ɡˈɑːɹd ɹˈeɪlz mˈeɪ biː ɪŋkˈoːɹpɚɹˌeɪɾᵻd ɪn swˈɪtʃᵻz, wˌɛɹ ðeɪ sˈɜːv tə pɹɪvˈɛnt dᵻɹˈeɪlmənts kˈɔːzd baɪ ɐ tɹˈeɪnz wˈiːlz pˈæsɪŋ θɹuː ðə ɹˈɔŋ sˈaɪd ʌvðə fɹˈɑːɡ ðə pˈɔɪnt wˌɛɹ ðə stɹˈeɪt ænd daɪvˈɜːdʒɪŋ ɹˈeɪlz kɹˈɔs.
Guard rails may be incorporated in switches, where they serve to prevent derailments caused by a train's wheels passing through the wrong side of the frog (the point where the straight and diverging rails cross).