How CERTH Used TraceMark Flow to Measure the Real Impact of Thessaloniki's Flyover Project
Measuring the real-world impact of a major infrastructure project is notoriously difficult. Traditional traffic counts and sensors can tell you what's happening at a handful of fixed points, but they rarely give the complete, network-wide picture needed to understand how construction is actually reshaping travel across a city. That was the challenge facing the Hellenic Institute of Transport, part of Greece's Centre for Research and Technology (CERTH), as it set out to measure the impact of Thessaloniki's ring road Flyover project, and it's a great example of TraceMark Flow and Google's Roads Management Insights working together in the field.
A major upgrade to a critical corridor
Thessaloniki's ring road has been undergoing a significant upgrade: an elevated motorway roughly 13.5 kilometres long, with four lanes in each direction, three new tunnels and ten elevated bridges. The goal is to ease congestion on the existing ring road and improve access to key destinations around the city, including the airport and popular holiday routes.
Projects at this scale bring years of construction-related disruption before the benefits show up. For CERTH, understanding that disruption before, during and after construction was essential to managing it well and keeping the public informed.
Why real-time, comprehensive data mattered
CERTH is one of Europe's leading research organisations, with its Hellenic Institute of Transport focused on traffic analytics, data fusion, AI-based traffic prediction, road safety and connected vehicle services. To do that work at the level Thessaloniki's Flyover project demanded, CERTH needed data that went well beyond what conventional sensors and traffic counts could offer.
That's where TraceMark Flow came in, powered by Google's Roads Management Insights and the broader Google Maps Platform. It gave CERTH's researchers real-time and predictive views of speed, trip duration and network performance, he kind of comprehensive, timely traffic intelligence that's difficult to assemble from traditional infrastructure alone.
What the data showed
Using TraceMark Flow, CERTH was able to measure the Flyover project's impact with real precision: travel times increased by 40 to 50% in both directions during construction, compared with the period before works began, while road accident numbers dropped significantly under the new traffic conditions. That combination gave CERTH's team a clear, evidence-based picture of the trade-off construction was creating, and the confidence to communicate realistic travel expectations to residents and commuters.
Beyond the headline numbers, TraceMark Flow gave CERTH much stronger situational awareness across the network, not just on the ring road itself, but on major arterial roads elsewhere in the city that were absorbing displaced traffic.
From measurement to management
The benefits didn't stop at monitoring. TraceMark Flow's short-term traffic forecasting helped CERTH identify emerging congestion and bottlenecks as they formed, and supported the search for reliable alternative routes for travellers navigating the city during construction. As Dr. Evangelos Mitsakis, Research Director at CERTH, put it, the access to high-quality real-time data ultimately improved decision-making across the city, helping traffic flows get redistributed and bottlenecks avoided.
A model for infrastructure projects everywhere
Thessaloniki's Flyover project is a useful case study for any agency weighing a major transport infrastructure upgrade. Before-and-after impact measurement is often treated as an afterthought, but CERTH's work shows what's possible when real-time, comprehensive traffic data is built into the process from the start turning a disruptive construction period into a well-managed, well-communicated one.
This post draws on a Q&A originally published on the Google Maps Platform blog, featuring Oliver Looker (NGIS) and Dr. Evangelos Mitsakis (CERTH).*