Development of Operational Performance Models for Bus Lane Preferential Treatments
Bus lane preferential treatment gives preference to or priority for buses to use certain lanes on an arterial street or a freeway. The objective is to improve bus services by reducing bus travel times and increasing service reliability. Typically, buses share the same streets with other vehicles and receive no preferential treatment, thus suffer from traffic congestion. More and more cities have built special roadways or designated special lanes for buses, which are called busways or transitways. Because buses use little capacity, it is common to also allow vanpools and carpools to use the lanes, which are then called high-occupancy vehicle (HOV) lanes. In general, buses running on facilities that give them preferential treatments are referred to as Bus Rapid Transit (BRT).
Because BRT combines the quality of rail transit and the flexibility of buses, it has received increasing emphasis by the Federal Transit Administration (FTA). Last year the FTA funded 10 bus rapid transit demonstration projects around the country with the primary goal of working with a group of localities in demonstrating approaches for increasing the level and quality of bus service in major investment corridors. Extension of the existing South Miami-Dade Busway is one of the funded projects.
A variety of BRT systems exists. Some use one lane; others use two lanes operating in the same direction; still others use two lanes with bi-directional flow. Some use the curb lane; others use the left-side lane. Some restrict vanpools and carpools to only the second HOV lane; others do not. Sometimes the lanes are restricted only in peak periods; others operate 24 hours a day. With the many possible design alternatives comes the need to identify the best-suited alternatives for implementation. Making the right decision is extremely important because preferential facilities are costly to build, maintain and enforce, and because they impact not only buses but also other vehicles. The decision-making process requires a good estimate of the operational performance of all candidate preferential treatments.
The operational performance, which may be measured in travel time, speed, capacity, etc., cannot be easily estimated. It is affected by a number of factors, including bus headway, vehicle volume, vehicle mix, dwell time, bus stop location, bus stop spacing, bus stop type (online or offline), flow speed, signal control strategy, number of lanes, etc. Accordingly, the development of quantitative models that relate a performance measure to its contributing factors would be the logical approach to fulfilling the need. Such models do not currently exist.
With such models, proposed preferential treatments can be evaluated before implementation, existing treatments can be re-evaluated for possible improvements, and should a treatment become controversial, it can be defended objectively. In addition, because such models include a number of design variables, they can be used as a design tool to evaluate the effectiveness of a design alternative, for example, the location (near side, far side, or mid-block) of bus stops.
This project aims to develop operational performance models that can be applied by transit planners and traffic engineers to help determine the appropriate bus lane preferential treatments. The execution of this project is in line with the increasing interest in implementing BRT systems at both the state and the federal levels.