 The mostly aluminium alloy body gives light weight to help acceleration and energy efficiency.Electrostar units have a shorter version of the Turbostar's body as Electrostars have 3 or 4 cars per unit rather than 2 or 3 for Turbostars.Class 357 units were built with capability, although the maximum line speed on the London, Tilbury and Southend Railway (the "Essex Thameside" franchise) is at present only .