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Abstract
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Highest Scoring Abstract: Doctoral
Background
In 2017, Michigan raised the speed limit from 70 to 75 mph for passenger vehicles on 614 miles of freeways and raised the truck speed limit from 60 to 65 mph on all freeways statewide. While most of the focus of this policy change has focused on weighing the cost of safety and fuel consumption with the benefit of reduced travel times, little attention has been paid to the impact this policy will have on air pollution and human health.
Methods
Speed data were collected using LIDAR speed detectors from a vehicle not readily visible to motorists. At each site, it was attempted to collect 100 readings for passenger vehicles and 10 readings for trucks in each direction, alongside volume counts. Before data consisted of 85 sites (59 study sites and 26 control sites); after data were collected for 42 sites (19 control sites and 23 increase sites). Average speed data were weighted by volume, which was used to estimate fuel economy of vehicles. Exposure data was then used to estimate the increase in fuel consumption and literature values were used to estimate the impacts to human health and air pollution.
Results
A t-test demonstrated that there was a significant increase (p<0.0001) in passenger car speeds on study segments, while speeds on control segments did not change (p=0.997). Speeds for trucks, however, significantly increased for both control and study segments (p<0.0001), which is to be expected, as the speed limit for trucks increased statewide. Passenger car speeds increased from an average of 72.0 to 74.0 mph while truck speeds increased from 61.1 to 62.7 mph along study corridors and from 61.0 to 62.5 mph along control corridors. Passenger car fuel economy did not change along control corridors and declined from 24.2 to 23.4 mpgUS along study corridors. Truck fuel economy declined from 6.4 to 6.2 mpgUS statewide. Ultimately, it was estimated that CO emissions will increase by 1,490 tonsUS, NOx by 213 tonsUS, PM2.5 by 3.32 tonsUS, and CO2 by 77,100 tonsUS annually. The greatest concern for human health is PM2.5, with costs to human health of $88,000-$130,000/metric ton.
Conclusions
Operating speeds increased for passenger cars along study corridors, and truck operating speeds increased statewide after freeway speed limits increased. This resulted in fuel economy declining, and consequently, emissions increasing. The increase in PM2.5 emissions is the most concerning emissions increase due to the large cost to human health.
Language: en |