What Is Traffic Calming?

Traffic calming measures like road diets, speed bumps, and even street art help improve road safety by reducing vehicle speeds and inducing less risky driving. Mobility data helps determine which measures are needed where, clearing the path toward political and public buy-in.

As the U.S. road safety crisis worsens and pedestrian deaths spike, encouraging slower, more attentive driving — i.e., calming traffic — is critical to saving lives. To do this, planners and engineers turn to a variety of traffic calming measures that reduce traffic speeds and keep drivers’ attention on the road and their fellow road users.

Budget issues were on everyone’s mind at our October StreetLight Summit. Hundreds of StreetLight InSight® “power users” from DOTs, MPOs, consulting firms, and other organizations met online to discuss 2020’s rapid changes for transportation, and how to navigate them.

The biggest budget-related takeaways were:

1. When actual construction is up in the air, double down on planning.
2. Capture project-critical O-D details without commissioning surveys.
3. With budgets shrinking, get more value from existing resources.

Here are specific examples collected from panels and discussions that illustrate how shrewd practitioners are using Big Data analytics to support these budget-related best practices. 

1. With Spending On Hold, Planning Continues

At a time when many projects are in limbo, transportation professionals told us they are ramping up on planning. That way, when budgets are settled and projects begin again, planners will be confident they’ve analyzed and prioritized the most important work. 

Goals of Traffic Calming

The primary goal of traffic calming is to increase road safety by reducing vehicle speeds. Vehicle speeds are among the biggest factors impacting road safety, especially for those outside of vehicles. In fact, pedestrians are five times more likely to die from crashes when cars are traveling 40 mph vs. 20 mph, according to data from the AAA Foundation.¹

And with pedestrian traffic deaths up over 80% since 2009, calming traffic is a growing concern across the U.S. and other regions that have prioritized car-centric development. In fact, pedestrian deaths have soared, even as pedestrian activity (and therefore pedestrian exposure) has plummeted, signaling the need for urgent interventions to improve road safety.

And pedestrians aren’t the only Vulnerable Roads Users (VRU) impacted by high vehicle speeds. According to the Insurance Institute for Highway Safety (IIHS), cycling deaths have increased 55% since 2010,² and could increase further as post-pandemic cycling activity grows in many U.S. metros and states, unless safe cycling infrastructure is prioritized.

In some cases, traffic calming efforts may also seek to reduce vehicle throughput, which can in turn help reduce crash risk for all road users (fewer vehicles means fewer crashes). In fact, infrastructure and policy changes that reduce speed often have the side effect of reducing vehicle throughput, since road capacity and traffic speeds are linked. For this reason, proposed traffic calming measures often have to contend with concerns over increased congestion and lengthened commute times. However, analyses have shown that reduced vehicle throughput doesn’t have to lead to increased congestion, especially when planners are equipped with the right data.

A roadway in Banten, Indonesia combines multiple traffic calming measures — roundabout design, traffic cones, street art, and road texture changes.

Top Traffic Calming Measures

There are many factors that lead to high vehicle speeds, and just as many traffic calming measures to address them. These can include policy changes such as reduced speed limits as well as infrastructure changes like lane reductions and speed bumps.

One powerful traffic calming tool is the road diet. Road diets reduce the number of vehicle lanes on a roadway and typically repurpose the space for other infrastructure like bi-directional turns lanes, bike lanes, or pedestrian islands. By reducing overall vehicle capacity along specific corridors, road diets often reduce average travel speeds along these corridors as well, as drivers have less room to speed up or pass other vehicles.

When a road diet includes the addition of non-car infrastructure like protected bike lanes, bus lanes, and pedestrian islands, this can further improve road safety for those both in and outside of vehicles.

Photo source: Virginia DOT, reprinted in the U.S. DOT’s Road Diet Informational Guide

Similarly, traffic calming measures often have significant overlap with Complete Streets tactics, such as signalized pedestrian crossings and improved road signage, which help ensure that streets cater to all road users across all ages, abilities, ethnicities, and modes — not just those inside of vehicles.

