sentences:  (For example, the undivided two-lane highway connecting Mexico City and Puebla is MX 150 , whereas the six-lane toll expressway is MX 150D).Mexico has had difficulty in building an integrated highway network due to the country's orography and landscape characteristics—most of the country is crossed by high-altitude ranges of mountains.Over the last two decades, Mexico has made impressive investments in order to improve its road infrastructure and connect main cities and towns across the country.