Where are single-lane busways proposed?

The Better BRT plan recommends three or four segments of single-lane busway, as outlined in the table below.

The types of busways listed in the table are explained further below, but first we’ll explain why it’s not necessary to have two bus lanes on Route 29.

Why single-lane busways could work on Route 29

Due to the jobs-housing imbalance along the Route 29 corridor, traffic is also imbalanced, meaning that traffic jams on most of Route 29 generally only occur in the peak direction. During the morning rush hour, southbound traffic is heavy and there is essentially no northbound traffic. The opposite is true during the afternoon rush hour.

Because congestion only occurs in one direction at a time, it is not necessary to have a dedicated lane in each direction. Only one dedicated lane is needed for buses to bypass traffic in the peak direction; buses going in the non-peak direction could operate in mixed traffic without delays. Therefore, a single-lane busway on Route 29 would provide nearly the same level of reliability and travel time savings as two dedicated lanes, but at half the cost and using half the space.

That being said, based on the geometry of the corridor and the unique station design of the Better BRT plan, it may be possible to have buses in both directions share the single-lane busway segments to maximize the system reliability. This layout is called a bidirectional busway and is described in more detail below.

Types of single-lane busways

There are several options for implementing a single-lane dedicated busway. The three that are considered in the Better BRT plan are presented below.

Bidirectional median busway

A bidirectional busway involves buses travelling in both directions using the single lane segment throughout the day. The process would resemble single tracking on a rail line, but without the inefficiencies, delays, and frustration. Bidirectional busways are appropriate for relatively short segments (1 mile or less) with few traffic signals, and where buses cam travel moderate speeds (30 mph or greater).

The most well-known example of a bidirectional busway is the Emerald Express (EmX) in Eugene, Oregon. Most of the EmX Franklin Line was built using a single-lane bidirectional configuration due to site constraints. The EmX uses an advanced traffic signaling system to schedule buses so they can take turns sharing the bidirectional lane without conflicts. The system was also designed with busway breaks at key points to allow buses to pass each other.

The Better BRT plan recommends a bidirectional busway for Segments 2 and 3. Each of these single-lane busway segments is about one mile long. A bus travelling at an average speed of 20-30 miles per hour could clear each segment in three minutes or less. Even if buses in both directions are operating at 7.5 minute headways (7.5 minutes between each bus), there is still plenty of buffer time between opposing buses.

Bidirectional busways are nearly always placed in the median. In order for a bidirectional segment to function correctly, areas for buses to pass each other must be provided at each end, usually in the form of stations. The Better BRT plan provides the following locations near the end of each bidirectional busway for the buses to pass each other:

• North of New Hampshire, where the single-lane busway becomes a two-lane busway
• In Burnt Mills: at the proposed BRT station on Lockwood Drive
• In Four Corners: either at the station or in the two-lane busway between University Boulevard and Timberwood Avenue.

The video below illustrates how Segment 3 could operate as a bidirectional busway between the Four Corners and Burnt Mills stations.

The figure below illustrates how Segment 2 could operate as a bidirectional busway between the Burnt Mills station and Stewart Lane.

Reversible busways

Reversible busways are similar to a bidirectional lane, but only the buses travelling in the peak direction would use the dedicated lane. Buses travelling in the off-peak direction would run in mixed traffic.  This allows buses to bypass the most congested lanes in the peak direction during rush hour. Reversible busways are appropriate only on roads with significant peak direction imbalances; as mentioned above, most of Route 29 between the Capital Beltway and Howard County falls into this category.

Reversible busways can be placed in the median or curbside (right lane). Median busways are generally more effective, because they are separated from nearly all general traffic. The capacity, reliability, and performance of curbside busways can be hampered by vehicles obstructing the right lane, such as right-turning vehicles, conventional buses, stopped taxis and cars, delivery vehicles, garbage collectors, and mail trucks. Median busways on the other hand, are only affected by left-turning vehicles (the solution to avoiding those conflicts is explained here).

The Better BRT plan recommends that Segment 5, from the Capital Beltway to Sligo Creek Parkway be a reversible median busway as opposed to a bidirectional busway because there is extremely limited area south of Sligo Creek Parkway to accommodate a bus passing area.

Curbside reversible busways can use a contraflow configuration or rush-hour-only exclusive lanes. In a contraflow system, the bus lane doesn’t move and could therefore be on the “wrong side” of the road depending on the time of day. This is not recommended due to safety concerns. On the other hand, with a rush-hour-only exclusive lane system, the right-most lane in the peak direction becomes an exclusive bus lane during morning rush hour and switches during the afternoon. This could potentially be implemented on Route 29 as described below.

Reversible dedicated lanes could be extended to Georgia Avenue

An optional feature of the Better BRT plan is to provide a reversible curbside busway (also referred to as peak-hour-only exclusive lanes) on Segment #6, from Sligo Creek Parkway to Georgia Avenue. A median busway cannot be used for this segment because site constraints force the stations on Fenton Street to be on the curb. Additionally, the middle two lanes of this stretch are currently reversed every day to accommodate traffic in the peak direction during rush hour. Peak-hour-only exclusive lanes would allow buses to skip the heavy congestion entering and exiting downtown Silver Spring, but it would require repurposing of a general purpose lane, which could significantly delay other road users during rush hour.

Other considerations

In order for a bidirectional lane to function reliably, the segment travel time must be less than half of the headway time (time between bus arrivals) so that the buses can pass each other on schedule. Variables can affect bus speed through the segment, particularly traffic signals. The Better BRT plan calls for adding new signals to facilitate access to and from neighborhood side streets and prevent conflicts between turning vehicles and buses. Some are in areas with a single-lane busway segment. All new and existing signals would be outfitted with transit signal priority (TSP) as part of the plan so that traffic signal bus delays could be minimized.

If engineering analysis determines that the benefits of bidirectional busways for Segments 2 and 3 are outweighed by costs, risks, or other factors, a reversible busway configuration in the median could be used instead, without significant changes to the Better BRT plan. In that case, buses in both directions would still use the two-lane busway at Four Corners to pick up/drop off passengers, but the off-peak buses would merge out of the busway and into mixed traffic near Timberwood Avenue and the Capital Beltway overpass. During non-peak periods, the reversible busway could be assigned to a certain direction based on need at the time.

Further Reading

More information about reversible and bidirectional busways is available on the following websites:

• American Public Transportation Association (2010). Designing Bus Rapid Transit Running Ways.
• Transit Cooperative Research Program (2010). Bus and Rail Transit Preferential Treatments in Mixed Traffic.
• Lane County Transit District (2008). Lane Transit District’s EmX Project. Presentation of the BRT system in Eugene, Oregon.
• Institute for Transportation and Development Policy (2017). BRT Planning Guide, Roadway and Station Configurations.