a drone to carry out survey work for the MTHL. The drones were fitted with 360 degrees camera that provide up to 3 millimeter accuracy. The aerial survey takes less time than a regular survey, achieves greater accuracy and helps protect against false claims for compensation. Over 1,000 boreholes were drilled to study the strata. The MMRDA began conducting a geological survey for the project on 15 January 2018. The project work will affect 1,635 trees of which 753 will be cut and the remaining 882 will be replanted at other locations. Most of the trees are located at Sewri and Vakola. Construction The MTHL is 21.8 km long, including 16.5 km sea bridge and 5.5 km of viaducts on land on either end of the bridge. It is being be constructed in three sections. Construction of the bridge required the use of 165,000 tonnes of reinforcement steel, 96,250 tonnes of structural steel, and 830,000 cubic metres of concrete. The bridge will feature the first use of orthotropic decks in India. The special steel decks will enable the bridge to have longer spans than possible with regular girders. A total 70 orthotropic decks will be used on the bridge requiring about 96,250 tonnes of steel. The steel spans will make up 6.41 km of the bridge length, while the rest will use concrete. The MMRDA chose to use steel spans in these sections to eliminate the need to construct pillars to support the bridge which could hinder the movement of ships in the area. This 4 km section includes a 180 meter long steel span, which is the longest steel span in India. The shortest steel span on the MTHL is 110 meters long. The foundations for the MTHL will be 47 metres at its deepest points in order to support the weight of the bridge. An automated girder launching system was utilized to lay the bridge's foundation, marking the first time the system was used in India. The MMRDA stated that the construction work would generate 115,419 man-months of employment. Prime Minister Narendra Modi laid the foundation stone for the project on 24 December 2016. Construction of the MTHL began in April 2018 with engineers collecting soil samples for soil testing at each location where piers will be built in Nhava Sheva. MMRDA Metropolitan Commissioner R. A. Rajeev stated on 28 October 2018 that about 9% of the project