Don’t get your buses in a bunch.

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Modern transit agencies are continually challenged to improve the efficiency of their operations. It is often a challenging balancing act to minimize passenger wait times while maintaining an efficient passenger load. If vehicles run too closely together, passenger wait times and the efficiency of passenger loads will suffer.

Despite the best intentions of transit operators, the bunching of vehicles (buses or shuttles) occurs when two or more vehicles operate on a route, in the same location, at the same time. Also known as clumping, platooning, or convoying, there are numerous contributing factors in bunching—many of which are unavoidable, such as:

  • Traffic congestion
  • Construction delays and detours
  • Varying passenger loads
  • Driver behavior

Rather than arriving at a destination at regularly spaced intervals, vehicles on the same assigned route arrive at the same time (or very close together). This has the effect of providing unreliable service for riders in the form of longer wait times and overcrowded vehicles than would normally be present had the schedule been followed.

From an operational standpoint, the impacts of bunching can be just as inconvenient to the agency as it is to the rider:

  • Poor schedule performance
  • Higher rate of inbound calls
  • Customer complaints
  • Overbalanced passenger loads

Needless to say, solving the bunching problem is a pressing issue among transit agencies and the vendors who provide intelligent transit systems.

Here are some ways to mitigate the risk:

Use a real-time ITS to adjust to operating conditions.

Modern intelligent transit systems use GPS to proactively help identify potential bunching scenarios by providing real-time updates on vehicle locations, allowing agencies the opportunity to adjust the pacing of vehicles before a situation emerges.

  • Use real-time assessments to improve operational awareness and provide transit agencies with timely information concerning current operating conditions so that the operator can make meaningful, real-time decisions.
  • Utilize live vehicle tracking, or a combination of bus tracking technologies and control center software to provide visual cues to highlight potential issues and resolve them.

Some ITS vendors go beyond simple GPS tracking and provide real-time anti-bunching technology using a dispatch-free approach. This allows drivers to easily make on-the-fly adjustments to increase spacing between all vehicles. This is typically implemented through on-board graphical interfaces that provide drivers with information concerning bus spacing such as:

The locations of buses adjacent buses on the same route

  • A sliding scale to reflect relative distance between the vehicle’s neighbors
  • An immediately, recognizable color scheme to advise the driver of their spacing status

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By providing the driver with a minimalist interface with no requirement for interaction, anti-bunching systems present enough information to allow drivers to easily understand their position on the route as well as provide guidance to increase the smoothness and efficiency of the run.

The highly visible color scheme makes it immediately apparent to the driver when vehicle bunches are beginning to form around their vehicle.

The challenge present in any anti-bunching solution is the identification of a bunch as it forms, and selecting the most efficient resolution to dissolve the bunch, and communicating that information to the driver.

Adaptive algorithms are used to adaptively identify bunches under various conditions, such as:

  • The length of the route and the number of vehicles currently running the route
  • The density of stops along the route
  • The length of stretches of “open road” where there are no riders to pick up (such as lengths of travel along interstates and freeways)

Dissolving bunches is the next challenge. This problem requires the consideration of numerous solutions for smoothing while prioritizing the corrective action based on a number of considerations, including traffic laws and passenger safety. Each profile is given a score and the result determines the corrective action that is presented to the driver.

These systems can also be configured to reduce or broaden the “green zone” around each vehicle that keeps the system from providing a constant flow of corrections and only alerts the driver when intervention is required.

Use digital communications to keep riders in the loop.

The simple truth is that any approach to mitigating the bunching problem does have an impact on the riders. In many cases, this reality can largely be negated by providing customers with numerous ways to stay current with any potential delays and allow riders to make adjustments to their schedule prior to arriving at a transit stop.


Simply providing communication tools to the riders can improve the perception of quality and actually improve and agency’s reputation as one that proactively informs its customers and actively works to minimize impacts of situations largely beyond its control. An always-on communication system allows for drivers and dispatchers to seamlessly identify and resolve issues quickly and efficiently, and push notifications to riders via digital signage, public websites, PA announcements, and smartphone applications.

What does this mean for transit operators?

Transit agencies must make informed decisions about the technologies in which they invest to provide these intelligent services. It is always an expense to invest in new systems, so having an understanding of the associated short-term and long-term costs (in both hardware and manpower) is important.

As technologies evolve, it is easy for a transit agency to fall behind in addressing issues like bunching because the cost of upgrading its legacy systems often prove to be cost prohibitive, and piecing together multiple solutions can lead to compatibility and reliability issues.

The battle of the bunch.

The simple truth is that the fight against bus bunching is an on-going issue and no one solution or vendor has developed that magical solution that sends the problem into the history books. What matters is that transit agencies DO something. Every effort helps mitigate the problem, and whether the solution that works best for your agency is decidedly high-tech or deceptively low-tech, if it helps improve rider satisfaction and overall performance, it’s worth it.