The third track from Zagreb to Karlovac: 'We will continue to have similar problems'

The construction of a third lane along the highway connecting Zagreb to Karlovac has officially entered its planning phase, marking a significant step in Croatia's infrastructure development. The project involves building a 39-kilometer stretch of motorway between Zagreb and Karlovac, estimated to cost around 250 million euros. According to Tomislav Mihotić, the state secretary at the Ministry of Sea, Transport, and Infrastructure, public consultations have already begun, and following these discussions, formal procedures for a public tender will commence. If everything proceeds as planned, the third lane could be operational by 2029. However, during the construction period, existing lanes will be narrowed, and speed limits will be reduced, although both directions of the highway will still maintain two lanes each. This temporary adjustment is expected to cause some disruption but is deemed necessary for the long-term improvement of traffic flow.

The need for this new lane arises from persistent congestion issues on the current route, particularly during summer months and extended weekends. Traffic jams frequently occur between Zagreb and Bosiljevo, highlighting the growing demand on the existing infrastructure. While the addition of a third lane is seen as essential due to the increasing volume of freight traffic, experts caution that it may not fully resolve the congestion problems. Dr. Marko Ševrović, an associate professor at the Faculty of Transportation Sciences in Zagreb, points out that while there will be some improvements, similar bottlenecks are likely to persist under comparable conditions. He warns that within a decade, the discussion might shift toward constructing a fourth lane if current trends continue.

One critical issue identified by Ševrović relates to the Drežnik overpass, which lacks a stopping lane and would require complete reconstruction to accommodate the new third lane. Similarly, the Saint Mark tunnel presents challenges that need addressing to ensure continuity of the new lane towards Bosiljevo. These structural limitations underscore the complexity of integrating the new lane into the existing network without causing further disruptions.

In addition to physical infrastructure upgrades, Ševrović emphasizes the importance of implementing section-based speed control measures. Current traffic congestion on the Zagreb-Lučko and Karlovac-Zagreb segments is attributed primarily to a speed limit of 130 kilometers per hour, which results in lower throughput efficiency when compared to speeds around 100 kilometers per hour. This discrepancy leads to sudden changes in traffic flow, known as shock waves, contributing to phantom traffic jams. Ševrović suggests reducing the speed limit to 80 kilometers per hour in such congested areas, a practice commonly adopted in Western countries. This approach could potentially increase capacity almost as effectively as adding another lane, according to him.

Support for this proposal comes from the Croatian Automobile Club, represented by Dr. Sinan Alispahić, who acknowledges the necessity of speed restrictions despite potential increases in travel times. He believes that patience and awareness regarding the broader implications for sustainable transportation systems will lead to widespread support for these measures. The club endorses the idea of section-based speed control, recognizing its potential benefits for improving overall traffic management.

As part of ongoing efforts to enhance traffic flow, the implementation of contactless toll collection systems is being introduced on the Lučko segment and other sections of the highway. These technological advancements aim to streamline operations and reduce delays, complementing the infrastructure developments aimed at alleviating congestion. With daily traffic volumes reaching up to 82,000 vehicles on the A1 highway alone, the urgency for comprehensive solutions becomes evident.

The integration of these various strategies—physical expansion of roadways, intelligent traffic management techniques, and modern toll collection methods—reflects a multifaceted approach to addressing Croatia’s growing transportation demands. As the country moves forward with these initiatives, continuous evaluation and adaptation will be crucial to ensuring their effectiveness in managing future traffic growth sustainably.