Transit priority

"Transit priority" and "transit first" refer to policies that promote the use of transit, walking, bicycling, and sometimes taxis and shared-ride services over private automobile travel. Changes made to street design and infrastructure under transit-priority policies range from installing signal priority (a less involved "spot" treatment) to implementing separated bus-only lanes (an extensive, corridor-level treatment). All these policies share the goal of elevating shared modes of travel to a level of convenience that parallels driving, especially in corridors in which automobiles exact high externalities on non-drivers (e.g., busy urban avenues where buses tend to get stuck behind private-vehicle traffic).

Benefits of Transit Priority

Unlike major capital improvements, which are popular with voters but also very expensive and involved, transit-priority policies are relatively easy and cheap to implement. They can be tailored so that they are highly responsive to the concrete, demonstrated needs of riders (i.e., installed at "pinch points" where traffic is especially bad or where transit vehicles encounter major delays). Research shows that even small increases in vehicle speed and reliability can pay off with significant ridership gains.

Transit Priority Techniques

Bus-Only Lanes

Bus-only lanes can increase the ease of access, reliability and appeal of transit service particularly within dense, congested areas. In recent years, cities have experimented with painting bus-only lanes to further distinguish the lanes for exclusive transit use and to elevate awareness of transit generally. Bus-only lanes are commonly used in BRT projects, but also exist in other applications such as transit corridors, and queue jumpers.

Bus-only lanes can be full-time or have hours of operation (e.g., during peak hours). Some allow taxis and/or bicycles; others are exclusive to transit vehicles and right-turning vehicles. Commonly, bus-only lanes are curbside, which necessitates their sharing intersection-adjacent space with right-turning vehicles, which can add significant congestion and transit vehicle delay, particularly where turning vehicles in front of transit vehicles must wait for crossing pedestrians. Median bus-only lanes are rarer as they require boarding islands, but have the advantage of eliminating traffic conflicts and maintaining lane exclusivity for transit vehicles. Contraflow bus lanes are rarer still, and involve a transit-only lane on a one-way street, with transit vehicles running in the opposite direction as traffic.

Header text	Benefits	Challenges	Remediations
Curbside Lanes	No extra space needed for stops	Often congested due to illegal parking/waiting and right-turning vehicles	Use curb lane for parking/turns and adjacent lane for bus only; use automated enforcement; reserve spots for deliveries; restrict delivery hours
Median Lanes	Less likely to be congested than curbside lanes	Requires more space for platforms Lanes conflict with left-turning traffic Pedestrians must cross traffic to reach platform	Ban left turns or create separate signal phase
Contraflow Lanes	Lanes are “self-enforcing”; Violations are rare and easy to spot	Prevents use of curb for deliveries	Reserve curb lane for deliveries and use next lane over for transit

Transit Signal Priority

TSP involves programming traffic signals to be actively responsive to transit vehicle movement, allowing transit vehicles to pass through the corridor more quickly than they otherwise would. While TSP can be used with bus-only lanes for greater effectiveness, it can also be implemented on its own where bus-only lanes are infeasible or not yet developed.

TSP strategies include extending green lights for approaching transit vehicles (detected through in-pavement sensors and/or through on-board transponders), making red lights shorter for waiting transit vehicles, and adding or changing traffic signal phases to favor transit vehicle movement. Some TSP systems can be developed to use a context-specific algorithm to determine when and how long to trigger a TSP request, such as the individual transit vehicle’s schedule adherence, which improves TSP performance 3-6%. Theoretically, TSP algorithms could also be set to consider passenger occupancy, as well. TSP benefits do, however, diminish with higher volume/capacity ratios.

Other Transit Priority Tools

Queue jumps refer to a specific type of transit signal priority used at signalized intersections that gives transit vehicles a special signal to “jump ahead” before other traffic gets a green light. Queue jumps typically are installed where a bus has its own lane (or bus bay stop) at the near side of the intersection, but not the far side. They are, essentially, very short bus-only lanes with a single TSP installation. The “head start” that queue jumps give transit vehicles obviates the need for them to merge with traffic and helps keep them on schedule.

Typically stretched over a couple blocks, transit malls constitute urban space given over primarily to transit service. They have exclusive transit only lanes and are sometimes closed to all vehicle traffic. Importantly, they are designed around easy and safe pedestrian access and are usually retail or mixed-use areas. Among the best known examples is Nicollet Mall in Minneapolis, the first transit mall in the U.S., constructed in 1967.

Transit corridors are streets in dense, urban areas in which a public investment in transit service is visibly established even in the absence of transit vehicles. Often, transit corridors have an improved streetscape amenable to pedestrians, enhanced street furniture particularly at bus stops, bicycle facilities, and restrictions on curbside parking. Some have part-time or even full-time bus-only lanes. Frequent, high-quality transit service serves the corridor. While transit corridors can have much in common with transit malls (pedestrian-friendly environment, bus-only lanes) and with BRT (frequent transit service, TSP), they are typically longer than malls and shorter than BRT routes.