Crash maps, GIS and countermeasure tools: how analysts pick road fixes that work
How agencies turn map patterns into road fixes and what evidence to ask for
Safety Behind the Wheel Foundation built this guide from Federal Highway Administration (FHWA) safety guidance and the national traffic control device standard, National Highway Traffic Safety Administration (NHTSA) guides, Insurance Institute for Highway Safety (IIHS) data and published countermeasure research. Every source is listed at the end.
What crash mapping and countermeasure tools do
Traffic collisions took 39,254 lives in the United States in 2024 [1]. Behind each number is a place, and many places share the same warning signs. Crash mapping and countermeasure tools help agencies see those patterns and choose fixes. Treat the map as the start of a question, not the answer.
A few terms help. Crash mapping means plotting crash records on a map. A geographic information system, or GIS, is software that stacks layers of data, such as collisions, roads and schools, on one map. A countermeasure is any change meant to prevent collisions or lessen injuries. It can be a road feature, a rule or a program.
Four jobs come up again and again: find patterns, explain them, pick a fix and check the result. FHWA’s Proven Safety Countermeasures list gathers fixes shown to reduce deaths and serious injuries [2]. Its search page lets you answer a few questions about a location and get a tailored list of options [2].
Public roads belong to a city, county or state. The national standard for traffic control devices on any street open to public travel is the Manual on Uniform Traffic Control Devices, or MUTCD [3]. Where the manual calls for a decision, an engineer makes it using judgment or a study [3]. Residents, schools and employers should never add signs, markings or barriers on their own.
This article explains the tools so you can follow the analysis and ask better questions. To learn how to read a public map, see our guide to local crash data and safety maps. To rank community priorities, see how to use local crash data. This article goes one step further, to how analysts turn patterns into fixes.
What a mapping tool holds
A useful tool holds more than dots. FHWA guidance says crash, roadway and traffic data should be linkable by location on one road basemap [4]. A basemap is the base road map that every other layer is pinned to. The guidance points to linear referencing for this job, which fixes each record to a measured spot along a road [4]. It also says states with a full basemap should place all collisions on it, starting with fatal and serious injury collisions [4].
Comparison compiled by Safety Behind the Wheel Foundation
Data layers in a mapping tool
| Data layer | What it adds | Common weak spot |
|---|---|---|
| Crash records | Where, when, crash type and injury level | Late entries and wrong locations |
| Roadway features | Lanes, speed limit, curves, intersection type | Often missing on local roads |
| Traffic volume | Exposure, meaning how many vehicles or walkers use the place | Counts may be old or absent |
| Context layers | School routes, transit stops, lighting, hospitals | Layers come from different agencies and years |
Roadway data matters because raw counts mislead. FHWA’s Model Inventory of Roadway Elements is a list of roadway and traffic data items built to support data driven safety decisions [5]. With those items, an agency can compare a site’s crash history with the average number expected for roads with similar features and traffic [5]. A busy four lane road should have more collisions than a quiet lane. The real question is whether this place has more than similar places.
Check the data before you trust the picture
Analysts audit the data before they study the map. FHWA guidance names six traits to improve in safety data: timeliness, accuracy, completeness, uniformity, integration and accessibility [4]. In plain words, ask whether the data are recent, placed correctly, filled in, coded the same way, linkable to other data and open to you.
One source rarely tells the full story. Police, hospital and ambulance records each capture different parts of a collision, so ask whether the tool links them. If a map shows mostly property damage, ask which injuries may be missing from the police file.
Severity and exposure need the same care. Severity means how badly people were hurt. A map that blends every injury level and ignores traffic can send money to the busiest road instead of the riskiest one.
Which analysis answers which question
Tools answer different questions, so analysts often use more than one. Hot spot analysis ranks single locations by crash history. Predictive analysis uses roadway and traffic data to estimate how many collisions a site should have. Systemic analysis puts low cost to moderate cost fixes where the risk of severe collisions is greatest [6].
