Not enough parking, you say? A study of garage use and parking supply for single-family homes in Sacramento and implications for ADUs

Accessory dwelling units (ADUs) are increasingly touted as part of the solution to the intransigent housing shortages facing many metropolitan areas across the United States. But numerous barriers to ADU development persist, including opposition by neighboring households. One persistent question is whether ADU residents would overwhelm on-street parking in the predominately single-family neighborhoods where ADUs are typically built. That question is difficult to answer because there is a surprising dearth of research on the effective parking supply in single-family neighborhoods. We use a survey of homeowners in Sacramento, California, to investigate the supply and sufficiency of residential parking for single-family homes, including how households actually use their garages, and help answer the ADU parking conundrum. After estimating and accounting for actual garage use, we find that more than 75% of households have enough off-street parking available to park all their vehicles. When we combine off-street and on-street parking supplies, we find that households have an average of 1.6 more parking spaces available to them than they have vehicles. That parking surplus is more than enough to accommodate the average ADU tenant and their vehicle, belying claims that ADUs will overwhelm existing parking supplies in single-family neighborhoods.