Urban and suburban streets should be structurally sound and safe for motorists, pedestrians and bicyclists. Ideally, they should also be beautiful.

But many are less than ideal, plagued by broken curbs, potholes and crumbling sidewalks or no sidewalks; dead trees, the wrong trees or no trees; lack of crosswalks; poor street lighting; overhead wires strung between utility poles; and obscured or inadequate signage.

Planning, constructing and maintaining streets is not just a utilitarian matter. Streetscapes constitute the public realm we all see, share and use every day. Designing that realm, like designing good architecture, should aspire to achieve aesthetic as well as practical goals. A good street is a public place, one that can be visually appealing as well as functional and sustainable.

You know nice streetscapes when you see them. They may be relatively intimate, historic urban streets, like those in Old Town Alexandria, Annapolis, Leesburg and Georgetown, framed by buildings close to or abutting the right-of-way. Perhaps you recall attractive, memorable streets you have walked in Boston, New Orleans, San Francisco, London or Paris.

Lanes, avenues, boulevards and parkways — urban and suburban — often are visually delightful thanks to continuous borders of healthy deciduous trees. Street-flanking tree trunks and branches form rhythmic colonnades parallel to the roadway and provide overarching leaf canopies, creating a pleasurable sense of streetscape enclosure.

(Roger K. Lewis)

Most of us take streets for granted, unaware of the many streetscape design issues and elements. Some are obvious: roadways and sidewalks, curbs, paving materials, parking, trees and vegetation. But the menu of design concerns also encompasses stormwater collection and retention, utilities ideally installed entirely underground, crosswalk placement, traffic signals, bike lanes, lighting, street signs and street “furniture” — benches, trash receptacles, information kiosks, bus stops.

Too many streets are shaped by handbooks, especially streets built outside older, central city neighborhoods and suburbs. Detailed standards prescribed in roadway engineering manuals, along with appended supplements adopted by local transportation agencies, in effect generate street designs. Once a street is classified by type and traffic load, engineers can simply rely on widely used, conventional standards for design and construction.

Applying conventional standards may be necessary but is never sufficient. To achieve visual quality, to offer aesthetically satisfying experiences for users, street design must go beyond conformance with technical criteria. Creating a beautiful, durable and ecologically sustainable streetscape requires a multidisciplinary team. Talented urban designers, landscape architects and graphic designers, in addition to technically proficient civil and environmental engineers, must work collaboratively.

To meet vehicular needs, the team begins by establishing road alignments and dimensions, paving materials, base courses below the paving, and stormwater management systems. But the team also needs to consider street space proportions — the relationship between street widths and heights of buildings facing a street.

Sidewalks likewise deserve special attention. Based on sidewalk function, the team must focus on materials and textures, patterns and colors, water permeability and width. A four- or five-foot-wide sidewalk serves only pedestrians. To comfortably accommodate pedestrians as well as outdoor eating and street trees, a sidewalk needs to be at least 20 feet wide. Add four to six more feet if including a bicycle lane.

For street trees, selecting and placing appropriate species is crucial. Selection factors include tree survivability — vehicle exhaust fumes can kill trees — plus drought resistance, leaf debris production, and canopy size and shape affecting shade and future growth. The wrong trees badly placed can impede sightlines, blocking desired views of buildings and compromising safety at intersections and driveways.

Street lighting enhances public safety while helping animate streetscapes after sunset, especially in commercially active areas. But lighting can be insufficient, and regulations may be minimal. Many suburban jurisdictions require relatively little street lighting along subdivision streets where homeowners object, understandably, to glare produced by off-the-shelf street lights. But if properly positioned within a streetscape, wisely designed light poles and fixtures, shielded to eliminate light spillage and glare, can provide desirable illumination — neither too little nor too much — without pouring light through nearby windows.

Signage — locational and identification signs, directional signs, parking signs — present another design challenge teams must address. Signs too often are awkwardly placed, poorly illuminated, or obscured by trees, shrubs, structures or dirt. Some are hard to read because they contain too much text or text that is too small. And who has not been annoyed by invisible or missing building address numbers, so important for first-responders and deliveries as well as visitors.

Implicit in all these streetscape design considerations is the need to anticipate and plan for cost-effective maintenance: repairs and repaving; the removal of debris, snow and ice; and perhaps right-of-way and roadway widening to accommodate greater traffic flow.

Compared with the cost of engaging a team to collaboratively design a street, the cost of construction and then decades of maintenance is enormous. Yet the payoff of high-quality design can be big: a beautiful, sustainable public space through which driving, walking and biking is a delight.

Roger K. Lewis is a practicing architect, a professor emeritus of architecture at the University of Maryland, and a regular commentator on “The Kojo Nnamdi Show” on WAMU 88.5.