A Primer on Traffic Congestion

Looking at the root causes and potential approaches we can take to solve one of the biggest problems with modern transportation

In the US alone, 17.4 billion hours are wasted sitting in traffic. During this time, over 3 billion additional gallons of fuel are emitted into the atmosphere (which is ~2% of the 134 billion gallons of gasoline consumed by Americans each year).

Furthermore, traffic congestion worsens as cities grow. Considering by 2050 13% of the worlds population is expected to shift from suburban/rural areas to urban cities, traffic congestion is expected to increase at astronomical rates.

Take Los Angeles for example, a metropolitan area of ~90,000km2 which has more roadway miles than all of Canada (~10M km2). Traffic in LA is known to be deadly, with drivers spending on average 119 hours per year sitting in traffic (which is almost double the 66 hours drivers experienced in 1987).

This trend is hardly unique to Los Angeles, with all major metropolitan regions in the US experiencing the same fate.

Breakdown of Traffic Congestion

Traffic congestion can be split into two buckets, non-recurring congestion and recurring congestion. (Here’s a link to the full breakdown).

Non-recurring congestion (55% of all traffic congestion) occurs at unexpected times. This includes congestion derived from traffic accidents (25%), construction zones (10%), weather delays (15%) or certain special events which create a surge in travel demand (5%).

Recurring congestion (45% of all traffic congestion) takes place at regular periods during the day, which can be derived from certain bottlenecks on the road (40%) and poorly timed traffic signals (5%).

Since roadway bottlenecks are the largest sub-cause of traffic congestion, the next part of the article will focus on those entirely.

Under roadway bottlenecks, there are 2 buckets, increase of demand or decrease in capacity.

Capacity reductions are infrastructure/design related, with the most prevalent bottlenecks occurring at highway mergers, road-bridge lane merging and poorly regulated on street parking.

Demand surges are travel mode related, with the core reasons being extreme car usage and variation of travel demand throughout the day.

Considering 89% of congestion (in urban areas) is caused by demand surges, the following sections will focus exclusively on breaking down the causes behind increases in travel demand.

High car usage can be attributed to 2 main factors: cars are simply the most attractive (attractive = convenient, practical, fast, comfortable) mode of travel (especially in America), and that most urban areas are built around the car.

Part 1: The Zoning Problem

The first bucket, low-density (single-use) areas is a result of the way which we zone our cities. Single-use zoning (Euclidian zoning) is based on the premise that different land uses should be separated due to incompatibility/negative outcomes when combined (examples of land uses include residential, commercial, recreational, etc).

It also regulates the density, height and the lot size of a development (many other variables, these are just the core ones).

This makes perfect sense when put into context of what the Euclidian zoning system was built for & when it was built. It was constructed in the early 1910’s to account for the poor quality of life in city centers, which was influenced by the shadows of the astronomically tall buildings (especially in NYC) and the incompatible uses in urban centers (some cities used to have slaughterhouses next to a residential family home).

This notion of separation was further enforced in the 1930’s & 40’s when people associated certain minority groups with lower property values. This resulted in city planners & developers incentivizing single-family homes on larger lots, which the generally poorer minorities at the time couldn’t afford.

Both the separation of uses & single-family development further increases commuting distance between locations, making more sustainable options like transit & biking less attractive options for travel and placing the automobile on a pedestal.

While these issues which Euclidian zoning was built to address don’t exist at their extremes today, we still continue to use this outdated (and rather flawed) zoning system to plan our cities.

A Promising Alternative to Conventional Zoning

A new approach to zoning, called form-based zoning is an approach which considers both the form (design) and the use of the buildings in the context of the neighbourhood as a whole.

Form-based codes (FBC) also focus on street design, with the intention of making streets more viable for pedestrians/cyclists instead of leaving it to engineers who optimize roadways for traffic.

Another notable benefit of FBC’s is they are predominantly visual-based, making the zoning codes much easier to read, allowing for faster developer permit approval times and a better comprehension of zoning regulations among the general public.

While FBC’s are a promising alternative, they have some barriers to widespread adoption, namely their complexity to originally write & update.

A Couple of Examples

North Miami Beach, which was once an auto-centric suburb of Miami, has replaced its traditional zoning system with form-based codes and seen significant results (in terms of both transportation and land use).

A case study on one development in the city demonstrated a 9% reduction in total daily trips (total reduction of 227 trips, shifted from cars to other mode).

Another case study of transit-oriented development (not specifically on form-based codes) in Austin, Texas noted a 21% of reduction of peak hour traffic congestion.

Part 2: The Overconsumption Problem

Another core issue connected to increased travel demand is high car usage. In America, over 80% of commuters use cars to drive to work. America’s car-dependent lifestyle is no accident, its largely a result of how cities were planned.

