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Transit is returning to its central place in the life of cities. With more people using buses, streetcars, and light rail than ever before, our street design paradigm is shifting to give transit the space it deserves. People are choosing to live, work, and play in walkable neighborhoods, and cities are prioritizing highly productive modes like transit as the key to efficient, sustainable mobility for growing urban populations. Transit agencies and street departments are working together to create streets that not only keep buses and streetcars moving, but are great places to be. Cities are extending light rail systems, investing in streetcar lines, and creating new rapid bus lines at a stunning pace, with ridership growing even faster in city centers. Transit agencies are rethinking their networks to serve neighborhoods at a high level all day, not just at commute times, while bike share and active transportation networks make it even easier to not only reduce driving, but to avoid the expense of owning a car.
At the heart of these changes is the need for cities to grow without slowing down. Transit is a key that unlocks street space, bringing new opportunities to create streets that can move tremendous numbers of people and be enjoyed as public spaces at the same time.
Cities around the country and around the world are finding new ways to create these places. To codify and advance best practices in transit design, the National Association of City Transportation Officials has brought together practitioners and leaders from the transit and street sectors to develop theTransit Street Design Guide. This new framework for designing transit corridors as public spaces will help cities and their residents work together to create the streets that are the foundation of a vibrant urban future.
Why Transit Streets Matter
High-quality transit allows a city to grow without slowing down. When prioritized, transit has the potential to stem the growth of vehicle congestion, provide environmentally efficient and responsible transportation, and reduce both personal mobility expenses and overall public infrastructure expenses. And transit that can be relied on makes it possible to build walkable urban places—the kinds of places that city residents increasingly demand.
Accomplishing all of this requires that cities set priorities and make investments, both in transit service itself and in the streets on which transit operates. Much of the transit street design challenge lies in aligning the priorities and demands of city departments with those of transit operators, and in demonstrating the value of investments and dedicated street space to city residents and leaders. Balancing multiple modes in a limited right-of-way calls for a considered approach, with short-term successes building to long-term gains.
Designing to Move People
Transit streets are designed to move people, and should be evaluated in part by their ability to do so. Whether in dense urban cores, on conventional arterials, or along neighborhood spines, transit is the most spatially efficient mode.
Traditional volume measures fail to account for the entirety of functions taking place on urban streets, as well as the social, cultural, and economic activities served by transit, walking, and bicycling. Shifting trips to more efficient travel modes is essential to upgrading the performance of limited street space.
Using person throughput as a primary measure relates the design of a transit street to broader mode shift goals.
While street performance is conventionally measured based on vehicle traffic throughput and speed, measuring the number of people moved on a street—its person throughput and capacity—presents a more complete picture of how a city’s residents and visitors get around. Whether making daily commutes or discretionary trips, city residents will choose the mode that is reliable, convenient, and comfortable.
Transit has the highest capacity for moving people in a constrained space. Where a single travel lane of private vehicle traffic on an urban street might move 600 to 1,600 people per hour (assuming one to two passengers per vehicle and 600 to 800 vehicles per hour), a dedicated bus lane can carry up to 8,000 passengers per hour. A transitway lane can serve up to 25,000 people per hour per travel direction.
Unlocking the enormous potential of transit requires active measures to make trips take less time. To achieve this, the Transit Street Design Guide details street design strategies to improve transit reliability and reduce overall travel times.
Transit service that is reliable and efficient brings value to people and cities, but slow and inconsistent service will discourage passengers and jeopardize local benefits. If a trip takes significantly longer by transit than by other modes, or if actual trip time ranges so widely as to be unpredictable, people may choose not to take transit and cities will miss out on opportunities to reduce congestion and spur development.
For urban transit, getting to a destination faster means removing sources of delay rather than raising top travel speeds. The most significant sources of transit delay are related to both street design and transit operations, calling for coordinated action by transit and street authorities.
TRAFFIC & INTERSECTION DELAY
In mixed traffic, transit is limited by prevailing traffic conditions, and will be delayed by all the factors that delay the cars it shares space with. Time spent waiting for signals or slowing for stop signs, known as intersection delay or traffic control delay, increases as traffic volume nears the capacity of the street, and as cross streets are more frequent or reach their own capacity. Providing transit lanes (see page 110) and using signal strategies (see page 149) can help cut travel times by half, with the greatest benefits made available by using transitways (see page 126). While these levels of priority stop short of grade-separated facilities, they can be the foundation of every city's transit design toolbox, and are inherently adaptable to a variety of street conditions.
