By Denny Eyler, PE, PTOE

High Occupancy Vehicle (HOV) lanes, High Occupancy Toll (HOT) lanes, and dynamically managed lanes on freeways have proven successful where used in the US. Can a similar lane be added to a surface-divided roadway as a toll lane? It could be described as a Median Reversible At-Grade Toll Lane (MRATL).

A MRATL prototype operated successfully for seven years in Minneapolis, MN. It was a reversible HOV lane built in the median of an at-grade roadway (US 12) and added capacity during the conversion of US 12 to I-394. The design has been unique to date.

This presentation outlines the process for considering a MRATL and the initial steps in developing and evaluating a corridor concept.

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View traffic simulation of US 12 reversible lane

View video of US 12 reversible lane

WHAT IS A MRATL?

A median reversible, at-grade toll lane is a roadway:

  • Located in the median of a surface-divided highway
  • Open during the peak period in the peak direction of travel
  • Runs through traffic signal controlled intersections
  • Where access is usually not permitted at intersections
  • Where entry and exit points are typically located away from intersections
  • Can be a toll and/or an HOV facility and serve as a busway
  • May use grade separations at key locations

WHAT CAN IT DO?

  • Add capacity when the need is of short duration
  • Add capacity when the need is directional
  • Add capacity when funding is limited
  • Improve bus service
  • Add capacity when physical and social constraints rule out a freeway
  • Generate revenue
  • Serve as an interim improvement until the roadway can be converted to a freeway

Criteria for Selecting Candidate Corridors

Traffic Conditions

  • Demand equal to or greater than capacity – critical lane volumes above 1,400
  • High travel times and delays
  • Directional imbalance of 3:2 or greater
  • Peak period greater than two hours
  • ADT greater than 40,000
  • Are there parallel routes that can supply additional demand?
  • Express bus or BRT route
  • Supply of carpools: 2 or 3+
  • Corridor can also serve recreational peaks
  • Agency has existing toll collection system or willing to establish one
  • Ability to use demand-based dynamic pricing
  • Physical Conditions

Physical Conditions

Geometrics

  • Logical termini to collect and disperse added traffic
  • Divided Roadway with median width of 24+ feet
  • If medians are narrow, consider alternative intersection designs
  • Locations for entrance and exits with adequate weaving distances
  • Ideally, no turns permitted to or from MRATL at intersections

Signals

  • Protected only lefts across MRATL
  • Coordination favors MRATL
  • Alternative intersection signals will have alternative phasing
  • Ideally, green time in MRATL lane is nearly equal to open lanes

Evaluating Candidate Corridors

  • Develop peak hour traffic forecasts assuming added toll lane capacity.
  • Check for directional imbalance.
  • Check intersection geometry and median widths. A basic median width of 24 feet or larger is needed between intersections. At intersections, the required width would be dependent on the number of required left turn lanes on the major roadway.
  • Perform planning-level capacity intersection calculations (critical lane). Then, determine toll lane capacity (it should be 700 vph or greater).
  • Check segment termini for capacity issues. There should be available capacity to handle the added traffic reaching the end of the toll segment. If the MRATL terminus is at an interchange, consider adding connections to entrance ramps. If capacity is not sufficient, a signal may be used with priority for the MRATL.
  • At entrance and exit locations, consider weaving issues. Remember you will have a platooned flow environment. Signal control may be required to manage a merge. Try to avoid short left lane drops.
  • Inventory all median openings without existing traffic signal control.
    • Determine which median openings can be closed. Consider a MRATL project as an opportunity to do access management.
    • If median openings cannot be closed, can they have restricted geometry with full or part time signal control?
    • Determine which median openings must remain open and assume signals will be added.

    Consider alternative intersection designs or grade separations when median space is limited or to reduce travel times in the toll lane to meet travel time improvement goals.

    Simulation is recommended to uncover any operational issues. To be considered a candidate for tolling, a travel time savings of one minute per mile in the MRATL should be obtainable.

Operations and Pricing

  • MRATL would typically run inbound during AM hours (6:00 to 11:00) and outbound from 1:00 to 10:00 PM. Time should be available between direction changes to clear disabled vehicles.
  • Hours could be adjusted to serve traffic for other peaks, including weekend recreational peaks or sports events.
  • Toll collection would be done “in motion” using transponders. Toll collection using license plate readers is an option.
  • A dynamic toll algorithm will be needed to ensure demand is managed to maintain good levels of service through the signals in MRATL. Toll pricing will need to be flexible to match local driver’s value of time. Experience has shown that AM peak traffic often needs and accepts higher tolls. For the simulations performed for this presentation, a value for time of $15/hour was used.
  • A performance goal for the toll lane is 30 seconds of time saved per signal passed through or alternatively one minute per mile on the corridor.
  • Allowing HOVs (or “green” vehicles) to use the lane toll free or at reduced cost will be a local decision and affect cost versus benefit considerations and reduce flexibility to manage demand in the lane.
  • Toll revenue is unlikely to cover the entire construction and operating costs of the MRATL. However, the benefits to traffic in the general purpose lanes should be considered in the evaluation and justifying the concept to elected officials.
  • If the roadway system has only some reserve capacity at the termini of the MRATL, then the pricing of the MRATL can be adjusted to control demand to match that capacity.

Technology

The following devices could assist operation of a MRATL:

  • Automated gate operation with manual override
  • Coordinated signal operation with a traffic responsive master control and traffic actuated intersection controllers
  • Full color dynamic message signs
  • Video detection for actuated operation, counting, wrong way or prohibited movements
  • Video surveillance of critical areas such as narrow segments , control gate locations, transit stops and breakdown bays
  • Capability to link toll transponders in the same vehicle for splitting the billing or giving discounts to car pools
  • Emergency vehicle pre-emption with or without access to the toll lane by emergency vehicles
  • Traffic signal to vehicle communication to improve safety and to help minimize stops in the toll lane. End of green warning flashers could also be used.
  • With specific enhancements, toll lane could be used by two way, bus only, traffic during off peak hours by having regularly spaced wide meeting areas, a GPS location system for buses and a transit signaling system to ensure the buses arrive and wait at the passing zones. This would allow the corridor to have a higher form of BRT.
  • Dynamic intersection geometry and signal phasing to reduce conflicting signal phases for the toll lane. Example: change a restricted crossover, U-turn (RCUT) intersection to a U-turn only configuration

Conclusions

  • A MRATL may be a viable option for your corridor
  • Essential elements of geometry and signal control have been developed and demonstrated to perform safely and provide additional peak period capacity as well as being a mobility option
  • Any corridor to be considered will have unique design challenges and they should be fully understood
  • Pricing algorithm needs to be adaptive to local driver behavior
  • Signal coordination should favor the MRATL, but be aware of the possible negative impacts on other traffic
  • MRATL can offer the benefit of improved bus transit in the corridor

Recommendations

  • Have a long-range view of the need for the project and your options
  • Understand existing and forecast traffic
    • Understand the variables in the forecasts
      • Possible changes to the roadway network
  • Future development – how tenuous?
  • How does the preferred alternative meet the project goals
    • Is the project “interim”?
      • A phase on the way to the “ultimate”
      • A temporary fix with its own life-cycle
    • Or will it be the answer for 20 or 30 years?
  • Develop a corridor inventory
  • Do a planning-level intersection capacity analysis
  • For intersections, consider the use of alternative designs – traffic simulation will likely be needed
  • Consider maintenance and enforcement issues
    • Snow plowing and snow removal
    • Toll transponders can assist enforcement
  • Consider signing requirements
    • Don’t build it if you can’t sign it

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