However, low top speed is not always a differentiating characteristic between light rail and other systems. For example, the Siemens S70 LRVs used in the Houston METRORail and other North American LRT systems have a top speed of 106 kilometres per hour (66 mph) while the trains on the all-underground Montreal Metro can only reach a top speed of 72 kilometres per hour (45 mph). Los Angeles Metro light rail vehicles have higher top and average speeds than Montreal Metro or New York City Subway trains.  The main difference is that Montreal Metro and New York City Subway trains carry far more passengers than any North American LRT system, and the trains have faster acceleration, making station-to-station times relatively short in their densely populated urban areas. Most light rail systems serve less densely populated cities and suburbs where passenger traffic is not high, but low cost combined with high top speed may be important to compete with automobiles.