The barriers to physical mobility of the elderly are explained in this study which concentrated on spatial-temporal accessibility, and the use of mass transit to urban services and resources. The first area of concern dealt with the amount and extent of free time available to the elderly who are perceived as having large blocks of descretionary time available to pursue chosen activities. An attempt was made to determine if this discretionary time was affected by having to match schedules with the transit system. The second area of concern identified the constraints of physical capability, time, and authority on the elderly. To explore these questions, five mobile, elderly, female non-drivers from Denver and Boulder, Colorado, were selected to give accounts of their use of the mass transit system. Study participants identified several difficulties that impeded the productive use of their free time. An Examination of access to two senior citizen community centers revealed that the elderly participants could not join in many activities because of transportation problems. These non-drivers lacked flexibility in scheduling their leisure time, partially because of the constraints of the aging process, and partially because of the need to rely on a inflexible transportation system. (Author/APM)