Accessible public transportation facilitates participation in social and recreational activities. The slope of the ramps on public transportation vehicles affects accessibility of these vehicles. The changes in these ramp slopes proposed by the United States Access Board are perceived to be too steep by people with disabilities. The purpose of this study was to evaluate perceived usability of different ramp slopes in public buses. Experimental apparatus with a ramp and height adjustable platform was constructed at the University at Buffalo. Twenty seven participants in the age group of 18-85 years who are manual wheelchair users, power wheelchair users, and people with visual impairment were recruited. Perceived difficulty, acceptability, and exertion were assessed using subjective rating scales. Statistical analysis using two-way ANOVA and ordinal regression showed that 1:4 and 1:6 slopes were difficult whereas 1:8 and 1:12 were acceptable by most of the participants. These results can impact the design policies for public transportation vehicles.