Assessment of physical activity needs to improve in order to gain a more comprehensive understanding of the relationship between characteristics of the environment and physical activity. Our study evaluated a method [Block Walk Method (BWM)] for observing physical activity along residential sidewalks and streets. The BWM was utilized in 12 U.S. Census block groups over a three-month period. Examination transportation routes (ETRs), 1,524 m in length, were constructed and examined in each block group. On 6 days, ETRs were traversed by a trained observer for 50 min. Physical activities, street names, and geographical locations (e.g., addresses) were recorded. We found encouraging results for the BWM. The level of agreement between independent observers was >98% for activity type. The number of individuals seen walking, running, or biking did not differ significantly between the days of the week or observation times. The number of individuals observed was correlated with block group characteristics (e.g., percent walking/biking to work) and weather (e.g., temperature). The BWM is an easy to use, economically viable observational approach to obtaining reliable information concerning physical activities performed on residential streets and sidewalks. Its use could help advance our understanding about the environment–physical activity relationship.