On the exposure to mobile phone radiation in trains
  This report presents theoretical estimates of the Power Density levels which may be reached inside trains. Two possible sources of high levels of radiation are discussed. The first one arises since the walls of the wagons are metallic and therefore bounce back almost all radiation impinging on them. The second is due to the simultaneous emission of a seemingly large number of nearby telephones. The theoretical study presented here shows that Power Densities stay at values below reference levels always. 
J. Ferrer, L. Fernandez-Seivane, J. M. Hernando, M. B. Castan, L.   Garcia, and J. M. Vazquez