# Available interventions

An RDM analysis typically begins by identifying available options. To reduce losses linked to the disruption of part of the road network because of a disaster, policy makers have two sets of choices: intervene after the disaster hits (reactive), or try to reduce possible impacts with proactive interventions beforehand. Proactive interventions include all those that reduce or eliminate disruption losses, while reactive interventions include rehabilitation or reconstruction of the affected road. The advantage of the latter is that no resources are directed where they may not be needed. But intervening after a disaster may be more costly than preventing it. In particular, rehabilitation can take time, especially for roads managed directly by the government, so the costs for the economy at large may escalate.

We compared several proactive options with a reactive one, in which the government or concessionaries rebuild the same road after a disaster ruined it. We considered the following proactive options:

- _Interventions on the critical road._ The first option is to maintain the road more frequently. Generally, road authorities perform two types of maintenance: routine and periodic. Routine maintenance involves all sorts of small interventions on a road and can be carried out once a year or more often, depending on the weather, on the materials used, and on the traffic. Periodic maintenance generally occurs every five years and includes major rehabilitation works. Proper maintenance and frequent cleaning of drainage structures can significantly reduce the time water remains on a road – and in its turn, reduce the overall damage to the infrastructure. As intervention, we considered doubling the frequency of periodic maintenance, and assumed that it divides by three the length of a disruption due to flood.

- The second option is to upgrade the road, which may involve adding tunnels or elevating a road – depending on the topography of the area. Such work can be very costly, but we assume that it would make the road resistant even to 100-year return period floods. The costs we use are based on discussions with stakeholders.

- _Adding redundancy by upgrading an existing alternative to the first-best route_ . For each link disrupted, we already identified second-best routes as alternatives to the lowest-cost routes between all ODs. So, we explored the option of improving the roads most used by these second-best routes. For instance, this could imply transforming an existing secondary road, or an unpaved road, into a primary paved road. We considered two possible ways of adding redundancy: a large-scale increase in redundancy, where all road segments used for second-best routes are upgraded to primary paved roads, and a more targeted increase in redundancy, where only 30 percent of alternative roads are upgraded to primary paved roads.

These interventions have different capital and maintenance costs (see Table 6).

# Uncertainties

We considered four types of uncertainties that can affect the choice of the best intervention. Some are related to the impossibility of predicting their values; others to data gaps. The uncertainties are the intensity, frequency, and duration of climate-related events; the structural impact of water levels on the 11