at the light, so more lanes are added.
Do you see why traffic engineers ruin communities? Every single intersection is analyzed and graded based on seconds of delay for drivers. So every single intersection “needs” more lanes to pump as much car traffic as quickly as possible through an intersection. Anything else (moms pushing strollers, grandparents with canes, kids on bicycles) interferes with LOS.
Here are three important questions rarely pondered by a traffic engineer:
Is slow-moving car traffic ever safer than fast-moving traffic?
Do we have any obligation to provide safe and convenient access for non-motorized traffic?
Do wider, faster streets have an economic benefit in the central business district?
When they do wrestle with those questions, they either become an outlier in the industry or leave altogether. Let me know if you need help conversing with a traffic engineer. It’s one of my favorite pastimes.
Comedian Louis CK has something to say about traffic engineering’s use of LOS.