Roles of Transportation Management Centers in Incident Management on Managed Lanes
Chapter 2-Unique Aspects of TIM in Managed Lanes
Many of these topics are familiar to transportation and emergency response professionals. This guidebook links these topics together. This chapter will examine how TIM using a TMC in managed lanes is different than typical freeway TIM, which is a critical component to understanding the best practices that will be presented later in the guidebook.
On most transportation corridors under the jurisdiction of a TMC, there is one transportation agency responsible for operation and maintenance of the entire corridor. However some managed lane facilities are operated by a different agency than the adjacent general purpose lanes. This will require coordination between the two agencies for normal operations and during incidents.
Figure 15. Photo. Express Lanes in Orange County, CA are operated by a different agency than the adjacent general purpose lanes.
The agency that ultimately operates a managed lane facility depends on many factors, including when the facility was constructed, if the facility was purpose-built or converted from another use, funding constraints, and the operating authority of the various transportation agencies in a metropolitan area.
Typically, one of three types of agencies operate managed lanes:
Having more than one transportation agency or operator responsible for roadways co-existing in a single right-of-way is unique to the managed lane environment. In some cases, the two operators' jurisdictions are separated by only a few feet of pavement with a very simple barrier between the two, if any. The result of this physical configuration is a high likelihood of interaction between the general purpose lanes and the managed lanes during normal operations, maintenance, and incidents. Maintenance activities must be closely coordinated to ensure adequate operation of the transportation corridor and that two agencies are not competing for the same roadway space for their respective activities. An incident on one facility may be detected by the other facility's operator. Additionally, an incident on one facility can quickly affect operation of the other facility. The barrier between the two facilities may be breached during the incident, and the barrier may need to be crossed by responders and diverted traffic.
All of the above scenarios will result in the need for close coordination between the operator of the general purpose lanes and the operator of the managed lanes if the two facilities are not operated by one agency.
Managed lanes usually have more ITS assets and TMC functionality than a typical freeway. Managed lanes are designed to allow proactive implementation of management strategies in response to changing traffic conditions. In order for this to occur, ITS assets must be able to detect when traffic conditions change to require a response from the operating agency. This will generally require a more robust deployment of ITS assets that can detect incidents than are found on a typical freeway. In some cases, the entire managed lane facility is within the range of a Closed Circuit Television (CCTV) camera. An agency in charge of operating a managed lane facility is generally willing to provide enhanced ITS and TMC functionality in order to ensure the success of the facility.
Figure 16. Photo. Managed lanes typically have extensive deployments of ITS equipment, such as these CCTV cameras.
Examples of enhanced ITS assets and TMC functionality that can be found on many managed lane facilities include:
The enhanced capabilities of the TMC allow for better detection, verification, response, and clearance of incidents that occur along the corridor. This will result in incidents being cleared faster and subsequently less downtime for the managed lanes.
Some managed lane facilities have traffic control tools that can be activated from the TMC to support TIM. Managed lane facilities are more likely to have these capabilities than other freeway facilities.
Figure 17. Photo. Some managed lanes can be remotely closed from the TMC, such as this reversible facility.
Some examples of control strategies that can be implemented from the TMC include:
Variable speed signing
Some managed lane facilities have changeable speed signs along the facility. These signs can be adjusted from the TMC to reduce the speed limit approaching an incident zone. Depending on the laws of the area where the managed lane is located, this variable speed may be advisory in nature or it may be an enforceable speed limit. In states where both an enforceable speed limit and an advisory speed are both permitted, the choice of which type should depend on the ability to effectively enforce the limit. An advisory speed may be more suitable for areas where police enforcement is not practical. The use of variable speed signing can encourage drivers to slow down when approaching a TIM zone, and thereby reduce the likelihood of injuries to responders, secondary crashes, and reduce the severity of any crashes that do occur in the incident management zone. An enforceable variable speed limit must be supported by state law, and driver compliance may vary depending on the level of enforcement normally associated with the managed lane facility. When an enforceable speed limit or advisory speed is used in combination with DMS messages warning drivers of an incident ahead, the reduced speed may be more effective as drivers will understand the need to slow down.
Figure 18. Illustration. MUTCD sign showing variable speed limits.
