Toronto was planned out on a grid system of concession lines spaced about two kilometres apart that separated rural landholdings. Major avenues were established along each concession line as the city spread outward. These avenues run straight with few diversions for long stretches, and Toronto is notable for the considerable length of its major streets. Most of the avenues go from one side of the city to the other, and often continue deep into the neighbouring suburbs. Suburban expansion replaced these rural lots with subdivisions made of crescents and cul-de-sacs. These local road networks were designed to reduce and slow traffic, redirecting vehicles to the avenues. These wide avenues that even run through the central city have also made it easier for Toronto to retain a streetcar system, which was among the few North American cities to do so.