Editor’s Note: One of the missing voices in bicycle planning in the Twin Cities is college students who belong to a generation much less likely than their parents to own vehicles. This series of posts written by Macalester students for the “Bicycling the Urban Landscape” course are one effort to include these voices. This piece was contributed by David Munkvold, a senior at Macalester College who bikes everywhere. If not on his bicycle, he might be slack-lining, programming, playing music, or meditating. David is very interested in the infrastructure of the Twin Cities as he will continue to live here after graduation.
Coming from a medium-sized Midwest town with little bike infrastructure, I have always viewed urban cycling as a kind of puzzle. There is a start point and an end point, and finding the sequence of surfaces that allows me to reach my end point without any bodily injuries is the challenge. After moving to St. Paul to attend college, I was initially relieved of this perspective, as the dense bike network of the Twin Cities made me feel as though my routes were no longer problems to be solved, but yellow brick roads leading to my destination . However, after biking year-round here for four years, I have come to realize that as a cyclist, there are always struggles to find appropriate surfaces to traverse upon. Where at home it was a lack of infrastructure, here it is the ice, snow, and rampant road decay that present obstacles to safely riding in the city.
There are many instances in which our wonderful bike paths are made obsolete by our latitudinal condition. Ice and snow that cover the roads make it impossible to bike without certain tires. Plowing of the streets results in pile-ups of snow in bike lanes or parking lanes, and residents aren’t afraid of encroaching on the bike lane when there isn’t enough room for their vehicle. For example, on Marshall Avenue in St. Paul, there are stretches of road where snow piles block the parking lane and motorists park in the bike lane. There are few streets with bike lanes that are wide enough to hold plowed snow, bikers, and motorists without overlap. When the snow and ice melt away, they leave deep puddles and cracked concrete in their wake. Even in the middle of the summer, the erosion of the road surfaces can make it difficult to bike on many streets and paths. On the western end of Summit Avenue in St. Paul, which was resurfaced about five years ago, the erosion has produced street-wide cracks that occur at regular distances, making it taxing for cyclists who must endure a rhythmic test of skeletal integrity.
Many are content to deal with these challenges because they seem to be unavoidable truths of living in a colder climate. While we cannot do anything about the cold air, the snow, ice, or sleet, we can do something about the surfaces that withstand (or fail to withstand) these features of harsh northern winters.
A road surface’s biggest threat in colder climates is moisture. Most road surfaces are relatively water-proof, and we expect that the moisture will either run off into the gutter or evaporate. Due to the material properties of asphalt and concrete, however, water inevitably finds its way into the road surface and becomes trapped. During the winter, this water freezes and its volume increases by around 9% of its original volume. This expansion creates tension in the road surface and eventually breaks it up from the inside. Not only does the water inside the road surface freeze, but any water that was on top of the road also freezes, creating dangerous conditions for drivers and bikers alike. The freezing of moisture inside and on top of the road during the winter make it less safe year round, either through ice/snow or deteriorating street surfaces. How can we keep moisture away from the road so that we can avoid dangerous transportation conditions?
Rather than finding ways to keep moisture away from road surfaces, St. Paul has decided to implement a bike path downtown with a surface that actually soaks up moisture. Pervious concrete, the idea for which has been around for centuries, allows water to pass through it into a reservoir underground. Water doesn’t accumulate on top of pervious concrete, so cyclists won’t have to ride over ice and snow. Water doesn’t accumulate within the concrete either, so volume expansion due to freezing is not necessarily an issue. It’s too early to tell how effective the surface is, but if it is at least as durable as the materials we use now, then we should begin using them across the city, and not just for bike lanes.
Hypothetically, if our roads soaked up water, we wouldn’t need extra space for storing snow. Provided that the reservoir was built deep enough to avoid saturation of the concrete, then the snow should be able to pass through it and into a network of runoff that can be managed more easily than runoff from waterproof concrete. Less snow storage means more room to drive, bike, or walk and safer conditions overall during the winter months. It also means that there is less moisture trapped in the road surface that could freeze and damage the concrete. Not only is pervious concrete potentially more durable than concrete, but it can be cheaper to construct. Conventional concrete and asphalt roads require the construction of above and below ground storm water retention ponds and gutters. Pervious roads require smaller capacity storm sewers that only need to be underground.
Although pervious concrete is cheaper to install, it does require maintenance. Debris must be regularly vacuumed out of the concrete to prevent clogging of the porous material, or else water will become trapped inside and the road will be subject to cracking and buckling. Considering that the city would not have to devote as many resources to plowing the streets during the winter and repairing the streets during the summer, it is a small price to pay.
It will be crucial to keep an eye on the pilot pervious path in downtown St. Paul for the next few years and be prepared to make some changes to the way that we think about surfaces in an urban environment.
Sources
Montgomery, David. “How Does Minnesota Maintain Its Roads?” Twin Cities. Twin Cities, 18 Apr. 2016.
Washington State Department of Transportation. WSDOT STRATEGIES REGARDING PRESERVATION OF THE STATE ROAD NETWORK.