By Kathryn Piasecki, EIT, AICP, with contributions from Mengyao Li, AICP; Madeline Augustine, PE; and Nicole Holmes, PE, LEED AP
Urban environments are confronting mounting pressures from climate change, aging infrastructure, and growing demands for safer, healthier communities. In response, Nitsch Engineering’s planners and engineers are embracing integrated design approaches that address these challenges holistically. This article explores how intentionally coupling resilience strategies with traffic calming and pedestrian safety improvements can deliver greater value from streetscape projects – transforming everyday roadways into vibrant, sustainable public spaces that support people, ecosystems, and communities.
Optimizing Street Design: Coupling Resilience Strategies with Traffic Calming
Urban streets are more than thoroughfares for motor vehicles: they are public spaces where people walk, shop, and come together, playing a vital role in a community’s social and economic fabric. Historically, street design has prioritized vehicles, encouraging faster traffic and creating situations where pedestrians and cyclists often encounter conflicts with cars. Motor vehicle-focused transportation design results in wide travel lanes with high impervious cover, constraining pedestrians to a relatively small portion of the right-of-way and contributing to unsafe conditions for cyclists and pedestrians sharing the street. Strengthening road safety and pedestrian and cycling infrastructure are essential to reducing fatalities and designing streets for all modes of transportation.
When communities treat urban streets as shared public spaces rather than vehicle corridors, they can create safer, more inclusive environments for all users. Car-centric design – characterized by wide streets, minimal visual cues, and limited crossing opportunities – encourages higher vehicle speeds and creates unsafe pedestrian crossings. These conditions make urban streets dangerous, with traffic accidents ranking among the leading causes of death and injury in the United States. Designing streets to reduce speeds and minimize conflicts is essential to safely accommodate users of all ages and abilities across all modes of travel.
Urban streets are also a major source of pollution in cities, with runoff carrying sediments, microplastics, oil, deicing salt, nutrients, and other pollutants into nearby ecosystems. Paved streets are a major driver of both the urban heat island effect and urban flooding, as impervious surfaces retain heat and prevent stormwater from infiltrating into underlying soils. As climate change brings more extreme weather events, including more intense storms, periods of drought, and rising temperatures, it is crucial for urban corridors to be adapted to be more resilient to these climate stressors. According to the National Association of City Transportation Officials (NACTO), public rights-of-way typically make up more than 80% of a community’s publicly owned space, making streets a prime opportunity for implementing widespread resilience measures.
To address compounding challenges, communities are increasingly viewing streets as multi-functional public spaces that create opportunities to address safety, health, and environmental goals holistically. Integrating active transportation and green infrastructure into street designs enables communities to align safety, resilience, and placemaking goals within a single, cohesive approach. Thoughtfully designed streetscapes support public health, safety, and community connectivity, particularly for pedestrians and cyclists, while also enhancing ecological function and stormwater management. Coupling these strategies maximizes community benefit and unlocks the full placemaking potential of urban streets, yielding co-benefits such as improved water quality and a more resilient built environment.
Design Considerations that Support Implementation
The geometry of most streets makes mid-block crossings and intersections prime locations to couple green infrastructure with traffic calming strategies, simultaneously managing stormwater while improving pedestrian and cyclist safety through shorter crossings, better visibility, slower vehicle speeds, and narrowed lanes.
Many existing streets are designed with a crown, creating a slope that directs runoff toward gutters and away from the center of the street to prevent standing water. This geometry creates favorable conditions for incorporating linear green infrastructure between the vehicular zone and pedestrian zone, typically in the form of bioretention planters, tree filters, or permeable pavers. Most existing streets are also designed with a longitudinal slope to direct the water in the gutter towards catch basins, typically situated at mid-block and end-block locations. This geometry further creates favorable conditions for incorporating green infrastructure around mid-block crossings and intersections, typically in the form of bioretention curb extensions.
