pɚhˈæps hɪz mˈoʊst nˈoʊɾəbəl ɐtʃˈiːvmənts wɜː ðə mˈeɪdə hˈɪl ænd ˈɪslɪŋtən tˈʌnəlz ðə lˈæɾɚ wʌzðə lˈɔŋɡɪst ɔnðə kənˈæl, ænd wɛn tˈɛlfɚd hɪmsˈɛlf wʌz ɪnvˈaɪɾᵻd tʊ ɪnspˈɛkt ɪɾ ɪn wˈʌn θˈaʊzənd ˈeɪthˈʌndɹɪd ˈeɪtiːn, hiː oʊpˈaɪnd: "mətˈɪɹiəlz ænd wˈɜːkmənʃˌɪp ˈɛksələnt, ænd ɪts dᵻɹˈɛkʃən pˈɜːfɛktli stɹˈeɪt".
Perhaps his most notable achievements were the Maida Hill and Islington tunnels – the latter was the longest on the canal, and when Telford himself was invited to inspect it in 1818, he opined: "materials and workmanship excellent, and its direction perfectly straight".