Good point. There must be a turnout which connects TKO with TRT via by-pass line. There are 2 express trains (one weekly & other bi-weekly) running in CGL - CJ - AJJ section. So if they want to provide electric loco for these trains from Nagercoil/Madurai to Wadi, then they have to run these trains via new line, then loco reversal will be required at Arakkonam Junction. To avoid this loco reversal they might have provided a turnout (as some trains skip Arakkonam Junction). Please try to observe whether there this turnout or not next time when you are traveling to Bengaluru