During Wednesday’s meeting of the West Seattle Bridge Community Task Force (WSB coverage here), a member asked why motorcycles aren’t allowed to use the low bridge at all times. SDOT’s Heather Marx said traffic engineers had recommended against it, calling it a safety issue, and promised to provide the inquiring member with the detailed explanation. We subsequently requested it, since many WSB readers have asked, and received it today:
While a motorcycle is physically smaller than a car, they still require roughly the same amount of room on all sides to travel safely. This is because a large truck or bus needs just as much room to stop safely when they are following a motorcycle as they do for any other kind of vehicle. While two motorcycles could theoretically travel side by side, most motorcycles would likely be travelling on their own and occupy and entire lane.
This means that from a traffic engineering perspective, motorcycles take up essentially the same amount of room as a car. This is especially true at traffic signals or in stop-and-go conditions where congestion is created by the cumulative reaction time of every individual driver waiting to go forward after the vehicle in front of them moves ahead. In this situation, the number of vehicles in a line of traffic is just as important as the size of each individual vehicle, and so motorcycles could be expected to add to congestion at the Chelan 5-way intersection just like cars do.
We also have safety concerns about motorcycles travelling next to large trucks and buses in stop-and-go conditions, especially because congestion would likely increase considerably if more motorcycles took this route.
If you have a question about that – or any other bridge issue – note that SDOT will be part of both community meetings we’ve previewed for tonight, the Town Hall at 6 pm and West Seattle Transportation Coalition at 6:30 pm.