Pervious Pavement and Street Width in Portland

I was visiting some friends in Portland when I happened upon some unique paving. Instead of the street consisting of one solid slab of asphalt, the asphalt was limited to the narrow travel lane. The parking lanes were paved with brick-colored pavers. After I returned home, I did some research and found that this was a City of Portland, OR pilot project to test a couple of pervious paving schemes.

Portland’s pervious paving experiment

The street above is one of a few the city did in the Sellwood/Westmoreland neighborhood to mitigate the effects of storm water runoff after heavy rains. Portland has been on the forefront of storm water mitigation at the source, but usually through the use of bioswales. This treatment allows rainwater to flow off of the asphalt and into the parking lanes, where high-strength concrete pavers allow rainwater to flow down the spaces between them. The layers below the pavers filter out pollutants that would otherwise contaminate the groundwater.

While I really like this approach to managing storm water, I am most interested in this as a bit of urban design. This street looks like it is about 30 feet curb-to-curb, with two eight-foot parking lanes, two one-foot curbs between the lanes, and about twelve feet of asphalt for the queuing travel lanes. The idea on this street is that when two cars pass each other, one slows or stops in the parking lane to allow the other to pass. It’s a condition that results in slower speeds, perfect for residential neighborhoods like this.

This scheme really makes the street feel narrower and more appealing. A 30-foot-wide street on a quiet residential block is a bit overkill and out of scale for the place. Reducing the ocean of asphalt to a pleasant strip is a step in the right direction. The addition of pavers adds some human-scale texture to the street — another plus.

The same street, with less on-street parking

The scheme also highlights an absurdity in residential street design. Namely — does this street really need two sides dedicated to off-street parking? Taken together, parking takes up over half of the street area and it’s used by maybe three cars in this picture. In places where there is plentiful off-street parking, this much on-street parking seems like a waste. The different pavement treatments really shows off this ridiculous allocation of space. Imagine if one side of the parking was removed, and the curb-to-curb width was only 22 feet (the quick photoshop at right). The result is much more intimate and better proportioned to the area the street serves.

Even with the street at the present width, the new pavement treatment is a success on a couple of levels. The storm water entering the sewer system will undoubtedly be less, and the street is far more attractive than a plain asphalt-only one. It’s not within the City of Portland’s capabilities to stretch the fabric of the earth to reduce the width of the street like I did above, but it shows that new streets do not need to be built to the same specifications.