Bus-on-shoulder operations, also known internationally as "bus bypass shoulder" (BBS) operations, are a low-cost strategy allowing buses to travel at or near free-flow speeds through congested arterial and freeway routes. BBS describes the routing of a bus onto the shoulder of a road, usually a highway, in lieu of the standard general-purpose lanes. BBS is a policy-based alternative to constructing dedicated right-of-way or restricting lane use to high-occupancy vehicles (HOV). The primary goal is to prioritize the reliable performance of public transit over capacity for single-occupant vehicles (SOV). It is typically used only where roadway congestion is severe enough that traveling on the shoulder improves on-time reliability and even decreases overall trip time.
BBS techniques are used in limited parts of the United States and examples are found elsewhere in the world . In the United States one of the most extensive networks of bus-only shoulders is found in Minnesota.
BBS can be a successful technique for prioritizing and improving bus transit through areas of severe congestion. The appearance of a bus traveling smoothly past heavy traffic congestion can motivate "choice riders" to switch modes. The reduction of travel time and improved reliability is a powerful motivator.
BBS is a cost-effective strategy for improving transit service travel time and reliability. Because BBS takes advantage of existing freeway space, the costs to implement could be negligible. Some areas have found it important to make improvements to signage or re-stripe lane widths for safety. These costs remain very low compared to removing a lane from general purpose use or constructing a new facility. Agencies could also investigate advanced technologies for bus guidance to improve safe navigation through narrow shoulders.
Another advantage of this strategy is improved access on and off a highway which can speed up passenger stops, especially for express-style service.
If local, regional, or state policy allow, BBS can be very quick to implement. Because there are little to no infrastructure costs, implementation could be as simple as rescheduling and retraining. It may be a challenge to motivate policy makers to allow BBS given its limited use in the United States. Some areas have allowed limited demonstration projects, an example of which is described below.
However, operating any vehicle on the shoulder of a high-speed facility significantly increases risks. As MNDOT notes, the exception is limited to buses, which are driven by highly trained professionals. Shoulders are generally reserved for emergency vehicle access and to provide safe haven for disabled vehicles. While a bus operator should be able to see stopped vehicles well enough in advance to merge into the next lane, circumstances can change quickly leaving the operator fewer options for escape.
Visibility around access ramps can also be a challenge. Older facilities may have very narrow exits or on-ramps making a challenge both for the bus traveling at high speed and other vehicles entering the highway.
In cold climates, the shoulder may be essential for snow storage if it cannot be cleared beyond the paved surface, diminishing the practicality of the bus-on-shoulder service.
Applications in California
A November 2006 newsletter produced by the San Diego Association of Governments (SANDAG) noted that the San Diego Metropolitan Transportation System (SDMTS) Route 960 had been operating a 10-month trial of bus-on-shoulder service. Benefits of the project were 99% on-time performance, high customer satisfaction, and measurable time-savings for commuters. No accidents had been observed in the BBS portion of the service at the time. At the time of this writing, that project had concluded and was discontinued due to new construction on the highway. According to information on the SANDAG website, no other BBS service is operating currently, but SANDAG and SDMTS are working to develop a new BBS service elsewhere.