One core reason for America’s car-dependence is the vast amount of road infrastructure built favouring cars. In America, there over 4.09 million miles of roads (Canada, which is >100M sqkm bigger in area than the US, only has 647,000 total road miles).

This sufficiently large road network makes alternative modes like biking and transit less feasible (transit commuted take on average~2X longer than car commutes), while increasing the overall desirability of cars.

However, the problem isn’t solely that there is an excess of roads, its that roads are heavily subsidized by the government. These subsidies are paid indirectly through taxpayer dollars.

A Harvard study found in Massachusetts alone, each taxpayer pays $1.7K/year on average to account for road building/maintenance costs (with the total cost amounting to over $4.4B/year).

The basic economic concepts of supply and demand indicate that if a good is in high demand and has a low price, it is bound to get overconsumed (run out of supply). In the context of roadway travel, overconsumption is traffic congestion.

Furthermore, America has an absurd amount of parking spaces (>2 billion parking spaces). Yes, 2 billion parking spaces for only 250 million cars. That’s over 360 billion square feet of land given to subsidized parking. The cost of this subsidy is $127B/year (2002), which is surely much higher today.

Parking not only costs taxpayers indirectly, it further incentivizes driving. Over 99% of car trips ended in a free parking lot.

In short, the problem is subsidized roads favouring car travel.

An Effective, but Controversial Solution

Congestion & parking pricing, a.k.a every politicians nightmare. While it has its downsides, congestion & parking pricing is the way forward to address the overconsumption problem.

The idea is to make drivers realize the true value of using a road by adjusting the price of using that road in hopes of managing travel demand. Parking pricing is the same idea applied to parking

Note: I’ll mainly focus on congestion pricing for the explanation of the bottlenecks for adoption.

Congestion procing has some technical issues, however the largest barrier to mass adoption is the political one. Congestion pricing is a political nightmare, especially in America’s auto-dependent cities.

While there are numerous arguments against congestion pricing schemes, the most notable ones (in a North American context) are: equity issues and lack of practical transportation alternatives to cars.

The first issue, equity, is based on the perception that congestion price is a regressive tax. And for the most part, it is, since a charge of $3/trip is a larger burden for an individual who makes $20K/year versus someone who makes $200K/year.

The second issue, lack of alternatives, is rooted in how North American cities are formed. A policy like congestion pricing in the context of a traditional auto-oriented suburb wouldn’t just limit car travel, it would impede travel as a whole.

These suburbs, which house 52% of the American population, are built around the car. This means people base their location choice of their home, work and other commutes based upon the cost of travel using a car (cost including both time and money).

The problem is, when making the aforementioned location choices, they don’t account for all the other hidden costs associated with an auto-centric life, including: the road/parking subsidy, the lost land value to roads, pollution costs, etc (view chart below) which are paid for indirectly through tax revenues/economic losses.

When congestion pricing converts these indirect costs into direct costs, it requires people to reconsider their location/commute choices based on the new costs. This is what people don’t like, therefore leading to heavy initial opposition to the policy.

However, this is only a problem because cities are built around the car. The cost wouldn’t be as severe if transit was more practical, or if most commutes were within walking distance.

The 2 major reasons for the poor alternatives to cars in the North American context are: the outdated zoning system and the travel demand favoring cars.

Simply put, the ROI of building car related infrastructure is unparalleled.

In the case where public officials are faced with the choice of building a transit line expansion or a highway expansion, the transit line expansion will result in marginal ridership increase, while the highway expansion will result in a noticeable improvement in traffic flow and number of trips taken.

While the benefits are only in the short term, as congestion re-emerges after a couple years, most governments simply rewiden congested road segments, further increasing the number of people who drive, resulting in more congestion in the future (and lessen the number of people taking alternative modes, like transit or walking).

There are many examples of this trend, most notably the Katy Freeway in Houston which got a $2.8 billion expansion to 23 lanes, which was completed in 2010. By 2014, congestion was up 55% from 2011.

Pricing Is Working for Other Cities

London deployed congestion pricing in its downtown area, seeing declines of daily traffic by 20% and travel speeds increasing 37%, with peak hour car travel decreasing by 30% and 50% in busses. This scheme generated over $100M/yr of revenue which was reinvested into public transportation/road infrastructure improvements.

New York is building out its own congestion pricing scheme, which is expected to generate over $1B/yr of revenue for to account for its degrading transit system.

The benefits of pricing are clear, however it will require both a collaboration between governments and private companies to build & push new technologies to address problems associated with congestion pricing policies.

It’s A Really Tough Problem, eh!

Overall, there is no one solution which will solve traffic congestion outright. There are many solutions which must work in tandem for traffic congestion to be minimized. However, with the right technology and political collaboration, traffic jams which are hours long could be unheard of in the future.

If you liked this story, I’d love to connect. Here’s my Linkedin and email.

A big AI and car guy. I write on transportation, urban development, deep learning and that sorta stuff.

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