The Highway Safety Manual, published by AASHTO, is the recognized source of methods for measuring safety on existing or proposed roads [7]. It includes predictive methods and CMFs [7].
Comparison compiled by Safety Behind the Wheel Foundation
Three analysis approaches and their limits
| Approach | Question it answers | Main limit |
|---|---|---|
| Hot spot (site) analysis | Which places had the most or worst collisions? | Small counts swing from year to year |
| Predictive analysis | Does this place have more collisions than similar roads should? | Needs roadway and traffic data plus trained staff |
| Systemic analysis | Which places share the features behind severe collisions? | Needs a clear target crash type |
FHWA states that the systemic approach does not replace site analysis. Both are needed in a full safety program [8]. Rural roads show why. Severe collisions there make up a large share of all severe collisions, but they are thinly spread, so no single spot stands out [8].
Research backs the risk feature idea. A 2020 study built a ranking for 89 urban intersections in Orange County, Florida, using road safety inspections. Its ranking agreed closely with statistical crash estimates, with a rank correlation of 0.93 for total collisions [9].
Systemic analysis, step by step
FHWA’s Systemic Safety Project Selection Tool, published in 2013, lays out a planning process [8]. It defines a risk factor as a feature common to places where severe collisions occurred. Finding that feature at other places signals a chance of a future severe collision [8].
- Pick focus crash types and risk factors. Review systemwide crash data, such as every severe collision in a county, and look for shared features [8].
- Screen and rank locations. Check individual curves, road segments and intersections against those risk factors [8].
- Select countermeasures. Build a short list of low cost, highly effective fixes [8].
- Prioritize projects. Put the candidates in order so work can be funded and built [8].
- Evaluate the program. Track results afterward. The tool includes high level direction for this step [8].
A real package shows the idea. FHWA describes a systemic approach for stop controlled intersections. It uses doubled up oversized warning signs on both sides of the road, oversized Stop signs, brighter sign sheeting, better markings and cleared sight lines [10]. FHWA lists a 10 percent drop in fatal and injury collisions at all locations and a 15 percent drop in nighttime collisions [10]. At rural intersections, fatal and injury collisions fell 27 percent [10]. FHWA reports an average benefit cost ratio of 12 to 1 on a cautious three year service life [10].
Drivers may meet these signs at intersections with no recent collision, because systemic work targets shared risk features [6, 8]. Treat oversized warning signs as a cue to slow early and check both ways.
How to read a crash modification factor
A CMF is a multiplier. It estimates how a change shifts collisions of one type. A CMF below 1.0 points to fewer such collisions, and the gap from 1.0 shows the size of the drop. A CMF of 0.80, for example, means one fifth fewer. A CMF above 1.0 points to more. FHWA’s page on the stop controlled package lists the ID numbers of the CMFs behind its figures and links to the CMF Clearinghouse [10]. Start from the ID, then read the underlying study before using the number.
Comparison compiled by Safety Behind the Wheel Foundation
How to read a crash modification factor value
| CMF value | What it suggests | Question to ask |
|---|---|---|
| 0.90 | About 10 percent fewer collisions of the type studied | Which crash type and which road type? |
| 0.50 | About half as many | Was it tested on roads like ours? |
| 1.00 | No clear change | Was the study too small to tell? |
| Above 1.0 | More collisions of that type | Which road users were hurt? |
A fix does not work the same way for every crash type. A 2026 study of 17 formerly uncontrolled suburban intersections in Guangdong Province, China, found that adding signals raised total collisions. The CMF was 1.884 [11]. Rear end, same direction sideswipe and nonmotorized user collisions rose, while fatal and angle collisions showed no significant change [11]. The authors point to supporting measures, such as left turn control, pedestrian and nonmotorized user facilities, and approach channelization [11].
