Building Pedestrian Infrastructure With or Without Constraints

A closer look at how the technical factors of topography and existing stormwater infrastructure influence new sidewalk construction with development. Reasons the city seeks alternative pedestrian connections in lower-density residential zones.
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Portland’s Citywide Pedestrian Plan, PedPDX, outlines our city’s values: make walking safer, more accessible, and an attractive experience for everyone by putting pedestrians at the forefront of city policy, investment, and design.

Portland’s sidewalk network has been built out incrementally over the decades, through city investment and capital projects, as well as through requirements of developers constructing new buildings or doing major renovations. 

In flatter areas of the city and in places where there is already a curb and gutter system for stormwater, building a sidewalk is typically straightforward. It requires an inexpensive minor improvement permit. 

Below, we look at two technical factors that can make building sidewalks much more challenging and expensive: topography and lack of stormwater infrastructure. Both of these factors are looked at closely during the development review process because they may require more extensive engineering and construction, raising costs significantly. 

For larger projects these added costs have less of an impact relative to the scale of the development. For some small residential projects, however, it might be cost-prohibitive.

The city determines which improvements are appropriate for each situation. In some cases, the city may approve an alternative to standard sidewalk construction in lower-density residential zones on streets that are not eligible for the Local Transportation Infrastructure Charge.

Building sidewalks with no constraints

For most development, the land looks something like the illustration below. This 100-foot-wide property is relatively flat and there is already a curb and infrastructure for stormwater runoff. This work has few if any constraints.

A property with flat land and an existing curb, gutter, and sewer.

Constructing a sidewalk here is relatively simple (see illustration below). Sidewalks simply require poured concrete behind the existing curb, with aprons for driveways as needed. If the length of sidewalk is less than 100 feet, developers pay a nominal minor improvement permit fee as well as any construction and material costs. Construction, engineering, and permitting costs will increase if a corner must be built or rebuilt. 

Building sidewalks with no constraints. A house has been built on a flat property with existing curb and gutter. The steps to build a sidewalk are: build sidewalk behind the existing curb and build the apron for the driveway. A minor improvement permit is required for this work.

Building sidewalks or shoulders with constraints

Building a pedestrian network gets trickier, and more expensive, where there is challenging topography and/or no existing curb. In such places, stormwater typically flows off the road into an adjacent ditch or culvert. This scenario makes it much harder to build sidewalks. 

A property with challenging topography. Water flows off the road into an adjacent ditch.

Scenario 1 – Building sidewalks with constraints

For instance, the scenario pictured above may need a new curb, retaining walls, more engineering, and/or extensive stormwater infrastructure before building a traditional sidewalk (illustrated below). This would require a public works permit which start at $5,000. Engineering and construction costs may also be substantial. In some cases, this will require a sidewalk narrower than city standards.

Building sidewalks with constraints. A house has been built on a steep sloping property on a street with no curb. The steps to build a sidewalk are: build large retaining wall, build new curb, build sidewalk behind new curb, and build extensive permitted stormwater infrastructure. A new concrete driveway can be built. A public works permit is required for this work.

Scenario 2 – Shoulder widening

One alternative to a traditional sidewalk is widening the shoulder to give pedestrians more space. A public works permit is still required, but a wider shoulder forgoes the need to construct a curb, simplifies the drainage, and requires less space, so retaining walls don’t have to be as large. In some instances, though, this will be infeasible because of topography or other factors.

Building shoulders with constraints. A house has been built on a steep sloping property on a street with no curb. The steps to build a shoulder are: build smaller retaining wall, widen shoulder, relocate ditch, and connect the existing ditch to the relocated one. A new asphalt driveway can be built. A public works permit is required for this work.

How the city decides

The city decides on the appropriate pedestrian improvement for each specific situation. To do this, the city evaluates the complexity of addressing topographic constraints and managing stormwater, as described on this page. There are several other factors that influence the decision as well. These include, but are not limited to: whether a curb exists already, the size of the development, the length of the frontage, whether the property is in an environmental or other overlay zone, and the type of walkway present on other parts of the street. If there is no existing curb and the development is small in scale, the solution may be shoulder widening. If there is a curb and/or if the development is larger, then the solution is more likely to be a sidewalk.  

In some instances, the work to design and engineer the sidewalk or shoulder may result in approving a less than standard sidewalk or reveal that shoulder widening is infeasible due to severe topography and/or stormwater constraints. Requests to consider alternatives to improvements required by PBOT are evaluated through the Public Works Alternative Review Process.