Additionally, parking is typically prohibited near intersections and street corners to improve visibility and safety for both drivers and pedestrians. These existing restrictions mean that installing green infrastructure in these locations often does not require the removal of on-street parking, helping to overcome a common barrier to implementation in commercial and residential districts.
Precedents for Safer and More Resilient Streets
The following examples from Boston and Washington, D.C. illustrate integrated strategies that have been successfully implemented within the public right-of-way to improve safety, resilience, and the overall streetscape experience.
Pinchpoints and Bioretention
Curb extension at pinchpoints slow traffic and improve pedestrian safety by shortening crossings, enhancing sight lines, and narrowing travel lanes. Pinchpoints can also be utilized at mid-block crossings to shorten the crossing distance for pedestrians or at bus stops to improve the experience for bus riders. Pinchpoints not only calm traffic and reduce conflicts among all roadway users but can also be optimized to enhance public open space, creating a valuable opportunity for green infrastructure solutions, such as tree pits and bioretention planters. Bioretention planters utilize plants and engineered soil sections to filter and absorb stormwater, improving water quality and reducing localized flooding, while also adding greenery to the streetscape.
Porous Materials for Visual and Environmental Impact
Porous surfaces, such as permeable pavers and porous asphalt, allow rainwater to percolate into the ground, reducing runoff and supporting groundwater recharge. These materials can be integrated into parking lanes, furnishing zones, and curb extensions to enhance stormwater management. Porous surfaces can also help separate pedestrian zones from active driving lanes, creating visual contrast and encouraging drivers to reduce their speeds.
Lane Narrowing and Enhanced Pedestrian/Cycling Zones
Narrow lanes can help reduce speeds by increasing driver awareness of adjacent traffic and multi-modal users. Narrower vehicular lanes also make more space available within the right-of-way, which can then be reallocated to provide additional amenities to active transportation users, such pedestrians or cyclists.
Enhanced pedestrian zones can consist of a variety of different elements, such as trash receptacles, bus stops, signage, or bike share stations, in addition to green infrastructure, such as tree pits or parklets.
Extra space within the right-of-way may also be used for curbside bike lanes or cycle tracks, with planted buffers or landscape strips providing protection for cyclists.
Gateway Treatments and Curb Extensions
Curb extensions expand pedestrian zones, shorten crossing distances, improve visibility and safety of pedestrians, calm traffic, and provide valuable space for green infrastructure such as bioretention cells and tree pits. When applied at the mouth of an intersection, these curb extensions are often referred to as a gateway treatment, marking the transition to a slower speed area, highlighting the change in street type to drivers, and enhancing the sense of place for all modes of transportation.
Visual Perception and Tree Filters
Street trees add visual friction, encouraging drivers to reduce their speed. A narrower field of vision encourages reduced speeds and thereby increases the sense of safety for roadway users outside of motor vehicles. Trees also create benefits at the pedestrian scale, offering shade, improving air quality, and absorbing polluted runoff. Engineered tree pits, often combined with structural soil and suspended pavements systems, improve stormwater management and support healthy root growth for street trees, contributing to both ecological health and flood resilience.
Conclusion
Climate change is intensifying the need for resilient infrastructure in cities. Extreme weather events, flooding, and heat waves threaten urban areas, making it essential for urban corridors to withstand and adapt to these stresses. Meanwhile, public safety, health, and community connectivity initiatives are emphasizing the need to consider traffic calming strategies that reduce vehicle speeds and provide pedestrian-safety environments that consider safety for all road users.
Coupling green infrastructure and resilience strategies with traffic calming has transformative potential for urban streets. By adopting an integrated approach, planners, engineers, and community leaders can create streetscapes that are safer, healthier, and more resilient, delivering lasting benefits for multi-modal users. When streets are redesigned, municipalities can reallocate space towards both active transportation facilities and green infrastructure, doubling the benefits of the streetscape. Furnishing zones, buffer space, and curb extensions can be maximized through infrastructure that also provides resilience benefits.
What’s Next?
Keep an eye out for upcoming articles that explore holistic approaches to streetscape design in greater detail!