Model sensitivity
To better understand the effects that changes in the variables within the model can have on the BCI value, an example is provided in table 10 and described below. A condition that is typical in an urban environment has been established as the baseline condition. This particular street segment is a two-lane road in a commercially developed area with a peak-hour volume of traffic in the curb lane equivalent to 250 vph. The lane widths are 3.4 m, and the 85th percentile speed of traffic along this segment is 56 km/h. Under these conditions, the BCI is 3.68. If this same street were in a residentially developed area, the BCI would be 3.42 or 7.2 percent less. If this street segment contained on-street parking, the BCI would be 4.19 or 13.8 percent greater. If the segment were a multilane street with comparable volumes in the lanes other than the curb lane, the index increases by just 1.6 percent to 3.74.
Changes or improvements to the baseline conditions of the roadway segment in terms of motor vehicle speeds, traffic volumes, and lane widths can also dramatically change the BCI. As shown in table 10, an increase in the lane width of 0.3 m decreases the index by 4.1 percent to 3.53. Similar reductions can be achieved by reducing the 85th percentile speeds by 8 km/h or the traffic volume by 100 vph. The most dramatic effect occurs with the addition of a 1.2-m bicycle lane to the existing facility; this change reduces the BCI value by almost 40 percent to 2.22.
