This research examined the safety and operational effects of roadway lane width on mid-block segments between signalized intersections as well as on signalized intersection approaches in the urban environments of Lincoln and Omaha, Nebraska. In the safety analysis, the Poisson and negative binomial regressions with fixed or random parameters were estimated to evaluate the effects of lane width on annual crash frequencies at mid-block segments and intersection approaches. In the operational analysis, linear regressions were used to examine lane width effects on the vehicles’ speed at mid-block segments. The Kolmogorov-Smirnov test was applied to explore the effects of lane width on the vehicles’ headways in the queue on the intersection approaches. At the mid-block segments in comparison with 11 ft and 12 ft wide lanes, 10 ft lanes on the higher speed limit (40 mph and 45 mph) roadways had ambiguous impacts on safety, with improvements in some locations and reduction in the others. Lanes 11 ft or 12 ft wide were found to be safer than 10 ft lanes on lower speed limit roadways (roadways located outside of the central business district with a 35 mph speed limit). On intersection approaches, the combination of narrowed left-turn lanes and narrowed through lanes was a safer option based on the evidence uncovered in this research.