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Before-After Studies in Road Safety: Track Progress with Driving Data


  • What is a Before-and-After Study and what is it used for?
  • The Long Route to a Before-and-After Road Safety Study
  • Take the Short Route to a Before-and-After Road Safety Study, using Driving Data
  • MICHELIN DDi’s Expertise in Before-and-After Studies

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Undertaking a road safety project means validating the project, engaging a budget and organizing road work. A before-and-after study can provide valuable information about the safety reasons that lead to making the investment, and also whether the investment has been a success after implementation. Traditional studies require years of crash data, procedures for the analysis and complicated comparison sites. An alternative exists, however. A before-and-after study based on driving data gives road experts quantified and qualitative information about driving behavior and driving events. They compare like-with-like before and after safety treatments are introduced. With driving data, DOTs benefit from the (im)measurable value of key performance indicators that truly help to save lives.

What is a Before-and-After Study and what is it used for?

The Federal Highway Administration states that before-and-after studies

“are used to estimate crash effects associated with the implementation of a traffic safety measure.”

The field of study can be vast or highly precise. A before-and-after study can research and compare

  • the change in the annual number of crashes at a location
  • the change in the number of crashes at peak hours
  • the change in the crash rate per million vehicle miles traveled
  • the change in crash severity
  • the change in certain targeted crash types associated with the implemented road safety measure
  • sideswipes
  • left-turn related crashes
  • pedestrian- or bike-related crashes.

A before study gives an evaluation of road safety, and an after study provides information about what effect a given road safety intervention has had at a specific location. DOTs want to know if the effect is positive, and also if it can be reproduced at other locations.

The Long Route to a Before-and-After Road Safety Study

While before-and-after studies are valuable, getting the information they provide about road safety measures is not always easy. And the information may not lend itself readily to new sites where the same measures could be applied.

Challenges with Traditional Observational Before-and-After Studies in Road Safety

Time: A minimum of three years of crash data is recommended for any study. Before and sometimes after the road safety measure is implemented.

Cost: Undertaking a study this long requires a certain level of investment, that may simply not be feasible in some circumstances.

Analysis: It may be difficult to compare before and after results, and decisively judge whether the road safety treatment has had an impact. In some cases, fundamental questions can’t be answered, leading to a comparison site being chosen that shares similar features (type of street, location, types of road users, type of intersection, etc.). The comparison site data helps to remove any crashes that are not due to the implemented road safety measures from the results.

Results: In some instances, effects may be flagrant. In others, road experts and DOTs may not be able to draw precise conclusions about the effectiveness of the implemented measures.

Take the Short Route to a Before-and-After Road Safety Study, using Driving Data

With driving data, before-and-after road safety studies can become simple, perfectly intelligible and a valuable source of a road treatment’s effectiveness. The reasons to invest in a road treatment, and its impact, can come across clearly in quantified and qualitative information.

The Key Performance Indicators in Driving Data Before-and-After Studies

Time: In a few weeks’ time or less, driving events – sudden and atypical changes in driving behavior – can be identified at a given location. These include harsh acceleration, harsh braking, speeding, phone handling and suspected collisions. Safety measures are implemented to address the root cause that is provoking the driving behavior. In a matter of weeks, the driving data shows how driving behavior has been affected, and to what degree.

Cost: The budget depends on what driving data needs to be captured and how it will be analyzed. Before and after budgets can also be similar in scope, so that costs are predictable. In fact, before-and-after studies using driving data can be done in-house. Road management officials apply as and when needed.

Analysis: Driving data points are each based on an actual driving event. Data points are aggregated, to show general trends, and contextualized, to include time stamps and specific weather conditions. Compatible with a geographic information system, road experts visualize where driving events occur and their severity, and can decide on road safety measures. Once implemented, experts see the real impact of a road safety treatment on driver behavior, again in terms of numbers, severity and location.

Results: Road experts have facts on which to base decisions. They get real key performance indicators that clearly show what progress has been made. Comparing driving events before and after safety measures are adopted helps experts continue to adjust, iterate and reproduce the measures in new locations, saving lives proactively.

MICHELIN DDi’s Expertise in Before-and-After Studies

Adding driving data to before-and-after studies gives road management experts a clear view in a short space of time of managing safety problems on their transportation network, before and after safety measures are introduced.

MICHELIN DDi, Your Partner for Proactive Road Safety

Using the driving data provided by MICHELIN DDi, your road safety becomes proactive. Combining our expertise in data analysis and driving behavior, we create solutions that help you identify, locate and evaluate where road safety issues are happening in your road system.

We collect driving events in our driving data. After aggregating and contextualizing them, we apply machine learning, mathematical models and our own algorithms to deliver insights for safer roads. You receive data that is compatible with GIS systems, which helps in locating risky road zones and analyzing why they are risky.

For before-and-after studies, you receive information that is measured within a timespan of months and makes for easy comparison, showing your real progress in proactive road safety almost instantly.

Choose from a level of service that is tailored to your needs:

  • Level 1: Locate where and count how often driving events happen
  • Level 2: Assess and rank near miss hotspots
  • Level 3: Identify the probability of a crash happening.

You have real key performance indicators with our driving data and driving events. You are able to evaluate and prioritize road safety measures for all of your risky road zones – before car crashes happen. Once changes have been implemented, driving data KPIs again show the impact of the changes made.

Partner with Michelin DDi to accelerate your road safety strategy. Reach your Vision Zero goals with our mobility insights.

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