Level of Service: Measuring Traffic Congestion

This article first appeared in the NMA Foundation’s Driving Freedoms Magazine Spring 2019 edition.

According to the latest census, 85 percent of all Americans travel to work by single passenger car or by carpool. Since World War II, land use and American culture have been built around driving cars from locations A to B. By design, the US is automobile-centric and has been since the construction of the interstate highway system was authorized by the Federal Aid Highway Act of 1956 during the Eisenhower presidency. Most people still rely on cars as their primary source of daily transportation.

Level of Service or LOS is a performance metric which started when the US began building freeways in the 1950s. LOS uses a scale of A to F based on an objective formula that tries to answer the question, “How much congestion are we willing to tolerate?”

LOS measures the delay experienced by motorists on a roadway or at an intersection of least delay (an A rating) through the most delay (an F rating). See below for details.

The LOS grade is used to communicate the potential impact from new development on a road or a street intersection, which is often also used to assess potential congestion in the 20- to 30-year timeframe of the development.

Up until recently, the LOS rating system had been used by traffic engineers to define problems and prioritize transportation system improvements. A LOS rating of D or worse usually meant that the road or intersection needed work and was a priority.

The moderate-to-liberal Washington, D.C. think tank The Brookings Institution has recently called for a change from the LOS rating system. In a post on its website:

The LOS rating system, though, is not just used as a descriptive tool. State and local departments of transportation and the Federal Highway Administration benchmark the success of regional transportation systems against the LOS scorecard. That means engineers, planners, and many other leaders target their priorities and investment decisions towards reducing congestion.

The irony of the LOS system is that it hasn’t solved congestion at all. In fact, it’s just the opposite: LOS keeps making traffic worse.

According to Brookings, major urban road mileage rose by 77 percent from 1980 to 2014 compared to 41 percent growth in the US population. That’s a total of 169,153 lane miles. As the number of lanes grew, people drove more and increased vehicle miles traveled by 146 percent during that period.

Critics call LOS mono-modal because it measures streets only by their ability to move vehicles and not by economic, environmental or social vibrancy. Many traffic engineers and city planners now consider the LOS methodology technically flawed and biased because it ignores other issues such as parking congestion, traffic accident rates, mobility issues for non-drivers, energy usage, vehicle emissions, physical fitness and increased consumer costs for car owners.

There has never been a national requirement or mandate to apply LOS standards. It has become a tradition, a convenient way to measure the traffic impact when evaluating a street or intersection design. With the advent of big data, cities are now looking more closely at LOS, especially if they have adopted a Complete Streets program.

Departments of transportation around the country are now adopting multi-modal LOS indicators based on Complete Streets policies, which refers to street design that accommodates diverse users and activities safely. Thirty-three state governments have adopted Complete Street policies with over 1400 US cities participating. Since 2001, advocates have also been pushing the Green Transportation Hierarchy:

  1. Pedestrians
  2. Bicycles
  3. Public Transportation
  4. Service and Freight Vehicles
  5. Taxis (and now ridesharing)
  6. Multiple Occupant Vehicles
  7. Single Occupant Vehicles

Now, the US Congress is getting involved in the issue. In early March, lawmakers introduced two bills (SB654 and HB1517) simultaneously. If passed, they would provide funding to five state DOTs and 10 Metropolitan Planning Organizations (MPOs) to apply accessibility metrics to decision-making and to measure access to destinations by various modes. This brings to the forefront the effort to apply accessibility to transportation and land use-decisions. Those metrics are also expected to improve modal choice and vehicle-miles traveled predictions.

More people equals more vehicle miles traveled, but should motorists be the ones to pay for all the changes that Complete Streets planners want to make to the transportation system? New York City may well soon become the first in the US to have congestion pricing/tolling when driving to certain parts of the city. Collected toll revenue will not only hurt the middle class and poor, but also businesses, and ultimately the consumer. Lawmakers say the funding will reduce congestion while at the same time help pay for the failing subway system that is over-capacitated and in poor physical shape. The money to pay for the system has to come from somewhere, but why tax motorists for public transit systems that can’t sustain themselves?

A Portland, Oregon member recently wrote to us with this observation: “Both the city council and mayor have said they want us out of our cars and will do what it takes to do that. Ironically, that same city council wants to raise the gas tax again. Why? Funding for pedestrian safety and more bicycle lanes. So they want to tax us more and take away more? The insanity is overwhelming!”

Level of Service Grading System

A – Free-flowing traffic at or above the posted speed limit

B – Reasonably free flow, traffic stream is slightly restricted

C – Stable flow, speeds decrease slightly with increased traffic volume

D – Approaching unstable flow with noticeable restrictions

E – Unstable flow, traffic is at capacity and moves irregularly

F – Forced/breakdown flow, more or less bumper to bumper, with frequent slowing

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