Istanbul registered a 17 percent drop in its traffic index values over the last three years, a metropolitan municipality report has revealed.

For Turkey's most populous city, with more than 15 million inhabitants, the index shows the amount of time lost in traffic. Previously, the city's notorious traffic was alternately named the worst or second worst in the world by navigation device manufacturers.

The report by municipality's transportation department shows that the index at 35 percent in the morning rush hour in 2015 decreased to 31 percent this year while for evening rush hour it came down to 48 percent from 58 in 2015. Experts have credited the improvement to a series of new routes, including the Eurasia Tunnel and Yavuz Sultan Selim Bridge, opened in 2016. Both have helped bring down travel times in two main routes, the D-100 and TEM highways straddling the city's European and Asian sides divided by the Bosporus waterway.

Eurasia Tunnel links Kazlıçeşme on the European side with Göztepe on the Asian side and is city's only underwater tunnel for cars. The two-story tunnel reduces the travel time in busy hours from 100 minutes to only 15 minutes. On the other hand, Yavuz Sultan Selim is the third bridge over Bosporus. It looks to relieve the Istanbul traffic from the impact of trucks and other heavy vehicles as authorities directed truck traffic to the eight-lane bridge north of the city.

Diverting truck traffic to third bridge relieved the burden on the Fatih Sultan Mehmet Bridge and the July 15 Martyrs' Bridge on Bosporus, according to the Istanbul Metropolitan Municipality. The same report noted a 12 percent drop in vehicular traffic on these two bridges in 2017.

The report focuses on busy routes such as the one between Kozyatağı district and the Atatürk airport. It would take about two hours to cover the route in evening rush hour in 2015 which has gone down to just 49 minutes this year.

Istanbul is home to more than 4 million vehicles and an expanding network of mass transit. Local officials strive to promote more use of mass transit, especially the exclusive-lane bus service Metrobus and the subway.