#23 – Crossing an Arterial through an Offset Intersection: Bicycle-Only Center-Turn Lane

Portland, Oregon

Roger Geller, Bicycle Coordinator, City of Portland, Oregon

Background

Rendering of bicycle-only center-turn lane.

Photo of bicycle-only center-turn lane as implemented.

The North-South 40s Bikeway is a 12.2 km (7.6 mi) bicycle corridor about 4 km (2.5 mi) from Portland’s downtown core. Developed in 1999, the bikeway runs the entire breadth of Portland from north to south, connecting residential neighborhoods to five commercial districts, six parks and 10 schools and intersecting 10 perpendicular bikeways. It comprises 9 km (5.6 mi) of bicycle boulevards, 2.9 km (1.8 mi) of bicycle lanes and 152.4 m (500 ft) of off-street path¹.

A minor arterial with an average daily traffic of about 10,000, SE Stark Street, intersects a segment of the bikeway on SE 41^st Avenue. The junction is complicated by a 35 m (115 ft) offset of 41^st as it crosses Stark. North and south approaches are stopped with stop signs. The standard set of crossing treatments were considered but posed significant drawbacks for this project. The only effective civil option would have been a median refuge, which would have prohibited some turning movements from Stark to 41^st.

Countermeasures

In the end it was decided to stripe a bicycle-only center-turn lane. This two-way, 3 m (10 ft) lane provides a refuge for cyclists who cross Stark by essentially executing first a right-turn onto Stark and then a left-turn back onto the bikeway.²

Evaluation and Results

There has been no formal evaluation, but feedback from cyclists has been positive and the intersection continues to function as intended.

Conclusions and Recommendations

This treatment successfully addressed three criteria: it offered a refuge for crossing cyclists and allowed them to cross one direction of traffic at a time; it maintained all automotive turning movements, and it provided an inexpensive solution to this crossing that left more available funding for conventional civil treatments at other intersections on the bikeway.

Costs and Funding

Costs for thermoplastic paint to make the bike markings were minimal. The project was implemented as part of a larger plan, so there is no break-out for this treatment.

Contact

¹Portland stripes bicycle lanes on roads with average daily traffic volumes of 3,000 or greater. Bicycle boulevards are low volume streets that generally work well for bicycling. The city typically improves arterial crossings, alters the stop sign pattern, and occasionally diverts automotive traffic to make them work better.

²We considered two options — crossing making first a right turn and then a left turn, or using the next street to cross making first a left turn and then a right turn. Doing the latter would require only striping receiving bicycle lanes on the cross street. We rejected that in favor of the right-turn first scenario because to make the left turn first would necessitate crossing both lanes of cross traffic at once, rather than crossing one lane at a time, as is done when making the right turn first.