Context also moves the number. A 2026 study of color guidance markings on exit ramps of South Korean motorways, which are freeway type roads, compared busier and quieter ramps [12]. Collisions fell 47.5 percent where traffic was below 20,000 vehicles per lane per day [12]. Where traffic was higher, the drop was 31.0 percent [12]. For fatal and serious injury collisions, the drops were 74.4 and 54.7 percent [12].
The authors add that their method cannot fully account for regression to the mean, so results need confirming [12]. That term means places picked after an unusually bad stretch often improve even with no fix.
Guides for people focused fixes
Not every fix is concrete and steel. NHTSA’s Countermeasures That Work is a reference guide meant to help State Highway Safety Offices select effective, science based countermeasures for highway safety problems [13]. Its chapters cover alcohol impaired driving, speeding, seat belts, distracted driving, pedestrians, young drivers and more [13].
The chapters are organized by problem, not by place. So the map comes first. Ask which problem a cluster points to, then weigh an engineering fix and a behavior fix side by side. The same evidence questions apply to both. Who tested it, where, and with what result?
Match the tool to your role
Many public tools are free. Commercial analysis software and consulting firms exist too. Before any purchase, ask what data the tool needs, who keeps it current, whether its methods follow the Highway Safety Manual [7] and what training comes with it. Driving schools and defensive driving courses teach personal habits, not place analysis. For analysis training, ask your state transportation department or regional planning agency. FHWA’s local road safety plan site also lists guides and training [14].
Comparison compiled by Safety Behind the Wheel Foundation
Where to start, by role
| Who you are | Tool or step to start with | Watch for |
|---|---|---|
| Parent or resident | Public crash dashboards and your state’s crash map | A few dots on a quiet street may reflect little traffic |
| School or district | NHTSA’s free spreadsheet tool for planning bus stops and routes [15] | Speed, traffic volume, visibility and walking paths [15] |
| Fleet or employer | Map your own collisions and near misses by location | Small counts; share patterns with the road owner |
| Nonprofit or coalition | Pool public data and report by corridor | Check claims against official data |
| Road agency or local official | Local road safety plan, systemic screening, CMF review | Staff time, data gaps and upkeep |
NHTSA says its tool serves school and transportation officials who review current stops, respond to parents who ask for a stop review, or plan new stops [15]. Related NHTSA guidance advises keeping students off high speed roads, generally those above 35 mph, as walking routes or crossings [15]. It also urges discretion when asking for signs, since a crowd of signs fades into the background [15]. Safety Behind the Wheel Foundation gives residents and schools the same advice.
Limits, upkeep and common mistakes
Every tool has limits. These mistakes show up most often:
- Chasing a one year spike instead of a multiyear pattern.
- Treating a CMF as a promise rather than an average from other places.
- Mapping collisions with no traffic or walking counts.
- Skipping a field visit, where sight lines, driveways and driver behavior show up.
- Adding signs until none stand out [15].
- Never checking whether the fix worked.
Local engineering conditions decide whether a fix fits. Speed limits, sight lines, lane layout, driveways and utilities can all change what is possible. That is why a documented engineering study matters. The MUTCD defines one as an analysis and evaluation of available information, and it must be written down [3].
Upkeep matters as much as the first analysis. Refresh the data at least once a year. Keep a log of filters and changes, such as a new road or a closed driveway. After a fix, compare the site with similar untreated sites, because chance swings can mimic success [12]. Tools also change, so check the date on any guide before relying on it.
Ask your road agency for an analysis
FHWA’s local road safety plan framework has four steps: identify stakeholders, use safety data, choose proven solutions and put them in place [14]. FHWA’s page reports lower death or severe crash totals in places that used such plans, with examples from Minnesota, Washington State and Thurston County, Washington [14].
Put your own request in writing. Name the road, the crash type, the time of day and what you see. Then follow up.
Frequently asked questions
Is a crash map the same as a GIS?
A crash map is one output. A GIS is the software and data system behind it. It can stack crash records with roads, traffic counts, school routes and lighting. Analysts use that stack to test ideas, such as whether collisions cluster on roads with the same curve or intersection type. The map you see online is often a simple view of that larger system.
