Methodology
Through research of peer MPOs and consultation with SEMCOG’s Transportation Safety Action Committee, Transportation Safety Task Force, Transportation Coordinating Council, and other regional stakeholders, SEMCOG developed regional targets for all five safety performance measures (found below) using a non-linear target setting methodology based on a similar approach from the Delaware Valley Regional Planning Commission (DVRPC).
With a non-linear approach, initial targets are more conservative then gradually increase the closer we get to 2050. This approach is more realistic than a linear reduction method, which assumes a consistent reduction year-over-year. This is due to the time required to implement policies and actions from the Southeast Michigan Transportation Safety Plan, as well as new technologies and advancements in vehicles. Once these actions are in place, the corresponding reductions in fatalities and serious injuries should increase over time. The following methodology was used for each target.
First, the baseline for each measure was determined using the average of the last five years of available data, 2017-2021. Data from the Fatalities Analysis Report System was used for fatality related measures. The State of Michigan crash database was used for serious injury related measures. Vehicle Miles Traveled (VMT) was calculated using data from the Highway Performance Monitoring System. This is consistent with federal guidelines for establishing baseline values.
Next, to keep initial future projections realistic and achievable, an initial reduction number for 2022 and 2023 was determined for each measure based on the annual change in five-year rolling averages from 2015 to 2019. Since we aspire to have reductions for each measure, only years with a reduction in the rolling average were considered. Crash data from 2020 and 2021 were excluded, as those years were highly influenced by the COVID-19 pandemic. SEMCOG’s future projections for travel demand and other forecasting currently exclude COVID data, so the same approach was used for safety target projections.
The median reduction number from 2015 to 2019 was selected as the projected 2022 and 2023 reduction number for each measure. In cases of an even number of years with reductions, the lower of the two middle numbers was used. Reduction numbers were rounded to the nearest whole number for fatalities and serious injuries. For rates, reduction numbers were rounded to the hundredths place. After the two initial reduction numbers were set, the annual reduction needed to be increased to reach zero by 2050. A consistent year-over-year percent increase in the reduction number was calculated for each performance measure, rounded to the nearest half of a percent. The following tables and charts show these values for each performance measure.