The world's longest road tunnel under construction in Turkey reaches a major milestone this week, with the world's first road-rail hybrid tunnel officially launched for tolling on Tuesday. Tunnel operator Cengiz-Yildirim Group reports that first passengers crossed the 10.5-mile (16.3 km) route in a shuttle bus and that traffic is now flowing through the world's longest single tunnel. The tunnel was opened to commercial traffic on April 24. It is the first of its kind anywhere in the world, according to reports. Cengiz Yildirim Group The complex project was developed jointly by Cengiz-Yildirim Group and Kolin-Yildirim (Kolin-Yildirim Aslan Savunma Sanayi ve Ticaret ve Ticaret A.S.) and will carry 18 million people a year. The Tünel is located 1,935 meters (6,370 feet) under the Bosphorus Bridge and was designed to transport passengers, vehicles, cargo and pedestrians without any interruption. A world first Kolin-Yildirim's Hakan Yildirim says that with the successful opening of the tunnel, it has become the first tunnel of its kind anywhere in the world. The project was developed by Cengiz-Yildirim Group and Kolin-Yildirim, Yildirim said. The company says the construction of the road-rail tunnel project is part of a wider plan for Istanbul's road, transport and urban development to address issues in a city that has a population of 14.5 million people. Yildirim says the company is proud that the project has become a world first. Related: The most expensive tunnel in history was just completed in China Transit system without a railway? A spokesman for Cengiz-Yildirim, Yusuf Polat, tells CNN that the tunnel will have a total of nine stations on the western and eastern ends of the tunnel. The tunnel has an annual capacity of 180,000 cars, 1 million passengers, and 18,000 motorbikes. In addition to Istanbul's rapid transport system, the tunnel has a capacity to accommodate 2.5 million passengers annually. With three exits on the Bosphorus Bridge and three on the Fatih Sultan Mehmet Bridge (one of which is for pedestrians), the road-rail tunnel will save residents up to 45 minutes in their commute time, according to a press release by the project operator. Yusuf Polat The rail component of the Tünel is the first step in implementing the Istanbul mass rapid transport system (MART), which will allow for trains to travel at high speeds in both directions. The Tünel will include a tunnel-based MART line as well as a railway, a new airport rail connection and a funicular line over the hills. Yusuf Polat says the tunnel can be used by cargo and trains to bypass Istanbul's narrow streets. Istanbul's urban congestion Turkish President Recep Tayyip Erdogan called the opening of the road-rail tunnel "a historic day for Istanbul." But Erdogan also warned that the Tünel would not be an end-all solution for Istanbul's public transportation needs and that "there is a big need for a railway in Istanbul." The rapid transport system, once in place, will help reduce congestion and improve traffic conditions on Istanbul's streets, according to Erdogan. Erdogan is scheduled to host a summit on Istanbul's urbanization challenges on Tuesday. The Tünel will be available for use at 7 a.m. for free on weekdays for six months. Related: The most expensive tunnel ever built cost $9 billion Related: Here are the world's 10 longest tunnels Are we ready for this? The tunnel's opening in a major European city comes amid a trend toward urbanization and urban transformation. Many of Istanbul's major road-rail tunnels were built during the 1980s and 1990s, including two tunnels near the city of Edirne in northeastern Turkey. The Tünel project required two shafts at a depth of 150 meters (490 feet), the installation of four train lines with 11 stations and the building of two elevated railways. The tunnel's construction included some challenges. A section of the road-rail tunnel experienced unexpected geological conditions and needed repair. The tunnel is 975 meters (3,228 feet) wide, with 18 exits on the Bosphorus Bridge and seven on the Fatih Sultan Mehmet Bridge. The tunnel's longest underground road section was 14.5 miles (23.7 km), while the longest tunnel section below ground is 1.2 miles (2.0 km). The tunnel will be equipped with a tunnel ventilation system that meets OHS standards and a lighting system, including a high-tech lighting system. -- Jethro Mullen and Aakriti Thapar contributed reporting to this article.