A strategic switch to biking would dramatically reduce the depth of roads, saving untold billions over the next generation.
A recent McKinsey report discussed an emerging revolution in road construction—one of the more stagnant sectors in infrastructure. While the article delved into artificial intelligence (AI), digitization, and the impact of autonomous vehicles on road width, it did not mention road depth.
Biking during the pandemic has not only been a welcome reprieve from public transport, but it has also demonstrated its considerable health, environmental, and time benefits. A steady increase over the years has been met with a tidal wave of interest in just months. Biking’s traditional benefits aside, surface thickness is perhaps the biggest asset of a bike lane and could potentially save the United States billions of dollars annually.
Road Purpose and Cost
The majority of bike lanes come as "add-ons" for main arterial roads used by cars and trucks, allocating a small portion of the road, either concrete or asphalt, to bikes. For those not fluent in "roadspeak," it is also increasingly common to see "road diets," where a four-lane car road is adjusted to add bike lanes and a middle lane while reducing to two lanes for cars.
To give road cost context, the U.S. Department of Transportation estimates that one lane of a mile-long road to reconstruct an existing lane in an urbanized environment costs the following.
|Type of Urban Environment||Reconstruct Existing Lane||Resurface Existing Lane|
Reconstructing existing lanes for a four-lane, five-mile road in a large, urbanized environment (nearly $3 million x 5 miles x 4 lanes) is over $58 million. To resurface those same lanes would cost about $17.9 million. That certainly is not cheap.
In the future, the United States will move increasingly away from cars and individual transport to lighter, more agile transportation modes. This mix will include high speed solutions, such as rail or potentially even a hyperloop for longer distances and individual modes of transport such as (electric) bikes, motorcycles, or scooters for shorter distances. Even a gondola would have a potentially smaller impact than roads—you wouldn't need any roads, although you probably couldn't bring your bike along.
Not only are bikes significantly lighter and thus less damaging to roads, they also do not come with the constant drip of fluids from cars in traffic, which breaks up asphalt quicker over the long-term.
Roads—Load, Class, and Width
For many urban (and suburban) options, particularly when trucking is involved, concrete is the surface of choice, and it should remain so. While it is significantly more expensive, it lasts up to 40 years, much longer than asphalt’s 3- to 5-year lifespan.
Both concrete and asphalt roads come with a considerable layer of aggregates, which serves as a base under the concrete or asphalt. Road thickness additionally depends on the soil type as well as function—residential streets, collector streets, or arterial streets, the latter of which is the busiest and accommodates heavy truck traffic.
The Asphalt Paving Association of Iowa provides a substantial overview of the class or roads depending on traffic:
- Class I — (Very Light) Less than 50 autos per day, less than 7,000 heavy trucks expected during design (construction) period. Examples of this class include golf cart paths, sidewalks, and bicycle paths. The depth here can be as little as three inches for asphalt concrete pavements.
- Class II — (Light) Up to 200 autos per day, 7,000 to 15,000 trucks expected during the design (construction) period, examples include residential streets, rural farm roads, and parking lots of less than 500 stalls The depth here must be at least five inches for asphalt concrete pavements—two-thirds more than bike paths.
- Class III — (Medium) Up to 700 autos per day, with 70,000 to 150,000 trucks expected during the design (construction) phase.
- Class IV — (Medium) Up to 4,500 autos per day, with 700,000 to 1,500,000 trucks expected during the design (construction) phase. Examples of this include urban minor arterial and light industrial streets as well as rural major collector and minor arterial highways.
Classes extend up to class Class VI, which include airport runways.
Given that most roads are Class II and above, there is substantial savings in building Class I roads to focus on cycling.
In addition, the average width of a car lane in the United States is 12 feet while the average bike lane is five feet when next to parked cars or just four feet when adjacent to a curb. With just one lane of road for cars, cities could easily have two lanes for bikes.
The Externalities of Driving Are Increasingly Visible
Public awareness is finally factoring in the externalities related to driving. Pandemic aside, which may produce a blip perhaps back toward individual car travel due to fears of infection and migration to suburban locations, consumers are seeing the growing disadvantages of car ownership:
- Upkeep — cars as a liability, standing still most of the day, with substantial residual costs around maintenance, gasoline, and insurance.
- Commuting — some workers have been teleworking, translating into less need for a car.
- Parking — with parking minimums increasingly called into question, no "free" parking spots will be available with each housing unit.
- Environmental health — any city’s population will be healthier after limiting the number of cars on the road.
In addition, the financial savings and physical impact of not having to lay down Class II car lanes would be enormous.
The embodied energy of road construction also plays a role, with the hundreds of back and forth trips of trucks hauling asphalt, aggregates, or cement. Embodied energy is the sum of all the energy required to produce any good or service, considered as if that energy was incorporated or embodied in the product itself. The embodied energy of building a Class I cycling road is much smaller than a Class II car road— much less hauling, spreading, and compaction equipment is needed. Material costs aside, the labor costs and construction time will be much shorter as well.
To put it in perspective and highlighted above, Class II estimates include 7,000–15,000 trucks during the design/construction phase. Class III estimates 70,000–150,000 trucks again during the design/construction phase. In comparison, Class I roads for bikes need less than 7,000 trucks.
For new neighborhoods, the economic value of pavement choices can be significant. Local governments should avoid the construction of one-foot thick roads, instead prioritizing bike lanes with one truck and car accommodating road allowing for deliveries. With the savings of not having to create Class II roads for an entire area, developers can pass savings onto citizens and increase livability by planting trees, creating community spaces, or building more (affordable) housing. By reducing a street’s footprint, prioritising bike lanes over Class II roads would also reduce the heat island effect, which exacerbates the effects of climate change.
Marketing the Hidden Value of Biking
It would bring no greater value to the United States than having a core of America's best marketers to communicate the billion-dollar advantage of biking. Biking's environmental, health and financial positives have long been noted—as long as they are safely kept away from cars.
Much has been accomplished, but much still needs to be done. Road diets aside, what are the scenarios in which we leave cars in the rearview mirror, adopting a nimbler system of cycling routes?
A road’s heavy load and costs reflect the car as the traditional 20th century transport option. This makes a 21st century lifestyle on two wheels that much more appealing and valuable. The business case is solid. Now is a defining moment—our commitment to building Class I roads for micromobility and retiring some Class II roads. It would save billions of dollars and make all the sense in the world, now and well into the future.
Richard Dion works in the Governance and Human Rights Unit at GIZ, the German Corporation for International Cooperation GmbH.
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HUD's Office of Policy Development and Research
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HUD's Office of Policy Development and Research
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