Is a hot spot list enough to pick fixes?
Usually not. FHWA says the systemic approach does not replace site analysis, and both are needed [8]. A hot spot list can show where collisions piled up, but it can miss spread out risk on rural roads [8]. It also says little about which crash type to target or which fix fits.
Where do crash modification factors come from?
They come from studies that compare collisions before and after a change, often with untreated sites as a comparison [11, 12]. The Highway Safety Manual includes CMFs [7]. FHWA’s stop controlled intersection page lists CMF ID numbers behind its figures [10]. Study design matters, and results can differ by traffic level and crash type [11, 12].
Can a small town or school district do this work?
Yes, in steps. Start with free public data and FHWA’s local road safety plan framework [14]. School officials can use NHTSA’s free stop planning tool [15]. Ask your state transportation department or regional planning agency whether they can run the analysis or share data. Small crash counts mean local staff should lean on risk features, not counts alone.
Why did a fix not cut collisions at my street?
Several reasons are common. The fix may target a different crash type than the one that occurs there. Traffic levels may differ from the studies behind the CMF [12]. Some crash types can rise while others do not change [11]. Small numbers also swing by chance. Ask the agency to compare against similar untreated sites.
Can residents install signs or markings?
No. The road owner selects, designs and installs devices on public roads, guided by the national standard [3]. Unapproved signs can confuse drivers and may add risk. NHTSA also warns that a crowd of signs fades into the background [15]. Instead, send the agency a written request with specific facts, and ask how the location will be reviewed.
The bottom line
Recommendation from Safety Behind the Wheel Foundation
Safety Behind the Wheel Foundation encourages residents and local leaders to ask what data and evidence stand behind every proposed road fix. Crash maps and countermeasure tools work best as a chain. Good data feed a map. The map shows patterns. Analysis explains the pattern, and a matched fix follows. A later check shows whether it worked.
You do not need to run the software. You can ask which years and injury levels were used, whether traffic counts were included, which crash type is targeted and what evidence supports the fix. Those questions help agencies choose fixes that protect people on your roads.
Related articles
- Local crash data and safety maps: how to find and read your area's data
- How to use local crash data to choose community safety priorities
- Safe System approach: how road design protects you from human mistakes
- Safer road design: a field guide to the safety fixes on your street
- School bus and school zone safety: when to stop and how to protect kids
- Video near miss analysis: what traffic conflict studies show and what they cannot predict
Sources and further reading
- 1IIHS-HLDI. Fatality statistics. Page undated. Data year: 2024. iihs.org/research-areas/fatality-statistics
- 2Federal Highway Administration (FHWA). Proven Safety Countermeasures. Page undated; the search tool is at [https://highways.dot.gov/safety/proven-safety-countermeasures/search.](https://highways.dot.gov/safety/proven-safety-countermeasures/search.) highways.dot.gov/…/proven-safety-countermeasures
- 3FHWA. Manual on Uniform Traffic Control Devices for Streets and Highways, 11th Edition, Part 1 (General). December 2023 (FHWA lists a Revision 1 dated December 2025). mutcd.fhwa.dot.gov/pdfs/11th_Edition/part1.pdf
- 4FHWA Office of Safety. Guidance on State Safety Data Systems. Issued March 15, 2016. highways.dot.gov/media/10691
- 5FHWA. Model Inventory of Roadway Elements (MIRE). Page undated. highways.dot.gov/…/model-inventory-roadway-elements-mire
- 6FHWA. Systemic Approach to Safety. Page undated. highways.dot.gov/…/systemic
- 7FHWA. Highway Safety Manual (describes the manual published by AASHTO). Updated February 18, 2026. highways.dot.gov/…/highway-safety-manual
