Level of Service: the destructive force behind deadly street design

Traffic engineer works tirelessly to save motorist from waiting more than 30 seconds.

Traffic Engineer: "We found that drivers had to wait a whole minute at a red light. That's unacceptable. We're going to add another lane in each direction to minimize delay."

Normie: "A minute?"

Traffic Engineer: "A whole minute. Unacceptable.”

Source: Virginia DOT, adapted from Highway Capacity Manual

When I’m baiting status quo defenders on Twitter, I don’t lead off by telling them I began my career as a traffic engineer or rattling off credentials. My work experience is secondary. The primary issue is the fact that standard traffic analysis starts by rewarding dangerous design and then patches on some safety bandages from time to time.

Level of Service (LOS) is used to grade intersections as acceptable or unacceptable. It’s the key to traffic analysis and it has nothing to do with safety. LOS is a metric about how long you sit at a light, a stop sign, or how long it takes you to zip through a corridor. The longer it takes you to drive, the “worse” the LOS.

The letter grade system was a marketing stroke of genius, because it mimics school. What the experts don't tell you is that LOS A can be deadly and LOS F can be delightful. What you see below is a typical intersection that has been expanded over time to “improve” LOS. Each new lane encourages faster driving, exposes pedestrians to more hostility, and increases the likelihood of crashes.

The alternative to modern traffic engineering analysis is simple: abolish Level of Service. We can’t go back in time to prevent millions of senseless injuries and deaths, but we can stop using this ridiculous metric at any time.

You may encounter traffic engineers on social media or IRL throwing tantrums: "How dare you say we don't use engineering judgment without providing some evidence!" 😭😡😭😡

Here’s some evidence for you to share. If an expert can’t look at these “acceptable LOS” streets without seeing a problem, that expert is part of the problem.

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