The relationship between transit success and density is one that should be considered when planning transportation. Transit lines need to consider cost per passenger-mile in order to ensure financial feasibility. Some scholars suggest minimum density thresholds for successful transit of different types, but these rules do not always represent accurate ridership numbers. However, higher density in cities generally makes transit more feasible.

Key findings

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"They and other scholars found that rail transit, with its high up-front investment and high capacity, costs less than buses or cars only in corridors with high travel demand. Thus they found that rail was more cost-effective than buses or cars in high-density cities, while cars were more cost effective in low-density cities."

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"Transit-supportive density thresholds need to be viewed with caution. There is no one hard and fast rule that can be applied across all projects. Regression-based models mask considerable variation. For example, despite low surrounding densities, the Franconia Springfield extension of the Blue Line in Washington, DC, is one of the best performing investments. Low capital costs, a plentiful supply of parking at stations, frequent train service, and good access to downtown jobs contribute to low costs per rider."

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"Despite the unease many citizens, planners and politicians have with density, if costly rail and BRT investments are to pay off, larger shares of growth—particularly jobs—must be concentrated around transit stops. In addition to local land use policies, this will require a significant reorientation of transit funding priorities in favor of investments in areas that meet, or have credible plans to meet, minimum density thresholds."

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