- 8FHWA Office of Safety. Systemic Safety Project Selection Tool. Published July 2013. highways.dot.gov/…/sspst.pdf
- 9Montella A, Guida C, Mosca J, Lee J, Abdel-Aty M. Systemic approach to improve safety of urban unsignalized intersections: Development and validation of a Safety Index. Accident Analysis and Prevention. 2020;141:105523. Data year: crash data from 89 Orange County, Florida intersections (years not stated in abstract). [https://pubmed.ncbi.nlm.nih.gov/32251742/](https://pubmed.ncbi.nlm.nih.gov/32251742/) (DOI [https://doi.org/10.1016/j.aap.2020.105523](https://doi.org/10.1016/j.aap.2020.105523)) doi.org/10.1016/j.aap.2020.105523
- 10FHWA. Systemic Application of Multiple Low-Cost Countermeasures at Stop-Controlled Intersections (FHWA-SA-21-031). Page undated. Data year: based on studies published in 2017, per FHWA. highways.dot.gov/…/systemic-application-multiple-low-cost…
- 11Dai B, Wang X, Guo Q, Yue L, Luo G, Bai Y. Safety effects of signalizing uncontrolled intersections on suburban arterials: An empirical Bayes before-after evaluation by crash type. Accident Analysis and Prevention. 2026;237:108737. Data year: 2020 to 2025. [https://pubmed.ncbi.nlm.nih.gov/42679516/](https://pubmed.ncbi.nlm.nih.gov/42679516/) (DOI [https://doi.org/10.1016/j.aap.2026.108737](https://doi.org/10.1016/j.aap.2026.108737)) doi.org/10.1016/j.aap.2026.108737
- 12Han S, Lim JS. The estimation of crash modification factors of Color Guidance Markings near exit ramps in motorways using the Comparison Group method. Traffic Injury Prevention. 2026. Data year: not stated in abstract (South Korean motorways). [https://pubmed.ncbi.nlm.nih.gov/42605752/](https://pubmed.ncbi.nlm.nih.gov/42605752/) (DOI [https://doi.org/10.1080/15389588.2026.2709734](https://doi.org/10.1080/15389588.2026.2709734)) doi.org/10.1080/15389588.2026.2709734
- 13National Highway Traffic Safety Administration (NHTSA). Countermeasures That Work. Page undated. nhtsa.gov/…/countermeasures-that-work
- 14FHWA. Local Road Safety Plans. Page undated. Data year: not stated on page. highways.dot.gov/…/local-road-safety-plans
- 15NHTSA. Planning Safer School Bus Stops and Routes and “Planning for Safety” toolkit pages. Tool created 2022; pages undated. [https://www.nhtsa.gov/planning-safer-school-bus-stops-and-routes](https://www.nhtsa.gov/planning-safer-school-bus-stops-and-routes) and nhtsa.gov/…/planning-safety
This article reflects the safety priorities of careful road safety analysis and choosing proven fixes for local roads. It is general education, not legal, engineering, insurance or financial advice. Tools and guidance change, so verify details with official sources. For a specific road, contact the city, county or state agency that owns it. For school stops, contact your district's transportation office. Questions about a collision you were in belong with your own insurer or attorney. Reviewed October 2026.
Cite this article: Safety Behind the Wheel Foundation. “Crash maps, GIS and countermeasure tools: how analysts pick road fixes that work.” drivewithcare.org, https://drivewithcare.org/crash-mapping-gis-countermeasure-selection-tools/. Reviewed October 2026.
Special thanks to our contributors
We appreciate the professionals, experts, and community members who share their knowledge and perspectives to help make this resource better. Your insights are always welcome and appreciated.
Have professional expertise, firsthand experience, or a perspective that could make this resource better?
We welcome your input. Your knowledge and experience can help us make this resource more useful, accurate, and meaningful to the people who rely on it.
Thank you. Your contribution is on its way.
We’re grateful you took the time to share your knowledge with us. Our team reviews every contribution with care. If it helps improve this resource, we’ll update the page and recognize you the way you chose.
Keep learning
Safe Driving Resource Center
Guides, self-checks and articles for drivers, parents of new drivers, and families recovering after a crash.
