How can we measure the impact of carpool lanes on urban mobility?

The introduction of carpool lanes changes travel habits on major urban roads. For local authorities and operators, it is essential to understand the real impact of these developments on traffic, safety, and the environment in order to guide mobility decisions.
At Alyce, we develop methodologies to accurately assess these impacts, combining counting, behavioral analysis, and monitoring of environmental indicators.

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The main methods for measuring the impact of carpool lanes

Passenger counting

Monitoring vehicle traffic allows us to assess the actual use of carpooling and the effectiveness of carpool lanes. This counting is carried out in the Île-de-France region, in several regions via the National Road Safety Observatory, and for shared lanes in Lyon. This type of measurement is made possible by automated AI camera counting. Other devices exist, but this technology allows for comprehensive coverage.

Analysis of carpool parking lots

Studying parking lot occupancy and usage allows infrastructure to be adapted and areas where accessibility can be improved to be identified. Image processing observations over varying periods of time provide detailed insight into user behavior in these specific parking areas.

This type of parking analysis is in high demand, as it provides an objective basis for planning decisions aimed at decarbonizing individual transportation and shifting toward public transportation. Alyce has analyzed the use of carpool parking lots in the Lyon metropolitan area (France), for example, providing useful indicators for measuring the impact of this mobility and planning policy.

Behavioral studies and flow monitoring

The AI-based minUi tool analyzes road behavior with a view to establishing a dedicated lane. Analyzing merging over several kilometers, traffic jams, lane changes, traffic, and speed are quite complex measurements to produce without this tool. The information collected provides reliable indicators of how users are adopting carpool lanes.

Monitoring of safety and environmental indicators

Comprehensive observation of traffic composition, congestion, speed, and potentially dangerous behavior can also be useful in studies of the impact of noise pollution or pollution.

Additional measures relevant to evaluating a carpool lane

To gain a comprehensive overview of the indicators to be monitored, it may be useful to supplement the counting and flow data with:

• Accessibility and connectivity: monitoring connections from secondary roads and public transport links, in particular using adjusted FCD data and origin-destination surveys conducted through interviews.

• User satisfaction: surveys or questionnaires to measure users’ perceptions of carpooling and dedicated lanes. These surveys can be conducted in the field, via carpooling operators, or via email/internet/social media campaigns.

• Socio-economic impact: analysis of infrastructure costs, time savings for users, and more generally, assessment of the project’s externalities.
• Additional environmental indicators: monitoring of CO₂ emissions, fine particles, noise pollution, and specific pollutants depending on location.
• Spatial and temporal analysis of traffic flows: mapping of congestion zones and variations according to peak hours or days of the week, via analysis of data from permanent sensors or FCD data.

These measurements and assessments provide a comprehensive view of the effectiveness and real impact of a carpool lane, beyond simple traffic counting or analysis.

A concrete example: the Paris ring road in 2025

After introducing a dedicated carpool lane on the Paris ring road in 2025, the assessment carried out, combining carpool lanes and a speed limit of 50 km/h (Source: APUR study on monitoring developments on the Boulevard Périphérique), shows:

• Overall traffic: down 4 to 7% depending on the period.

• Traffic jams: -14% over 9 months, up to -36% on carpool lane during peak hours.

• Speed: -8% during the day, -18% at night, but +8.2 km/h on the dedicated lane

• Accidents: down 14% over 9 months, down 31% in July-August.

• Noise level: -2 to -2.7 dB(A)

These figures reflect a trend toward calmer traffic on the ring road, with less congestion, less noise, and fewer accidents. Occasional effects related to weather or roadworks do not reverse this positive trend.

The evaluation of a dedicated carpool lane is based on a combination of several types of data: passenger counts, behavioral analysis, safety, environment, and additional measures such as user satisfaction and economic impact.

This information provides a better understanding of the actual effects of developments and supports the planning of more effective mobility policies tailored to users’ needs.

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