The governing body of each municipality in this state may provide for and regulate crosswalks, curbs and gutters. However, after September 28, 1975, all new curbs which are constructed in any municipality, and all existing curbs which are a part of any reconstruction, shall comply with this section. In order to enable persons using wheelchairs to travel freely and without assistance, at each crosswalk a ramp shall be built into the curb so that the sidewalk and street blend to a common level. Such ramp shall be not less than thirty-six inches wide and shall not have a slope greater than one inch rise per twelve inches length (eight and three-tenths percent). Where because of surrounding buildings or other restrictions it is impossible to conform the slope with this requirement, the ramp shall contain a slope with as shallow a rise as possible under the circumstances not to exceed ten percent. In all ramps there shall be a gradual rounding at the bottom of the slope.