More trees should come from highways
More trees are needed within the city, not along its highways. Finding where to plant 1,500 trees in a city to offset the impact of a highway project does not make the headlines of a city newspaper. The discussions tend to focus more on what are considered bigger issues, such as needs for highways, road upgrades to lower traffic and commuting times. Is it possible to conceive a highway project that creates a long-term net positive gain in a city and also helps adapting to climate change?
Many urban municipalities are expanding their highway infrastructure to cope with increasing volumes of cars and trucks. Highways are believed to increase efficiencies in transportation and productivity, and as such, cities are investing billions of dollars to improve and develop road infrastructure. Mexico City has already built a second story beltway and is considering a third level, while Sao Paulo is finishing its outer beltway, the largest road investment in the state to connect the airport, the major Santos port to the Mercosul region without crossing the city and creating traffic congestion.
This improvement would allow Sao Paulo’s productivity to increase as goods are getting in and out faster, and better connectivity is injected in the region, but many local economists point out that the beltway is irrelevant in its purpose of reducing traffic volumes as it would incentivize its use and would only lessen traffic for couple of years. While highways can reduce traffic significantly for few years, there are many environmental, economic and social impacts from these types of infrastructural investments that are not reflected in the projects’ total cost. To get permission to build, the environmental licenses typically look for the direct impacts related to the construction of the project, in the terms of fallen trees, demolitions, noise, and pollution.
Yet, not everyone is in agreement with the costs that these developments have on the environment. For example, various experts condemn these projects as city fabric disruptors as neighborhoods are destroyed to give way to cars. More highways mean more cars and more pollution. In Sao Paulo the daily total percent of all motorized journeys has increased from 48% in 1997, to 53% today. The expected economic flux in citywide productivity will also allow more citizens to be able to purchase cars in the future. If a city is investing more on highways than on public transit, it is incentivizing the use of automobiles instead of discouraging car use.
All highway infrastructure projects have an impact to the environment. The environmental impact that a highway infrastructure project has involves degradation and air, noise, and water pollution from the construction phase till the end of its lifecycle. Many countries employ impact mitigation hierarchies to deal with infrastructure projects that do not account for the environmental cost of highways or the cost of the whole highway lifecycle. These mitigation hierarchies in general are simplified as an inverted pyramid with different levels of mitigation: first prioritizing impact avoidance in the design phase, consequently reducing the severity of impacts, remediating the project’s impact, compensating for unavoidable impacts, and lastly enhancing environment to achieve a net positive gain.
Trees are handled as sustainability tokens for highways. For highways unavoidable impact, the usual compensation measure is reduced to planting specified number trees along highways. But planting trees along highways does not compensate for the environmental degradation wrought on by roads. The areas along highways are inhospitable environments to most trees species; in fact it is considered that 5 years is the average lifespan of a highway tree. To make the highway trees thrive in these conditions it requires long-term maintenance, which is often disregarded and increases the costs of the project. As a result, when trees do not survive, their carbon offsetting properties are not real.
Trees can benefit more inside a city that lacks green areas than along its highways. Cities lacking open green areas must consider to offset highway impacts with an allocation strategy that includes offsite environmental measures as part of increasing the project’s environmental value. This strategy can help influence investment behavior by considering external costs of highways impacts and their possible net positive environmental gains in the city.