In 2019 the City of Seattle opened a local freight and transit (FAT) lane to explore ways to address the challenges of freight mobility. This study evaluated the performance and utilization of the FAT lane.
As the demand for goods and services increases in Seattle, the Seattle Department of Transportation (SDOT), under the scope of its Freight Master Plan, is attempting to develop solutions to address the challenges of freight mobility. To investigate one potential approach, in January 2019, upon the closing of the Alaskan Way Viaduct, SDOT allocated the curbside lane on S Alaskan Way between S Jackson St and S King St (running north to south) to transit buses and freight vehicles.
The SDOT engaged the Supply Chain Transportation and Logistics Center at the University of Washington to evaluate the performance and utilization of the FAT lane. Street camera video recordings from two separate intersection locations provided data. Researchers used the videos to count vehicles and categorize them into ten different groups, including drayage vehicles with a container and drayage vehicles without a container, to capture their different behavior.
Analysis of traffic volumes showed that transit buses chose the FAT lane at the two locations over 96 percent of the time, and authorizing freight vehicles to use the lane did not affect that lane choice.
Bicycle riders also chose to use the FAT lane more than other vehicles, with a usage rate of between 81 and 95 percent at the two locations.
The truck percentage at the two FAT lane locations peaked at 3:00 pm, at just over 35 percent. Transit bus volumes peaked at 5:00 pm, and with increasing numbers of buses in the FAT lane, truck volumes decreased.
Congestion led to higher violation rates in the FAT lane. In congested traffic, the percentage of all vehicles in the FAT lane increased by between 37 and 42.5 percent for the two locations. However, instead of higher rates of trucks, more unauthorized vehicles, such as work vans and other vehicles, used the FAT lane.
Quantitative analysis showed that the time of day, location, day of week, and vehicle type influenced lane choice. For all vehicle types, the probability of choosing the FAT lane was higher during the morning and afternoon hours, and on Wednesdays, Thursdays, and Fridays.
Qualitative observations showed that many drivers were confused by the FAT lane. Freight companies could be notified beforehand so that the drivers would know about the location and functionality of the lane. For future projects, clearer signage and information should also be provided for drivers.
The city will be able to use these research findings on the FAT lane’s performance to guide the development of future FAT lane projects.
Author: Anne V. Goodchild, UW Department of Civil and Environmental Engineering
Sponsor: Seattle Department of Transportation