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Top 6 Ways Separation Strategies Can Impact Managed Lanes Operations

By Michael Davis, PE, DBIA

November 30, 2015


With the increased deployment of Priced Managed Lanes (PML), we have been able to better understand the advantages, disadvantages, and impacts of lane separation techniques. There are many factors that affect the type of separation to be used between the PML and the General Purpose Lanes (GPL).

  1. Safety – Safety items to consider are: incident avoidance, incident management, and lane clearance
  2. Right-of-Way – Some separation types require more right-of-way due to the need for more shoulder room in addition to the space needed for the device placement.
  3. Cost – Some separation types cost more for initial installation. Cost can also be associated with the need to maintain/replace devices and should be included in any analysis. The flexible/tubular delineators tend to be the most maintenance needy type since they tend to get dislodged by errant vehicles.
  4. PML Roadway Characteristics – The way the PML is designed to operate impacts the separation type used. PML operation could be identified as one of the following:
    • Reversible – Lanes operate directionally based upon the peak direction of traffic. This operation always requires the use of barriers to separate the PML from the GPL.
    • Concurrent flow – Lanes operate in the same direction as the GPL for both directions of traffic.
    • Elevated – Lanes operate at a different level than the GPL.
    • Mixed mode – Lanes operate differently depending on the time of day and traffic needs. For instance, during peak times the lanes would operate as PML with HOV restrictions and tolled vehicles, but off peak the lanes would not have any HOV requirements.
  5. PML Operational Characteristics – The restrictions or requirements to vehicles that use the PML and how the lanes will be tolled can impact the separation type used. Controlling factors are:
    • Vehicle Occupancy –This would impact the need for additional enforcement needs to verify vehicle occupancy.
    • Vehicle Type – With large trucks, lane widths allowed will be impacted. This in turn can affect the PML footprint and the ability to use certain types of separation in existing cross sections.
    • Dynamic Price Tolling – If this type of pricing is used, access to/from the PML is crucial since this will determine how pricing is established and how the lane use is regulated. With barriers, this type of system is controlled by the physical separation. With delineators or pavement markings, the control is in additional detection devices and enforcement.
  6. Access Points – The type of access and the number of access points can impact the separation type used. Whether there are multiple access points to/from the GPL, minimal access points to/from the GPL, or direct access to/from crossroads, this has an effect on the interaction between PML and GPL vehicles and how the merging between them will occur. It also affects the length of opening needed in the separation types used since barriers require crash attenuators on their blunt ends, while delineators and pavement markings are more forgiving.

Topics: Insights, Transportation, Tolls & Managed Lanes, Transportation Industry News

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About the Author

Mike serves as the Tolls Service Group Leader for RS&H and has more than 22 years of experience in the transportation industry, including 15 years dedicated to managed lanes and tolling. During his diverse career, he has helped manage the development of managed lanes systems throughout the United States, including Florida, Georgia, Virginia, and California.

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