Evaluating and communicating project impact is crucial. Before measurements, data collected before the implementation of a project, define the problem to be solved and the suitability of the proposed solution, as well as providing a baseline to demonstrate change over time. After measurements, data collected after implementation, ensure that the project has achieved the desired results and inform future adjustments to the project. Publicizing this data helps stakeholders understand the rationale and results of the project, and helps build public support.
Measurements are typically done three years before and after a road diet, although this can vary depending on the type of project. Not all measurements will be relevant to every project. Relevant measurements should be selected based on the context and goals identified, but here are some useful before and after measurements and a matrix for recording them that can help get you started.
Measure the number of motor vehicles, bicycles, and pedestrians throughout the day. Identify peak times, and calculate the total volume of daily users.
Find the annual rates of all collisions—motor vehicle crashes with injuries, bicycle injuries, pedestrian injuries, etc.—and add them together. Distinguish between injuries and serious injuries / death.
Calculate the average speed and the 85th percentile speed (a common measurement for determining the highest safe speed on a street), noting the speed limit of the street.
Measure point-to-point vehicle travel times between intersections, turn times at intersections, and pedestrian crossing times. Also take note of crosswalk times, and public transit operations and frequency.
Consider measuring traffic volumes, vehicle speeds, and other relevant measures on streets in the surrounding area to observe the impact of the road diet on traffic patterns nearby.
Compare parking utilization rates, turnover rates, and number of spots available to determine whether there is sufficient parking to meet demand and whether the redesign caused parking demand to increase.
Compare vacancy rates, rental rates, and sales values. Use surveys of residents, businesses, and visitors to evaluate additional economic impact. Another approach is examining the cost of vehicle collisions, road maintenance, and other traffic-related expenses compared to the cost of congestion (research has shown that the former is far more costly than the later).