An understanding of the relationship between lane width and traffic operations is important in making decisions about urban and suburban arterials. Numerous geometric elements, including lane width, affect the saturation flow rate at an intersection on an urban or suburban arterial. Several studies have been conducted to evaluate the relationship between lane width and saturation flow rate at intersections. This relationship is investigated on urban and suburban signalized intersection approaches by using field-study sites with the most ideal conditions possible. Research results indicate that saturation flow rate varies with lane width. Average saturation flow rate was in the range of 1,736 to 1,752 passenger cars (pc)/h/ln for 2.9-m (9.5-ft) lanes, 1,815 to 1,830 pc/h/ln for 3.3- to 3.6-m (11- to 12-ft) lanes, and 1,898 to 1,913 pc/h/ln for lane widths of 4.0 m (13 ft) or greater. These measured saturation flow rates are generally lower than those currently used in the Highway Capacity Manual (HCM). Furthermore, the percentage difference in saturation flow rate between sites with 2.9- and 3.6-m (9.5- and 12-ft) lanes was about half the value used in the HCM. Because data were limited to queue lengths between 8 and 11 vehicles, the research results do not directly address queue lengths longer than 11 vehicles.