Metro completes traffic study on likely future bus pathway

Demolition of the Alaskan Way Viaduct is planned for 2017 and will require bus service to move to a new, permanent pathway to and from downtown Seattle.

Having determined that a two-way pathway on Columbia Street seems best for riders, we’ve talked with stakeholders along this pathway who would be affected by this change. Their input helped us design a traffic study to analyze different street configurations that would allow buses to travel in both directions on Columbia street between First and Third avenues.

The results of this study are in. Here’s a brief summary:

We studied three options for converting Columbia Street to two-way operation between First and Third avenues in downtown Seattle. The study assumed 40 buses per hour in the peak direction (into downtown Seattle in the morning and leaving downtown in the evening). Each of the three options includes conversion of one westbound general-purpose lane to an eastbound transit lane.

Option 1

This option maintains a three-lane configuration between Third Avenue and Alaskan Way. It has one general-purpose lane for through movement and left turns, and transit lanes in both directions. Right turns are allowed from the westbound transit lane. The eastbound transit lane allows local access for general-purpose traffic between First and Second avenues. This traffic would then be forced to turn right at Second Avenue.

What we learned:
This option provides a shared through/left turn lane at Second Avenue, causing left-turning vehicles to block through-traveling vehicles and increasing traffic delays, queues, and travel times. It could provide wider sidewalks (4-5 extra feet on each side) between First and Third avenues given that it has one fewer lane than options 2 and 2a.

Options 2 and 2B

Option 2 has four lanes: a transit lane in each direction and two general-purpose westbound lanes.  From Second to Third Avenue, the two general-purposes lanes allow through-movement of traffic and left turns to Second Avenue.  From Second to First Avenue, the two general-purpose lanes allow a through/left turn movement onto First Avenue and a right-turn-only lane onto First Avenue.  Right turns are allowed from the westbound transit lane. The eastbound transit lane allows local access for general-purpose traffic between First and Second avenues. This traffic would then be forced to turn right at Second Avenue.

What we learned:
Option 2 allows for an exclusive left-turn lane at Second Avenue, resulting in faster travel times, less delay, and less vehicle queuing than Option 1 for general-purpose traffic. It does not provide for wider sidewalks from First to Third Avenue because of its a four-lane configuration.

Option 2B is the same as Option 2, except that general-purpose vehicles can’t use the eastbound transit lane for local access.

Conclusion

Because of the impacts to general-purpose traffic in Options 1 and 2B, the study’s recommendation is that Option 2 is the best configuration for a two-way Columbia Street.

The information from this study will inform our work with the City of Seattle and stakeholders as we begin designing a future two-way pathway for transit on Columbia Street.

• Read the Columbia Street Traffic Study Executive Summary
• Read the Columbia Street Traffic Study Full Report