Characterization of Seattle’s Commercial Traffic Patterns: A Greater Downtown Area and Ballard/Interbay Vehicle Count and Evaluation

Seattle now ranks as the nation’s sixth-fastest growing city and is among the nation’s densest. As the city grows, so do truck volumes — volumes tied to economic growth for Seattle and the region as a whole. But many streets are already at capacity during peak hours and bottleneck conditions are worsening. This project is designed to deliver critical granular baseline data on commercial vehicle movement in two key areas of the city to help the city effectively and efficiently plan for growing freight demand.

This timely research from the Urban Freight Lab (UFL) on behalf of the Seattle Department of Transportation produces Seattle’s first complete estimate of Greater Downtown area traffic volumes. And it offers a detailed analysis of commercial vehicle traffic in and around one of the city’s two major industrial centers, the Ballard-Interbay Northern Manufacturing Industrial Center.

These efforts are significant because the city has lacked a comprehensive estimate of commercial vehicle volumes until now. In the Greater Downtown area, the cordon counts (tracking traffic in and out of 39 entry/exit points) alongside traffic volume estimates will provide a powerful tool for local government to model, evaluate, develop, and refine transportation planning policies. This study lays the groundwork for the first commercial vehicle traffic model that will enable the evaluation of different freight planning and traffic management strategies, economic growth scenarios, and application of new freight vehicle technologies. Ballard-Interbay is slated for major infrastructure projects in the coming years, including new Sound Transit stations and critical bridge replacements. This analysis will help inform these projects, which are critical to an efficient, reliable transportation system for goods and people.

One overall finding merits attention as it suggests the need to update some of the freight network element categories defined in the current Seattle Freight Master Plan. The SCTL research team finds that the volume of smaller commercial vehicles (such as pick-ups, vans, and step vans) is significant in both the Greater Downtown area and Ballard-Interbay, representing more than half of all commercial vehicles observed (54% in the Greater Downtown area and 60% in Ballard-Interbay.) Among those smaller commercial vehicles, it is service vehicles that constitute a significant share of commercial traffic (representing 30% in the Greater Downtown area and 40% in Ballard-Interbay.) Among the myriad possible ramifications of this finding is parking planning. An earlier SCTL research paper (1) found service vehicles tend to have longer dwell times, with 44% of all observed service vehicles parked for more than 30 minutes and 27% parked for an hour or more. Given this study’s finding of service vehicles representing a significant share of commercial traffic volume, these vehicles may have a disproportionate impact on parking space rates at the curb.

Comprehensive planning requires comprehensive data. Yet cities like Seattle often lack the detailed data needed for effective freight planning, from peak hours and fleet composition to activity type and gateways of entry/exit. And if cities do have data, they are often too highly aggregated to be useful for management or planning or suffer from lack of comparability or data confidentiality problems.

Currently, urban traffic volume estimates by Puget Sound agencies are limited in spatial and vehicular detail. For example:

• Seattle Department of Transportation (SDOT) is responsible for recording traffic counts through the year on selected arterial streets in Seattle, providing a seasonally adjusted average weekday total vehicle traffic for all lanes at all count locations.
• Washington Department of Transportation (WSDOT) provides annual average daily traffic volumes in select locations of their jurisdiction, including the major interstates and state highways in the Seattle area. This data includes truck volume separated into three types: single, double, and triple units.
• Puget Sound Regional Council (PSRC) regional truck model has three levels of vehicle classification: light commercial, medium trucks, and heavy trucks. This is based on WSDOT Annual Traffic Flow’s count locations and additional manual counts for model validation through the Puget Sound Region.

But none of these existing efforts produce enough detail to understand Seattle’s vehicle movements or connect them with economic activity. To fill the gap, Seattle could consider adopting a standard freight-data reporting system that would emphasize collecting and distributing richer and better data for time-series analysis and other freight forecasting, similar to systems used in cities like Toronto and London. Seattle is a national leader when it comes to freight master plans. This study offers a critical snapshot of the detailed data needed for effective policy and planning, potentially informing everything from road maintenance and traffic signals to electric vehicle charging station sites and possible proposals for congestion pricing. That said, Seattle could benefit greatly from sustained, ongoing detailed data reporting.