|Figure 1: Ross Island Bridge looking westbound|
The Ross Island Bridge is no stranger to vehicle congestion. Dubbed as one of Portland’s worst bottlenecks, the Ross Island Bridge connects over 51,000 commuters and four TriMet bus lines every day from Powell Boulevard to Downtown Portland . The mile-long bridge often snarls to a crawl during peak hour commute times, clogging the vital connection that links together East and West Portland over the Willamette River. The capacity issues with the Ross Island Bridge have rippled into other local transportation projects, including a planned Bus Rapid Transit (BRT) along Powell Boulevard, which runs into significant challenges when attempting to cross over the Ross Island Bridge or divert to another crossing .
What can be done? A bridge replacement or expansion on the Ross Island Bridge would be costly and followed by years of design and construction. A far better solution to provide immediate congestion relief at a fraction of the cost of bridge expansion is the use of flex lanes. Flex lanes, also known as managed lanes, allow for variable traffic directions by “borrowing” an extra lane for the high-flow direction during peak hour times . Flex lanes work by installing electronic overhead signage technology that can be changed during different times of the day to accommodate different traffic patterns along a roadway corridor. With the rising cost and environmental consequences of capacity-related expansion, many traffic engineers and transportation officials see flex lanes as an efficient solution to address roadway congestion . For the Ross Island Bridge, the addition of flex lanes means the four-lane bridge can operate as a six lane bridge (three lanes in one direction) for the peak direction.
Case Study: Taylorsville, Utah
Flex lane projects have been implemented across the United States. In 2012, the Utah Department of Transportation (UDOT) successfully installed flex lanes just south of Salt Lake City along Highway W 5400 S in the City of Taylorsville. The W 5400 S flex lanes, which run between Bangerter Highway and Redwood Road, control traffic flow for a 2.25 mile stretch of suburban highway . The $16 million dollar project comes at a fraction of the cost of equivalent roadway expansion would of been for capacity improvements, according the UDOT officials, with the added benefit of preserving property along the highway .
Under the current design shown in Figure 2, the W 5400 S flex lanes provide four eastbound lanes, a center turn lane and two westbound lanes during the morning rush hour from 6 to 9 a.m. That configuration is reversed for the evening commute from 3 to 7 p.m., with four westbound lanes, a center turn lane and two eastbound lanes. While the new flex lanes have caused some confusion from motorists, the UDOT Deputy Director Tim Rose dismissed these claims. "All you really need to do is look above your head, and if you see a red 'X,' you're in the wrong lane and need to get to the right immediately and move along," Rose said .
SImilar to the W 5400 S project, the Ross Island Bridge is ripe for flex lanes installation. The Ross Island Bridge carries a similar number of motorists per day (50,000 compared to 41,000 on W 5400 S), and also features a long segment of uninterrupted highway with little pedestrian or bicycle traffic. The W 5400 S corridor has significant challenges when dealing with turn lanes and intersection treatment - the Ross Island Bridge has none of these issues being that it is a bridge, reducing installation cost and improving safety.
Design of the Ross Island Bridge Flex Lanes
The design of the Ross Island Bridge flex lanes should go beyond supporting the movement of vehicles. As previously mentioned, the planned Powell Boulevard Bus Rapid Transit (BRT) will greatly benefits from an improved passage across the Ross Island Bridge. Currently, TriMet designates four bus lines across the Ross Island Bridge, including the 6-Marquam Hill, 17-Holgate, 19-Woodstock, and the frequent service line of the 9-Powell slated for BRT . Flex lanes have the opportunity to accommodate a transit-only lane across the Ross Island Bridge, encouraging higher transit ridership for a congestion free ride. With a transit only lane, TriMet can maintain speedy service, and possibly divert more bus routes across the Ross Island Bridge to better serve Southeast Portland.
The existing configuration of the Ross Island Bridge is two eastbound and two southbound lanes as shown in Figure 3A. The proposed design would have three westbound (inbound) lanes and one eastbound (outbound) lane for AM peak hours as shown in Figure 3B. PM peak hours would reverse the flex lanes, with three eastbound lanes and one westbound (Figure 3C). During off peak hours, the flex lanes would balance out for two eastbound and two westbound lanes (Figure 3D). Unlike standard flex lane projects, the third flex lane during AM and PM peak hour times would only be allowed use by transit and emergency vehicles. This would ensure not only swift travel for transit commuters, but also avoid confusion by drivers by limiting travel to two lanes. Similar to the W 5400 S project in Utah, lane direction would be indicated overhead with a red “X” and green arrow.
|Figure 3A: RI Bridge existing conditions, Source |
|Figure 3B: RI Bridge flex Lanes AM peak hour, Source |
|Figure 3C: RI Bridge flex lane PM peak hours, Source |
|Figure 3D: RI Bridge flex lanes off-peak hours, Source: |
Looking Towards the Future
Flex lanes on the Ross Island Bridge would not solve all congestion issues, but it would be a significant improvement for mobility across the Willamette River. With the construction of the new Milwaukee Light Rail Bridge in progress, there is an opportunity that some bus routes will utilize the new bridge and bypass the Ross Island Bridge. If the transit lane is no longer needed along Ross Island Bridge, the third peak lane could be redirected for vehicle use, thereby still having improved capacity and flow.
The Ross Island Bridge flex lanes should also serve as a pilot study for future use in the Portland area. Corridors such as Barbur Boulevard and SW Beaverton-Hillsdale Highway could potentially benefit from installation of flex lanes.
 Traffic Volumes on State Highways. ODOT. 2011.
 Park, Young. “Powell-Division Transit
 Deseret News. “Utah's first flex lanes system opens on 5400 South in Taylorsville.” http://www.deseretnews.com/article/865566239/Utahs-first-flex-lanes-system-opens-on-5400-South-in-Taylorsville.html?pg=all http://streetmix.net/