Simulating the Impact of Traffic Calming Strategies

Chimba, Deo; Mbuya, Christian · 2019 · ROSA P / Western Michigan University. Transportation Research Center for Livable Communities

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Summary

This study assesses the operational impacts of traffic calming measures on speed, travel time, and roadway capacity in residential and urban environments. Motivated by the need to evaluate these measures for livable communities without relying solely on costly field experiments, the research utilizes microsimulation to analyze physical calming devices—specifically speed tables, speed humps, and raised crosswalks—as well as the influence of bus stops on road diets. The methodology involved data collection from roadway segments in the Metro Nashville area, including traffic counts and GPS trajectory data from moving test vehicles to establish speed profiles at one-second intervals. The researchers developed and calibrated a microscopic simulation model using PTV VISSIM software. A multi-regime model was employed to fit steady-state equations, establishing speed-flow relationships for various calming scenarios. The study also evaluated the impact of bus stops on road diets by modeling transit operations with varying dwell times and using Surrogate Safety Assessment Model (SSAM) measures to analyze safety conflicts. Key findings indicate that traffic calming features significantly reduce vehicle speeds but also decrease roadway capacity. Capacities for residential segments with calming features ranged from 640 to 730 vehicles per hour (vph). The spacing of devices critically influenced this reduction: spacing speed tables 1050 feet apart caused a 23% capacity reduction, while 350-foot spacing reduced capacity by 32%. Similarly, speed humps spaced 350 feet apart reduced capacity by 33%, compared to a 30% reduction at 700-foot spacing. The analysis revealed a linear decrease in capacity of approximately 20–37 vph per lane depending on spacing. Speed tables were found to be slightly superior to speed humps in preserving roadway capacity. To achieve desirable crossing speeds of 15 mph or less, particularly near schools, a spacing of 630 feet or less is recommended. Regarding road diets, bus stops with dwell times of 10, 20, and 30 seconds caused speed reductions of 9.5%, 12%, and 20%, respectively, at a flow of 300 veh/hr. Bus bays caused an approximate 8% speed reduction at higher flows (1400 vph). Conflict analysis showed that the location of curbside bus stops significantly affected the number of rear-end and crossing conflicts. The study concludes that while traffic calming effectively reduces speeds, it imposes a measurable penalty on roadway capacity that varies with device type and spacing. Speed tables offer a better balance between speed reduction and capacity preservation than speed humps. Furthermore, the integration of bus stops into road diets requires careful consideration of dwell times and stop locations to mitigate speed reductions and safety conflicts. These findings provide engineers with evidence-based guidelines for designing traffic calming schemes that balance safety, livability, and operational efficiency.

Key finding

Speed tables preserve roadway capacity slightly better than speed humps, and spacing calming features at 630 feet or less is required to achieve desired crossing speeds of 15 mph or lower.

Methodology

simulator

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• speed management
• perceptual countermeasures
• traffic density

Information type

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• Empirical Findings: crash risk outcomes