Thursday, June 6, 2013

“Flexing” the Ross Island Bridge for BRT

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 [1]. 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 [3].

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 [2].   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 [2]. 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 [4]. 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 [4].

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 [4].

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.

Figure 2:Typical Flex Lanes Operations. Source [2]

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 [5].  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 [6]

Figure 3B: RI Bridge flex Lanes AM peak hour, Source [6] 

Figure 3C: RI Bridge flex lane PM peak hours, Source [6]
Figure 3D: RI Bridge flex lanes off-peak hours, Source: [6]

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.

[1] Traffic Volumes on State Highways. ODOT. 2011.
[3] Park, Young. “Powell-Division Transit
Alternatives Analysis”
[4] Deseret News. “Utah's first flex lanes system opens on 5400 South in Taylorsville.”


  1. I would hardly call the 5400 South project something to emulate and is typical of how a department of transportation is so worried about moving traffic as fast as possible, everything else does not matter.

    A few years ago I was transferred down to Utah and in fact lived just a mile or two south of 5400 South on Redwood Road where this project starts.

    First of all, 5400 is not a suburban highway but a primary connecting road that runs through neighborhoods. What UDOT has done is turn this road into a superspeedway that is not safe for pedestrians to walk along or cross plus don't get near the thing on a bicycle.

    I took some pictures of this glorious UDOT project a few months ago. It is very confusing to drive for the average person and the signs are actually a distraction when driving it at night.

    In addition it is horrible urban design that has cut off several neighborhoods the same way a freeway would have and businesses although few in number are losing revenue because people will not shop along the corridor.

    On the other hand many of those problems would not be situation with the Ross Island bridge, but if moving buses faster is the point, since bus service is going to be moved to the new Tri-Met bridge in 2015, should we really go to this effort?

  2. This actually seems like a really good and cost-effective way to maintain the "rapid" part of BRT. Do you know if TriMet has considered this as an actual alternative if the PMLR bridge can't accommodate BRT service levels?

  3. << A bridge replacement or expansion on the Ross Island Bridge would be costly and followed by years of design and construction. >>

    You hit the nail on the head for a near immediate, cost-effective solution to congestion management, Max. The Ross Island bridge is a significant beast to tackle and obviously Flex lanes may not be an end all solution but it is a smart, quick fix that could have serious benefits.

    I have also driven on flex lanes before, but unlike John, I didn't find them confusing, they were perfectly clear so long as you were simply paying attention to what was going on. Like Tim Rose said, "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," It's not rocket science and I feel like the symbology used and color theory assigned to it is fairly clear for general traffic standards in the United States.

    Great post!

  4. Just to be clear I myself did not find them confusing, however, I saw many drivers who were confused by signs. Remember common sense is not very common.

    Second I feel that most of problems with the Ross Island Bridge would be solved if they made the changes that have been recommended as part of a redesign of the west side of the bridge (I know costly but needed). This plan would make direct connections from I-5 to the bridge eliminating the strange paths you have to use to get between the two, and taking out the connections to Naito Parkway as part of revamping that street.

    Also how much of the traffic on Ross is being caused by people avoiding the construction on the Sellwood Bridge and once that is done will it help eliminate some of the problems.

    Once the PLMR is done, Sellwood is done, and if they revamped the west end of the bridge would this truly be needed. While the proposal is innovative are we falling into the trap of over engineering a problem and actually making conditions worse?


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