Self-enforcing roadways bringing safety up to speed

Over the past decade, speeding has contributed to about one-third of the more than 11,000 fatalities on roadways in Illinois, according to the Illinois Department of Transportation.

Seeking to increase roadway safety are Illinois Center for Transportation and IDOT in a joint project, “R27-SP71: Advancing Self-Enforcing Streets Phase 1: The Relationship between Roadway Environment and Crash Severity.”

Alireza Talebpour, University of Illinois Urbana-Champaign professor, led the effort with Stephane Seck-Birhame, IDOT Bureau Chief of Safety Programs and Engineering, and Victoria Barrett, Chicago Metropolitan Agency for Planning senior transportation planner.

The three aimed to improve understanding of self-enforcing roadways, which use visual cues and physical layouts to control speeds, as well as identify opportunities and barriers to their use in Illinois.

“Rather than design to allow the highest possible speeds safely, self-enforcing or self-explaining roadways use geometry and design features to constrain speeds to what is believed to be safe for the context,” Barrett said.

Features of self-enforcing roadways include speed feedback signs, narrower or reduced number of travel lanes, speed humps, and curves or shifts in the roadway, among others.

The researchers examined national and international studies on self-enforcing streets and conducted a preliminary analysis of the impacts of roadway elements on crash severity in Illinois.

Talebpour’s team examined data from over 1.15 million crashes in Illinois between 2019 and 2022 and used Google Street View to obtain geospatial data from those sites, with the goal of developing a methodology for analyzing relationships between roadway geometry and features and crash outcomes.

They applied image segmentation — an AI technique that trains computers to interpret images by classifying pixels into specific categories — to determine trends in crash severity and contributing factors.

From the segmentation results, they developed multinomial logit models, which predict probabilities based on multiple possible outcomes, to explore how roadway features impact crash severity.

The models found a relationship between crash severity and road and vegetation characteristics.

“Higher percentages of visible road surface were strongly linked to more severe crashes, with fatal crashes becoming more likely as road surface increased,” Talebpour said. “Severe crashes were more common in darker conditions and during weekends.”

“These findings highlight the need for designs that better manage driver perception and behavior,” he added.

The next steps involve studying additional landscaping and roadway elements and their influence on speeding as well as identifying cost-effective ways to modify road designs.

IDOT aims to use the findings to develop preliminary guidance for self-enforcing roadways, where appropriate.

“Road safety is IDOT’s highest priority,” Seck-Birhame said. “The general public will benefit from road designs that nudge them in obeying traffic laws, notably speed limits. IDOT will benefit from another design tool in our effort against speeding.”