Sometimes temporary traffic calming measures may be used to slow down traffic around road workers or special events, or to test the impact of traffic calming before investing in more permanent infrastructure. For example, traffic cones, jersey barriers, or portable pylons may be used to temporarily close lanes of traffic or install temporary traffic circles.

Other traffic calming measures include:

A painted crosswalk along with temporary pylons and traffic cones help calm traffic and protect cyclists on Armour Road in North Kansas City, Missouri.

Mobility Metrics for Traffic Calming Projects

To ensure the effectiveness of traffic calming measures and secure funding and political buy-in for proposed projects, transportation professionals often gather data on existing roadway conditions such as speed, vehicle volumes, and pedestrian activity.

Traditional Data Collection Methods and Online Mobility Data

While traditional data collection methods like roadway counters, manual counts, and surveys may be used, online mobility data can speed up data collection without putting staff in harm’s way or introducing bias or sample size issues common with surveys. Online mobility data is particularly useful when conducting before-and-after studies to evaluate the effectiveness of past traffic calming measures, because it allows analysts to go “back in time” and compare historical data to current conditions.

Planners can also use online mobility data to identify traffic patterns on roadways throughout an area and anticipate the impact of traffic calming measures on surrounding neighborhoods. These types of analyses can help assuage constituent concerns over traffic flow and gain buy-in on proposed traffic calming projects.

StreetLight’s Safety Prioritize tool helps planners and operations managers diagnose safety concerns and identify the best countermeasures based on the most up-to-date mobility data.

Key Metrics for Traffic Calming

Vehicle speed — or trip speed — is a critical metric planners and engineers use to identify where traffic calming measures may be needed and whether past traffic calming projects were effective.

Volume metrics like Annual Average Daily Traffic (AADT) can also help evaluate whether a corridor is a good candidate for traffic calming, and how reduced travel speeds may impact vehicle throughput.

Measuring pedestrian and bicycle activity along a corridor can also help determine where VRU exposure is high, indicating where traffic calming measures could be most urgently needed.

Traffic signal timing often plays a key role in intersection safety and regulating traffic flow. Turning Movement Counts can help pinpoint intersections that may benefit from signal retiming.

To ensure that traffic calming measures don’t lead to increased congestion, metrics such as Vehicle Hours of Delay (VHD) and Vehicle Miles Traveled (VMT) may also be analyzed. Our Congestion Solutions Guide explains how these and other metrics can be used to identify congestion solutions besides adding lanes, which can lead to dangerous traffic speed increases and even worsen congestion.

To learn more about the data behind effective traffic calming and other safety improvements, download our Transportation Safety Data Handbook.

Examples of Successful Traffic Calming

After the COVID pandemic reduced the number of vehicles on the road, instances of speeding rose significantly, leading to dangerous conditions on many roadways. To understand what was happening and address unsafe speeds, many communities implemented traffic calming measures.

One such community was the City of Pasadena, which saw a 60% decrease in traffic volumes and a 40% increase in instances of speeding after Stay at Home orders in 2020. The video below shows how they evaluated roadway conditions before and after traffic calming measures and drove down speeding by 25%.

While the pandemic highlighted an urgent need for traffic calming measures, traffic calming projects have a long history of success prior to 2020. For example, in 2019, Armour Road in North Kansas City, Missouri underwent a series of improvements, including the addition of a new protected bike lane and pedestrian refuges. A before-and-after study by StreetLight shows a significant reduction in dangerous vehicle speeds, double the biking activity, and a negligible increase in travel times (around five seconds on average) along the corridor.

Traffic calming projects like these prove that reducing dangerous traffic speeds doesn’t have to come at the cost of increased congestion. To learn how you can use online traffic data to justify traffic calming measures and gain public and political buy-in, check out our Safety Solutions page.

1. AAA Foundation for Traffic Safety. “Impact Speed and a Pedestrian’s Risk of Severe Injury or Death.” September 2011.

2. Insurance Institute for Highway Safety. “Fatality Facts 2021: Bicyclists.” May 2023.