Roads, access, and emergency response

How assessment products can help keep emergency managers informed

It’s critical that emergency managers understand road accessibility and response drive-times in their planning.

When hazards such as floods, landslides, or wildfire impact roadways, chances are the most time-efficient emergency response drive-times are going to change. In worst-case scenarios, there could even be complete loss of access to some areas — those with single points of road access or, in some regions, the most vulnerable communities — from inundated or damaged roads.

So we came up with a few questions that we thought a community planner or emergency responder might ask about vulnerability and road accessibility. Then, using GIS, we modeled the results.

We began the assessment using the roadways of the Triangle Region (Raleigh-Durham-Chapel Hill) in North Carolina, the locations of fire stations as the points from which emergency responders would access roadways, and the 500-year floodplain as the hazard or barrier.

Our study area: The Triangle Region of North Carolina, in the center of the state. The Triangle is made up of the region’s three major cities: Raleigh, Durham, and Chapel Hill.

Question 1. What are my emergency response times in a business-as-usual scenario?

The first question looks at the normal response drive times of three, five, and eight minutes from fire stations when there is no hazard or barrier impacting the roadway. These thresholds are often used in emergency response planning. We asked this question to help develop a baseline understanding of accessibility and response scenarios.

This regional map seeks to answer the question, “What are my emergency response times in a business-as-usual scenario?” (Map: NEMAC+FernLeaf)

Let’s zoom in and take a closer look at one area:

U.S. Route 501, shown in purple. (Map: NEMAC+FernLeaf)

U.S. Route 501, or Durham-Chapel Hill Boulevard, is a primary transportation corridor connecting Chapel Hill and Durham. Community residents rely on this corridor for access to education, health care, and work. Being a priority roadway, transportation planners in the Triangle region have identified this corridor as the primary, aligning route for the upcoming light-rail line.

Even under normal conditions, many of the residential areas along this route have five- and eight-minute response times (above).

Question 2. What are my emergency response times in a flood event?

Next, we explored how the drive-times would be altered from inundation in a 500-year flood event—an event that has a 1 in 500 chance of occurring in any given year.

This regional map seeks to answer the question, “What are my emergency response times in a 500-year flood event?” (Map: NEMAC+FernLeaf)

Again, let’s zoom in and take a closer look at the U.S. Route 501 corridor:

How have response drive-times changed when considering the possibility of a 500-year flood event? Notice the residential areas that go over the 8-minute response time in grey. While much of the roads near fire stations aren’t impacted, those neighborhoods nearest the creeks do see change. (Map: NEMAC+FernLeaf)

Despite this area being close distance to many fire stations, a 500-year flood event has the potential to change response times. Results of the analysis show that potential flooding around Sandy and New Hope Creeks along this section of the U.S. Route 501 corridor could increase drive times to more than eight minutes in many nearby neighborhoods.

A key result: response times can be impacted even in areas that are not particularly prone to flooding.

Question 3. Who becomes isolated in a flood event?

Which neighborhoods or community resources face potential loss of access and isolation from emergency responders? This part of the analysis identifies roads that are potentially isolated due to a 500-year flood event.

This regional map seeks to answer the question, “Who becomes isolated in a 500-year flood event?” (Map: NEMAC+FernLeaf)

And a closer look at the U.S. Route 501 corridor:

Much of U.S. Route 501 is shown to be isolated from an eight-minute emergency response drive time or inundated by a potential 500-year flood event. How could this impact access to other resources, such as school, work, or healthcare? (Map: NEMAC+FernLeaf)

The model suggests that many primary transportation corridors, such as U.S. Route 501, have the potential for inundation…and thus also the potential for isolating certain neighborhoods from emergency response.

That’s the model. But what does this really look like?

Hurricane Florence made landfall in September 2018 as a Category 4 storm. As it moved inland, it eventually approached the Triangle Region, pouring an estimated six to eight inches of rain in the areas surrounding the U.S. Route 501 corridor we’ve been examining.

This precipitation event caused the creeks to rise, inundating the highway and leaving many residents potentially isolated from emergency response—while likely increasing drive times to surrounding neighborhoods.

Left: An automobile braves the flooded roadway on U.S. Route 501, a primary roadway connecting Chapel Hill and Durham. (Photo: Shawn Rocco) Right: 3D representation of the section of U.S. Route 501 we’ve been examining, inundated with a potential 500-year flood scenario. Notice the street sign over the northbound portion of the highway and the U-Haul facility behind it — then look again at the photo at left. (3D rendering: NEMAC+FernLeaf)

Ultimately, emergency managers can use this information to develop resilience strategies.

Understanding vulnerabilities in a community’s road network before an event can reduce the overall impact and provide emergency managers with better information for response and recovery.

There’s no such thing as a stupid question

What other hazards or barriers exist in your community that could potentially interrupt access to homes, jobs, food, public safety, or health care?

What other services or assets are important to your community being able to respond and recover from an event?

What type of economic impact would an interruption have?

This analysis is just the beginning. There are certainly many more questions that can help communities build resilience to these events.

There’s a lot more work to do to address accessibility issues.

Analysis notes and other considerations

This particular analysis was performed to demonstrate the methodology and should not be used to make actual response decisions. There are many other variables to consider when modeling connectivity and accessibility networks. Here are a few worth mentioning:

• Many locally created street GIS network datasets lack correct topology to perform this type of analysis—such as disconnected nodes, missing intersections, and missing road directionality. Having a robust GIS dataset is often a challenge.
• Bridge height and structural condition is critical in understanding potential inundation events — a robust analysis should include these bridge attributes.
• Road centerlines were used in this analysis. It is possible that roadways become only partially flooded, allowing emergency responders to go around the the flood barrier.
• Flood mapping extents were considered equal in this analysis. Flood inundation depths should be considered in future analyses.