While signal delay is relatively easy to address through active TSP if traffic queues are short, signals with long or variable queues can add up to very long delays for buses and streetcars in mixed-traffic conditions. Time spent slowly approaching red signals or stop signs in heavy traffic can also contribute to overall delay.
Unreliable travel times are a major issue for transit operations because short delays can quickly snowball as more passengers try to board a late-arriving vehicle. Missing one green signal can cause a bus or streetcar to fall behind enough to delay the transit vehicle behind it.
Dwell time related to passenger boarding and payment is a large component of total travel time on productive routes, especially in downtowns and destination areas. Level or near-level boarding (see page 64), multi-door boarding and advanced payment options (see page 182), and better passenger information can cut dwell time in half or more. Stop consolidation also reduces the amount of time spent dwelling at stops.
Different transit services call for different facilities. While street design practice has historically focused on motor vehicle movement and has treated transit capacity as primarily influenced by stop design, street design processes are increasingly recognizing that key transit lines—those with higher ridership, higher frequency, and more potential for growth—both need and justify greater accommodation than lower-ridership routes.
Designing for the type and frequency of transit service on a street means providing transit with priority treatments and the space necessary to perform at a high level. Whether a route uses bus, light rail, or streetcar, service decisions in an urban transit network are made based on a complex combination of capacity, reliability, comfort, and the need to accommodate passengers in a network. Some projects involve a simultaneous change in transit service on a street along with transit prioritization or streetscape investments, but all street design projects have a service context.
This section provides designers and planners with a basis of discussion of the needs of transit, by linking specific design elements and comprehensive street designs, found later in the Guide, with concepts of transit service frequency and the type of transit route supported by a street.
Transit Route Types
Different streets, neighborhoods, and cities have different transportation needs, and a wide range of service types are available to meet them. Likewise, service can be complemented by a range of design elements depending on service needs and street context.
When prioritizing street investments, differentiate between “structural” and “non-structural” transit routes. Structural routes form the bones of the transit network, and yield the greatest results from upgrades. Non-structural routes serve to fill gaps in the transit network.
Robust evidence-based service planning using realistic data can identify new service and growth opportunities, especially opportunities to add rapid routes. These can be supported by street design to create broader transit benefits.
Downtown local routes, often frequent, serve an area with a very high demand for short trips and are sometimes operated by a city transportation department or civic group. Unlike conventional loop circulators, downtown locals provide a core transit function for short distances, sometimes parallel to longer local or rapid routes. If planned to complement rather than compete with other structural routes, they can become a permanent feature of the city.
Local routes, whether served by bus or rail, are the basic building blocks of urban transit. Local service must balance access—usually considered in terms of stop frequency—with speed. For passengers and operators alike, reliability is often more important than running time. To be effective, local service must be as direct as possible. Deviating from a direct route to serve areas of relatively low ridership will degrade the quality of service.
With less frequent stops and higher capacity vehicles, rapid (or “limited”) service can provide a trunkline transit service for longer trips and busy lines, or can run along the same route as a local service. Most bus rapid transit, light rail transit, rapid streetcars, and limited-stop bus lines run on this service pattern.
In low-density areas, or where street networks are poorly connected, basic transit accommodation often results in indirect or infrequent service. In these areas, routes have to be circuitous to serve small pockets of ridership. This is best done by using a coverage route rather that adding a deviation to a local route. Keeping coverage routes as direct as is reasonable can be a prelude to a more productive service as density and demand increases.
Provide direct point-to-point service with few stops using limited-access highways, sometimes in dedicated or HOV lanes, to reach destinations quickly. Express bus operation is usually more expensive per passenger than limited service, since it often uses one central boarding/alighting point. Many express services run coach buses.
From Transit Street Design Guide by National Association of City Transportation Officials. Copyright © 2016 National Association of City Transportation Officials. Reproduced by permission of Island Press, Washington, D.C.
The book goes on to cover all of these topics in much greater detail and in a visual, easy-to-digest fashion. Find the NACTO Transit Street Design Guide and other featured books on our publications page. Strong Towns supporting members can receive 30% off.