- The road system can be expanded to help improve access to rural and mountainous regions.
- New roads could include more experimental materials to help improve sustainability and resiliency.
- Expanding these roads has an estimated cost of $517 million.
Construction of New Roads
Roads in Puerto Rico, which were already damaged before the storm hit, deteriorated further because of the storm. Some roads were even completely washed away.  Roads near the coast and waterways are particularly vulnerable to flooding. Constructing new roads where they were demolished and fixing those that are in bad condition will aid in resiliency-improvement efforts with rural communities and across the island as a whole. The following approaches to road construction can help ensure that the roads in Puerto Rico are resilient to weathering and extreme damage and will allow for maintenance as time progresses.
As a long term goal, we propose expanding the road systems to provide greater access to rural mountainous areas, particularly in the case of blocked roads during and following storms. Ideally, all communities would have multiple points of entry and egress, to further decrease the probability of total isolation. For months after Hurricane Maria, many rural communities were impossible to access using roads. Food and water among other supplies had to be flown in. 
Roads must also have effective drainage systems to reduce damage from flooding and runoff. More specifically, it is important that roads are sufficiently compacted and that the shape of the road adequately disperses water from the surface.  Keeping this in mind as new roads are built will help improve flooding recovery and resilience.
Costs of road construction vary greatly depending on terrain. For instance, roads in rural areas cost two to three million dollars per mile, while roads in urban areas cost up to four million dollars per mile.  Additionally, construction costs can increase sharply in mountainous regions.
Building new roads can happen in phases. We have outlined a potential first step in building new roads throughout Puerto Rico. Using distances between fifteen mountain municipalities.  and assuming the upper-end of per mile costs of building new roads, we estimate that it would cost $518M over about 173 miles to implement a first phase of building new roads. This estimate does not consider the price of using experimental materials (discussed below) as they are still in development and do not have a reliable cost estimate. This rough estimate can provide a basis for estimating how much it might cost to build new roads in other mountainous and rural communities in future phases of implementation.
Also, in 2018, the Puerto Rican government has set out to repair about 780 miles of road and contribute $402M in the project, with the federal government contributing another $250M, for a total of $652M invested in this repair effort.  There is also a $130M annual reserve. 
Additionally, a timeline of implementation can go a long way for minimizing financial burden. Even implementing part of this proposal now and gradually adding miles of new road will help people travel safely and efficiently.
The Puerto Rican government should consider new alternative road-building materials in the effort to create a more robust road system. In this section, we discuss innovative sustainable materials that we think could help in the long term. Puerto Rico is also in the process of repairing roads as mentioned above under a $652 million budget,  and we emphasize that these new materials are most practical when discussing plans for completely new roads or road repairs in the distant future.
These materials must be durable, cost-efficient, and easy to maintain. Currently, roads in Puerto Rico consist largely of low-quality asphalt, which contributes to the fragility of roads in the face of disaster.  Additionally, Puerto Rico’s climate would naturally cause even high-quality asphalt to soften. However, the alternative, concrete, is already responsible for 5% of global emissions, damages topsoil, and is prone to cracking and scaling.  These cracks and scales are only further exacerbated by hurricanes and storms. Clearing and repairing concrete also generally takes a longer time than for asphalt.
Many institutions are supporting research into sustainable road materials, and many of these new ideas should be considered for both resiliency and recovery stages in Puerto Rico. Recently, groups including MIT’s Concrete Sustainability Hub (CSHub) have developed several cost-saving, effective, and environmentally friendly alternatives to traditional concrete and asphalt.  One specific research group in the CSHub has explored minimizing thermal cracking in concrete pavements, encouraging engineers to consider changes in environmental conditions, as has been the norm in past concrete innovations.  This method encourages engineers designing new types of concrete to focus more on making sure that the new alternatives are resistant to large changes in their environment. For instance, fluctuations in temperature typically cause materials to expand and contract and can affect the integrity and longevity of the material. If extra attention is given to the transient period during concrete designs, MIT scientists contend that the concrete would be more resilient during temperature fluxes. This is especially pertinent for addressing resiliency in Puerto Rican roads with changes in average temperature due to climate change and, near cities, the heat island effect, wherein urban areas experience warmer temperatures than the rural areas around them.  If roads have fewer cracks and are more stable to begin with before a hurricane hits the island, they will likely withstand hurricane damage more than their already-cracked counterparts.
Another way to build more sustainable and adaptable roads is through the use of alternative materials and processes. For example, “grasscrete,” which involves laying concrete flooring, walkways, sidewalks, and driveways in with openings for grass or other flora to grow, is highly promising, especially for post-hurricane wildlife conservation. 
Blast furnace slag, demolition rubble, crushed concrete, and bottom ash from municipal solid waste incinerators can be used as alternatives to traditional concrete, and would otherwise not be reused.  For Puerto Rico specifically, using demolition rubble and crushed concrete would be an efficient option for recycling the rubble generated by the hurricane. This way, the debris would both be cleaned and the roads repaired via one sustainable effort. However, this requires additional investigation, as current implementations of recycling have high transportation costs and uncertain material performance.
Open-graded friction course pavement and porous pavement are newly developed alternatives that let water percolate through the road and safely run off beneath it. They have an installed artificial layer of rock beneath the road to allow runoff. 
For post-hurricane efforts this is crucial, as flooding can be a major threat to citizen safety and an obstacle for post-hurricane transportation, as well as a threat to the natural wildlife. If the roads can be designed with flooding specifically in mind, the effects would trickle down to more widespread sustainability. We propose that new roads be comprised of porous materials with a top layer porosity score of at least 0.18 and a reservoir stone bed layer with porosity greater than or equal to 0.32.  The porosity of roads is key to decreasing runoff rates and, as a result, flooding.
Although it is important to recognize that the concrete industry is currently a major component of Puerto Rico’s economy,  transitioning to the production of these alternative materials could prove to be just as viable. We support further investigation into the degree to which these alternative materials will cut costs in other sectors (energy costs, maintenance, etc. and whether, though they might be expensive in the short term, they may result in budgetary gains in the long run.