One-way couplets are pairs of parallel streets separated by a city block, where each street allows traffic to move in one direction only. This strategy has been used in traffic engineering to improve traffic flow, manage congestion, and allow for vehicles to move through the streets more quickly. These couplets became popular in the middle of the 20th century as urban traffic management and city planning evolved to address higher levels of car usage and to reduce traffic in urban areas.

Many urban areas from big cities to small towns implemented this system of traffic management as it was believed that this would reduce the number of crashes, as well as traffic and congestion. However, some towns and cities are now converting back to a two-way traffic system, as one-way couplets allow increased speeds, more car-centric cities, and some argue more accidents as cars are moving at a faster rate and expect to get the right of way, not always being conscious of pedestrians and cyclists. 

This shows the full one-way loop of Main St. and Petaluma Ave.

The town of Sebastopol converted to one-way couplets in the 1980s. The one-way couplet system in Sebastopol consists of the paired streets of Petaluma Avenue and Main Street and was implemented to improve traffic flow and manage vehicle congestion in the downtown area. The priority at the time seemed to be to increase vehicle throughput and reduce traffic. Sebastopol is a crossroads town. There are a lot of vehicles that are only passing through town in both the east-west and north-south directions so we do see a relatively high level of auto trips per day for a city of 7,600 people. All of those trips pass through the center of town. The east-west route consists of one lane in each direction. It does have a center turn lane for several blocks east of downtown. The north-south route has one, two or three lanes at times.

The multiple one-direction lanes on Main Street really does have a negative impact on the pedestrian experience downtown. For one, the primary commercial block of downtown between McKinley and Bodega Ave. is 3 lanes, in one direction! Just a block to the north it is a single lane. I don’t understand why 3 lanes are necessary, other than the fact that the space is there. The lanes were wider at one point but a separated bike lane has been added to the west side so the lane width was reduced a bit. But the impact on the pedestrian is a lot of asphalt and cars. It just doesn’t have the feel of a charming small town downtown. It feels more like a highway. And while this is a Caltrans right-of-way, it doesn’t need to feel like a highway. We should be prioritizing people downtown and not cars.

Southbound Main St. is highlighted. Petaluma Ave is the street to the left.

This southbound section of Main St. really becomes a speedway after vehicles leave the traffic light at the bottom of the above image. After leaving the traffic light at Bodega, Main Street is two one-way lanes for about 1/2 mile until the two one-way streets join again. At this point it becomes a single-lane in each direction with a center turn lane. Drivers heading south on Main know that they need to merge within a half mile if they intend to continue south. While the speed limit is 25 mph near downtown it inexplicably increases to 30 mph about halfway between downtown and the split.

View of S. Main where the speed limit is 25 mph.

A couple blocks further south, the speed limit increases to 30 mph even though it’s a very similar environment.

I walk this section of road several times a day between my home and office and while I don’t have a speed detector, people regularly drive more than 30 mph. Some people are easily driving at more than 40 mph. It just doesn’t feel great as a pedestrian. It’s also a great example of how speed limit signs do little to keep speeds in check. People will drive as fast as they feel comfortable. The lanes are comfortably wide (I think 12′) and straight. If this section of road were to be converted back to 2-way people would be forced to drive much slower partly because there would be no racing to pass people before the road goes back to a single lane and because of the natural ‘friction’ people would feel with cars coming towards them in the adjacent lane. I will say the addition of a bike lane on the west side of Main St. has been helpful with slowing traffic (the lanes used to be 18′ wide each!) but more needs to be done to make this a safer and more pleasant environment.

The couplet split south of downtown.

The split of lanes south of downtown.

The northbound Petaluma Avenue is a single lane with a separated bike lane for 1/2 mile when it widens to 2 lanes at the Joe Rodota Trail and then to 3 northbound lanes two blocks south of Sebastopol Ave. The right lane really becomes more of a slip lane at the intersection with Sebastopol Ave. Cars often move much slower on Petaluma Ave. particularly when there is traffic. Since it is only a single lane there is no passing, or jockeying for position like on Main Street. People do get frustrated at how slow cars move during traffic times, but as a pedestrian or bicyclist, I feel much safer when cars are moving slowly. It also feels great to bike faster than vehicular traffic is moving!

Petaluma Ave. intersection with Sebastopol Ave.

In recent years there have been discussions in the city about revisiting the effectiveness of the one-way couplet system given the current understanding about some of their negative impacts. Negative impacts include encouraging speeding, navigation confusion (I often see drivers going the wrong way on Main Street), safety, and business exposure. For a downtown commercial district cars really dominate the environment, and are given priority. The pedestrian experience is secondary. The downtown street network has been designed to move as many cars as possible as quickly as possible. This hurts the vitality of downtown as it feels more like a place to pass through rather than a place to be.

Sebastopol was recently awarded the CalTrans Sustainable Transportation Planning Grant, which will include a study of the one-way couplet system and determine if changes should be made. This reflects a broader trend in urban planning where cities are reconsidering the role of one-way couplets in light of contemporary priorities like pedestrian safety, multi-modal transportation, local business access, and overall urban livability​.

There will be an opportunity to express your opinion about the Sebastopol downtown couplet along with all other things related to improving Main Street and Petaluma Avenue on November 14th at the Sustainable Transportation Planning Grant first community workshop. The event is from 3-7 PM at the Center for the Arts. For more information, click here . To take the online survey, click here.

Hope to see you there.

Thanks to Anya Lee Brink for research and a first draft of this post.