By Deputy Fire Marshal Rick Fluegge and City GIS Developer Sandy Gagné
Traffic calming devices, such as speed humps, have been used for several years in the city of Charleston, South Carolina, to help reduce speeds and lower the potential for crashes and injuries.
These devices are typically installed in residential neighborhoods along longer stretches of straight roadway. Drivers generally must slow to 15 mph or less to cross them safely. Although the intent is to reduce routine traffic speeds, each device can also affect emergency response, adding approximately 10 seconds to travel time.
As speed humps became more popular throughout Charleston, their cumulative effect on emergency service delivery required closer consideration. The city needed a way to evaluate new requests while accounting for response times, existing traffic-calming devices and established installation requirements.
Understanding speed hump design
The design of the speed hump will impact the safe speed at which any vehicle can safely cross it.
Charleston’s program generally uses parabolic or flat-top designs. Parabolic speed humps gradually rise to a height of about 3 inches and extend approximately 14 feet. Flat-top devices are similar but include a 10-foot-wide flat section that can also accommodate pedestrian traffic.
Traffic-calming programs in Charleston are regulated either by the South Carolina Department of Transportation (SCDOT) or the City of Charleston Department of Traffic and Transportation (T&T).
SCDOT provides guidance for traffic-calming devices on state-controlled roads through its Traffic Calming Guidelines. On roads not controlled by SCDOT, the local municipality establishes the requirements for installation.
Charleston’s traffic-calming program
In 1999, T&T developed the Neighborhood Traffic Calming Program to improve safety and quality of life for residents and, in some cases, help restore the residential character of neighborhoods.
The program’s benchmarks include:
- The street must be residential, with at least 90% of properties zoned residential and a speed limit of 25 mph or less.
- A petition must be signed by 75% of residents in the project area. After receiving the petition, T&T conducts a speed and volume study to verify the need.
- After the study, T&T submits the request to the Charleston City Council Traffic and Transportation Committee for approval.
- Following City Council approval, T&T finalizes the device location and installation timeline.
- After installation, T&T conducts a follow-up evaluation of the project.
Bringing the fire department into the review process
By 2022, the Charleston Fire Department had begun looking for a more formal way to monitor and evaluate the growing number of requests for speed humps because of concerns about their impact on response times.
A review of the 2018 South Carolina Fire Code, based on the International Fire Code with state amendments, identified a path forward through Section 503.4.1, Traffic Calming Devices. That section requires traffic-calming devices to be approved by the fire code official.
The Charleston Fire Department Fire Marshal’s Office (FMO) created a Traffic Calming Information Bulletin outlining the potential impact of the devices on emergency services, expectations for installation and the plan-review process. The bulletin also references the existing SCDOT Traffic Calming Guidelines and T&T program standards.
Once the program was established, the city began collecting more detailed information about existing traffic-calming devices and analyzing how they affected emergency response.
Mapping existing devices
City GIS staff built a mobile Esri Field Maps application to collect the locations of existing traffic-calming devices. Members of the FMO used mobile devices to verify locations, document attributes such as the type of speed hump and add previously unmapped devices.
The city also created a permitting process within its EnerGov software system to outline and track each step of the plan review, verify the need for a traffic-calming device and permit the installation. The review involves the FMO, T&T and the City GIS Department.
Measuring the response-time impact
During the FMO review, staff use the city’s GIS system to identify existing traffic-calming devices along an intended response route, calculate the effect of existing and proposed devices and verify compliance with installation requirements.
The FMO assessment includes:
- Applying a 10-second response-time delay for each traffic-calming device.
- Verifying that traffic-calming devices do not increase response time by more than 1 minute cumulatively and that travel time to the farthest protected structure along the response route does not exceed 5 minutes.
- Limiting devices to roadways with posted speed limits of 25 mph or less.
- Avoiding streets that serve as primary or routine emergency response routes, including departure routes from fire stations. The Institute of Transportation Engineers defines these routes as streets commonly used by emergency vehicles because they allow faster travel, provide access to adjacent areas and have fewer physical impediments.
- Avoiding streets that serve as primary access routes to multiple residential streets or highly populated areas.
- Generally maintaining at least 350 feet between a device and an intersection and 350 feet between individual devices.
Turning GIS data into a planning tool
Once new traffic-calming devices are approved and installed, their locations are added to the city’s GIS database. Through ArcGIS Online maps and dashboards, the GIS team can provide the FMO and T&T with device locations, response-time impacts and other statistics.
Charleston currently has about 634 traffic-calming devices, the majority of which are parabolic speed humps.
The city has evaluated all addresses using GIS network-routing analysis to determine how those devices affect emergency travel times, including the number of speed humps along a route and the additional travel time from the closest fire station.
Proposed speed humps are also added to the response-time model, allowing reviewers to assess their potential impact before approving a request. Note: Some devices installed before the 2022 permitting process are on routes where travel times exceed the city’s current requirements.
The GIS data can also be shared with other systems, including First Due and the department’s mobile data terminals, giving first responders additional information about their response routes.
The data can also be viewed in table form for further analysis.
Balancing neighborhood safety and emergency access
Traffic-calming devices will likely remain a popular way to address speeding on existing roads and may become increasingly common in the design of new developments. For the fire service, the challenge is ensuring that each installation improves neighborhood safety without creating an unacceptable effect on emergency response. Continued assessment will be essential to ensure traffic-calming measures do not unintentionally extend emergency response times or compromise the safety of the community.
ABOUT THE AUTHORS
Deputy Fire Marshal and Battalion Chief Rick Fluegge joined the Charleston Fire Department Fire Marshal’s Office (FMO) in 2010. His responsibilities include Fire Plan Review, Permitting, Inspections, and Investigations. He currently serves as the FMO’s primary representative in the City of Charleston Permit Center, which provides a unified “one-stop” permit service to the public.
City GIS Developer Sandy Gagné has been with the City of Charleston since 2019. In this role she creates map-based solutions for all City departments, and her recent work includes a mobile app for collecting ADA parking space locations, online editing tools for tracking capital improvement projects, an affordable housing database and public dashboard, and response-time analyses and data collection for the traffic calming device program.
