The road to hell is paved with asphalt
January 15th, 2024
Most roads are paved with asphalt. Unfortunately, there are a lot of problems with asphalt. Bricks, cobblestones, and pavers are often much better options, because:
1. Asphalt degrades fast, so once you account for maintenance, it's more expensive it first appears
Asphalt ages and falls apart quickly. It needs to be replaced after 10-15 years and starts looking pretty crummy well before then. It forms potholes and cracks quickly, especially in extreme climates. It's cheaper to install upfront, but over time, it is much more expensive.
2. Asphalt is expensive to change, and it scars too
Whenever a construction crew needs to do underground work beneath an asphalt road, they have to rip up all of the asphalt and then patch it back up afterwards – and it's never as smooth as it previously was. This adds cost and time to any road project, which usually isn't taken into account when the road is originally constructed. If they were, asphalt wouldn't look like such a cheap option.
With materials like brick or cobblestone, crews can easily lift individual stones to access below, then replace them once finished. "When the construction crews complete their underground work, the gravel bedding layer can be re-compacted and the original pavers reset," explains Preservation Chicago. "It is often impossible to see where the pavers were disturbed."
3. Asphalt absorbs heat
Asphalt absorbs a lot of heat. On hot days, asphalt can be 25℉ warmer than other surfaces nearby!
Asphalt doesn't just make it less pleasant to walk on top of them on a hot day – it also heats up nearby buildings as well, increasing energy demands for AC.
Pavers tend to do better in hot weather because the gaps between each piece allow for a small amount of airflow, releasing heat more easily. This higher ratio of surface area to volume makes a big difference.
That said, not all pavers are created equal. Lighter colored bricks stay much cooler than denser concrete or terra cotta pavers. Within cobblestones, smoothed limestone reflects more sunlight and heats up less efficiently than trap rock or river rock. And among slabs, light-hued granite withstands warming better than slate or bluestone which can get quite hot in full sun. Porosity also plays a role, with perforated Belgian blocks transferring heat faster than permeable limestone.
4. Asphalt cracks in the cold
|Asphalt gets hard and brittle in the cold. This makes it harder for asphalt to handle the stress from cars driving over it. Asphalt also shrinks in the cold, adding to the stress. This results in cracks in the surface, allowing water in. Water expands when it freezes, compounding the damage. Asphalt is a particularly bad choice for places with freezing winters.
Modular surfaces handle cold weather better, because they are made up of many smaller pieces that can move slightly when the ground freezes and thaws. This movement helps prevent cracking. Avoiding cracking means that water is less likely to get into the material in the first place, which prevents the worst of the damage.
5. Asphalt is ugly
Asphalt isn't very attractive, even when it's fresh, and it only gets uglier over time. It may be cheaper upfront than other surfacing materials, but the cost-cutting shows. Choosing a cheap material sends a signal that this is a lower priority space than other parts of a community.
Alternative materials give streets more charm. Unlike asphalt, they actually become more lovely as they age – over time, they develop even more personality as moss or lichen finds nooks to take hold. Plus, they're more likely to be made of local materials.
6. Asphalt has nasty emissions
|Asphalt releases harmful emissions like volatile organic compounds (VOCs), sulfur dioxide, and fine particulate matter when it's produced and laid down. These emissions contribute to air pollution, which can lead to breathing problems and environmental issues like smog and acid rain. Making asphalt also releases carbon dioxide, a greenhouse gas that contributes to climate change.
The process to make concrete or brick pavers typically releases less VOCs and particulates. Since installing pavers doesn't need as much heat, it uses less energy and results in lower carbon dioxide emissions. This makes pavers a more environmentally friendly option in terms of air quality and reducing greenhouse gases.
7. Asphalt has bad drainage
Asphalt is an impervious membrane that sheds water rather than allowing it to permeate into the ground. Even shallow puddles can linger for prolonged periods on asphalt. This contributes significantly to flooding issues, as the water has nowhere to go but overflow curbs and accumulate elsewhere.
These drainage problems are exacerbated by asphalt's tendency to crack and form pitted potholes over time. Instead of shedding water evenly, cracked roads effectively funnel moisture directly into the ground below at an unnaturally rapid rate.
Pavers are made to slowly absorb rainwater. Their interlocking design includes small gaps between each unit that allow rainfall to seep into the ground below instead of gathering on top. This helps drainage happen like nature intended, reducing and slowing down lots of runoff. Rather than overwhelming drains and sewers, the moisture gets safely absorbed through the porous system.
Different modular materials have different levels of porousness, but they almost all have better drainage performance than asphalt.
This is not to say that asphalt is always the wrong material. It sets quickly, it's easy to repair, and it's cheaper upfront – it's a great tool to have in the toolbox, especially for regions with moderate climates. But 93% of roads are paved with asphalt! I simply think that it's way overused, and on the margin we should look to other materials, especially residential and side streets.
The road to asphalt is paved with incentives
Given all of the downsides of asphalt, you might ask "why is asphalt so pervasive if there are better options out there?" A lot of it comes down to cashflow. Cashflow is one of the biggest challenges in real estate development, since – it's a business where you invest a lot of money upfront and then earn it back over time afterwards.
Developers are often motivated by short-term incentives when choosing materials for construction projects. They need to manage immediate expenses and ensure the project is completed within budget.
Moreover, when a developer builds a project to sell rather than to rent long-term, their responsibility ends once the units are sold. This means they aren't directly affected by the long-term maintenance costs. Similarly, city officials elected for specific terms might prioritize immediate cost savings over long-term expenses. They are more likely to get reelected for lowering the city's expenses this year than for lowering its long-term liabilities, which only show up decades later.
By contrast, if developers retain long-term responsibility for their projects—such as by renting out units instead of selling them outright—they would have a direct interest in reducing long-term maintenance costs. This change could encourage the use of more durable, cost-effective materials in the long run, benefiting both the developer and the tenants. The dynamic of rentals results in a win-win scenario, with lower long-term expenses for the developer and improved quality of life for the tenants. (If you're interested in learning more about why a developer might choose to rent or sell a project, here's a post that dives into that topic.)
Design tradeoffs of bricks, cobbles, & pavers
Modular materials have design tradeoffs too, of course. One common downside is that they can be bumpy to bike on. However it is possible to find options that give a smooth ride, if you look for it. Here are two examples I've seen in person:
Modular materials also tend to reduce traffic speeds, since the create a surface that is not as seamless as fresh asphalt or concrete. In one brick installation project, the average speed dropped from 41 mph to 29 mph. This represents 30% decrease in speed, and the risk of death when a pedestrian is hit by a vehicle is approximately 4x higher at 40 mph versus at 30 mph.
Of course whether this reduction in speed is a good thing or bad thing just depends on the context in which you're using it. It's great for residential side streets and commercial shopping streets, because you don't want cars racing around those places anyways. However on major arterials and highways, it wouldn't work so well, because the purpose of those roads is to move people as quickly as possible.
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We need to stop planning project primarily by spreadsheets, where the dominating inputs are costs you can measure easily. There are factors that are not reflected in those calculations that not only affect the quality of the place you're creating, but also the financial burden that the community will have to bear for decades down the line.
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