New study examines how bus and bicycling travel times interact in stressful street networks
As cities move forward with ambitious plans to revamp bus services and add dedicated bike infrastructure, which in turn will help draw riders and bicyclists, the level of comfort in nearby streets still play a large role. Streets free of the stress from dangerous, fast-moving traffic can not only support bicycling, but also expand the accessibility of nearby transit stops.
For planners, the solution is to create a network of roads with moderate traffic, fast enough for buses but comfortable enough to encourage bikes and pedestrians. So concludes a new report, “Improving Livability Using Green and Active Modes,” from the Mineta Transportation Institute. “Our study looks at a classic trade-off between livability and mobility as it relates to green and active modes, specifically between bicycling and transit service,” explains Dr. Bruce Appleyard of the San Diego State University School of Public Affairs, one of the report’s authors.
The research relied on detailed information about specific cities, neighborhoods, and streets, including their “transit travel times, frequency of service, and access networks.” The authors used a 2012 model, “Low Stress Bicycle Network Modeling,” also developed by the Mineta Institute, to compute the study areas’ Level of Traffic Stress, or LTS.
The scale of levels begins with LTS 1, which is generally too slow for bus and other traffic, and goes as high as 4, with crowded, speeding traffic in multiple lanes, which only a few fanatical bicyclists will brave. LTS 2 proves ideal for modes that mix biking or walking with buses, as well as for entirely non-motorized trips. The main conclusion is that a street network should maintain a LTS 2 to encourage bicycling and walking in a mixed-mode environment.
Levels of street stress mapped in Denver, Colo., show low-stress neighborhoods separated by thoroughfares. Source: MTI.
Importantly, the report shows how high-stress streets make it hard to access transit, while low-stress streets create larger catchment areas for pedestrians and bicyclists. In other words, networks of LTS 2 or LTS 1 streets support higher bus ridership, because they allow people to bike or walk to stops. Of course, LTS 1 is too slow for most bus service, making LTS 2 ideal for all modes.
While less appropriate for children on bikes, LTS 2 appeals to the majority of bicyclists and potential bicyclists while creating a safe, pleasant walking environment. An LTS 2 road is one where “cyclists are either physically separated from traffic or are in an exclusive bicycling zone next to a well-confined traffic stream … or are on a shared road where they interact with only occasional motor vehicles with a low-speed differential.” Turn lanes are configured to give bicycles priority, and safe street crossing are available for pedestrians. Depending on conditions, car speeds should top out at around 30 mph – which, in practice, means a posted speed of 20 or 25 mph – and street width should be limited to two or three lanes.
Along with achieving LTS 2, the report suggests other enhancements to encourage walking and biking, including connectivity, effective transit, and accessible stations. Specifically, the report recommends “transit-only lanes, transit priority lanes at the intersections, transit-stop bulb-outs, and integrated networks of pedestrian and bicycle routes.”
The idea is to create a network that will appeal to “interested but concerned” bicyclists, that large group who would bike to work if only it weren’t so difficult and dangerous. As the report puts it, “The single most important factor for bicycle travel is safety.” Creating a safe and comfortable biking environment would draw out more women riders, as well as younger and older people, conditions that currently exist in Denmark and the Netherlands. In the United States, by contrast, the much smaller number of bicyclists consists largely of young men.
Separated bike lanes are an additional improvement, one strongly encouraged by bicycle advocacy groups, that can help create safe, bikeable networks. Explains Appleyard, “Creating separated bike paths that would increase comfort for cyclists through greater separation from traffic, would be an effective solution for improving Level of Traffic Stress.”
The caveat to such improvements is that making a street network safe and inviting for bicycles means some ridership competition with buses, as it will often be as fast simply to bike. Since buses and bikes both maintain a speed of around 12 mph, she who begins a trip on a bike might choose to stay on a bike, if conditions permit.
As Appleyard puts it, “lower levels of traffic stress (LTS 1 or 2) make the choice between a bicycling/bus transit and bicycle-only modes become equally attractive and substitutable.” He adds that, “There are health benefits to consider, as well as a bicyclist’s sense of independence.” (It is, however, important to maintain bus service as an alternative mode when bad weather makes bicycling difficult or impossible.)
The street network along a bus route in Denver, if one considers all streets up to LTS 3. The report explains that differing colors near bus stops mean either the “stop may not be used because it is not connected at that level, or its travel time is more than another accessible stop at that access speed.” Source: MTI.
The report examines the cities of Denver, Colorado and Oakland, Calif., in detail. It finds a majority of streets to be LTS 1 or 2 in both cities, with Denver particularly navigable by bike, possessing a whopping 81 percent of LTS 1 roads. The problem comes with main thoroughfares at LTS 3 and 4, which block access to other streets, fragmenting networks.
While the report concentrates on buses as a public transit mode, higher speed transit is available, including rail and bus rapid transit. In such cases, people are willing to travel a greater distance to access transit, greatly increasing coverage area. Future research is needed for such situations, but this report lays the foundation.
As Appleyard puts it, “policymakers can make choices that work for all modes. It is important, however, that they consider the needs of these modes comprehensively.” “Improving Livability Using Green and Active Modes” offers an important lesson for decisionmakers wishing to design a pleasant, multimodal city in which low-stress streets support multiple non-driving options comfortably.
Photo, top: An ART bus and a bicyclist share the street in Arlington County, Va. (Sam Kittner for Mobility Lab, www.kittner.com).