The Marmaray Project consisted of an improvement to the suburban rail system in Istanbul., connecting the stations of Halkali (on the European side) and Gebze (on the Asian side) with a total of 76.3 Km in length, and including construction of a rail tunnel under the Istanbul Strait (or Bosphorus). Contract CR3 centred on collaboration in the Site Technical Office for design of the necessary electrical substations to power the new rail system, including review of designs, calculation of structures and design of mechanical installations, sewerage, drainage and oil catchments.