Sources in the literature vary widely in their recommendations for maximum cul-de-sac length, but the reasons given for the various dimensions (such as minimizing inconvenience to delivery people) are not convincing. The general wisdom, however, suggests some limits on cul-de-sac lengths. As the street gets longer, properties accessible from only one direction become more isolated and difficult to reach. Moreover, the cul-de-sac ceases to be a street that provides access to a few properties and instead assumes the function of a higher-order street (subcollector or collector). To reap the benefits of cul-de-sacs - such as reduced traffic in residential areas, the opportunity to downscale the size of the street, and the opportunity to create more intimate neighborhoods - communities must limit the number of vehicles using the street.
In general, traffic, volume and the number of housing units should be the factors that determine cul-de-sac length. A street with houses on 100-foot-wide lots can function well for a greater length than a street with 50-foot lots. For 100-foot-wide house lots, a street of 20 houses would result in a 1,000-foot-long street. For 50-foot-wide house lots, a cul-de-sac should be restricted to a length of approximately 500 feet. Assuming that a cul-de-sac should handle no more than 200 vehicle-trips per day and that each single-family home generates up to eight or 10 vehicle-trips per day, a cul-de-sac should accommodate a maximum of 20 to 25 houses. In some circumstances, including large lots or difficult terrain, lengths longer than 1,000 feet might be appropriate.
[From Residential Streets, Second Edition, American Society of Civil Engineers, National Association of Homebuilders and the Urban Land Institute, 1990, pages 54 & 55]
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