Lane control signals
These are the green arrow and red "X" signals that appear over lanes. Some managed lane facilities have lane control signals that can be used to remotely close and re-open lanes from the TMC. These signals can be used in the course of normal operations to open or close lanes, control entry to access points, and assist with switching direction of reversible facilities. Regardless of whether or not signals are used in the course of normal operations, available signals can be a handy traffic control tool during incidents. This will improve incident zone safety by directing vehicles out of the blocked lane prior to the incident, and can reduce backups by allowing traffic to merge when gaps are available rather than being forced to merge at the incident. Lane control signals will also allow lane closures to be implemented much faster than if the signals were not available.
Effectiveness of Lane Control Signals
Experience in some areas shows that the effectiveness of lane control signals is limited due to aggressive driver behavior and distracted drivers. While lane control signals can be used as a tool to manage traffic at an incident scene, the most effective way to establish an incident scene is with service patrol trucks and emergency vehicles. The greatest compliance with posted lane control signals occurs in free-flow, high-speed conditions.
In order to achieve increased rates of driver compliance with lane control signals, they must be deployed quickly and accurately, which requires a high level of attention from the TMC operator in addition to quick and accurate detection and verification of the incident's location.
Managed lane facilities that have a zipper barrier can have the barrier moved to open or close lanes, allow for diversions, or allow emergency responders to reach an incident. The zipper barrier must generally be moved by a ground vehicle, and TMC staff can direct ground crews to move the barrier if needed.
Many managed lane facilities have some form of DMS units, signals, or gates at the entrances to managed lane facilities that could be used to completely close the managed lane facility to traffic from the TMC. This is a tool that can be implemented if a serious incident blocks all lanes, an incident is expected to be long in duration, or the impact to traffic will be high. Implementing a full closure of the managed lanes may be necessary to prevent severe traffic backups behind the incident or prevent vehicles from becoming "trapped" behind the incident. The closure can be implemented using signs dedicated to providing the open/closed status or by utilizing other signs normally used for other purposes, including the signs listing the toll rate for priced managed lanes. In such cases, the signs could be changed to display "closed" rather than a price. Although a facility closure may not prevent all vehicles from becoming trapped behind an incident, if some vehicles can be directed away from the incident scene, the response to the incident will be improved.
A diversion can be implemented in one of two directions: general traffic can be diverted into the managed lanes, or managed lane traffic can be diverted into the general purpose lanes. A diversion is similar to a facility closure, though it is usually implemented by diverting vehicles already in the facility off of it at an intermediate location rather than simply preventing vehicles from entering at defined entry points. If traffic is diverted off at a defined exit point, DMSs can be used to the extent possible to guide vehicles onto the exit ramp. If a diversion is implemented at an intermediate point, responder assistance on the ground may be necessary to direct vehicles into the diversion and to remove any physical barriers that may exist. This effort can be supported by the TMC by activation of the DMSs to warn drivers of the diversion, closure of any entry points downstream from the diversion, and suspending automatic enforcement of regulations that are not applicable during a diversion, such as "invisible barriers".
Adjusting toll rates
Priced managed lanes with dynamically adjustable toll rates can increase the price for use of the managed lanes in order to discourage all but the highest value trips from utilizing the facility. The ability to adjust toll rates may be limited by the managed lane facility's operating procedures. For example, some facilities have an upper limit on the tolls, and others adjust toll rates on a set schedule, and the ability to deviate from that may not be permitted. Other toll facilities adjust toll rates depending on traffic conditions to maintain certain minimum operating conditions, such as a 45 MPH travel speed. In some priced managed lanes, the algorithms which determine the toll price under normal circumstances can be overridden by TMC staff in the case of an incident to reduce the number of vehicles entering the managed lanes. This TIM tool may be useful where a full closure or diversion is not necessary, but a reduction in traffic volumes in the managed lanes is necessary to preserve the operating conditions in the lanes for high priority traffic such as transit vehicles. Careful consideration needs to be given to how drivers react to the toll rates displayed on the signs before relying on this as a TIM strategy. For example, on some facilities, increasing the toll rate may lead to an increase in vehicles entering the managed lanes, since drivers will mistakenly believe that a high price means traffic conditions are poor in the general purpose lanes.
Adjusting vehicle eligibility requirements
This tool is similar to the adjustment of toll rates in that the goal is to reduce the demand on the facility. An existing vehicle occupancy requirement can be increased, an eligibility requirement could be implemented where none normally exists, or a HOT facility could suspend access for those paying tolls and restrict entry to HOVs only. This TIM strategy will typically be implemented by adjusting electronic signs at the entry points to the lanes, and could be constrained by state or local laws. For example, the operating agency may not have the authority to change the occupancy requirement from two person carpools to three person carpools, but may have the authority to deny access to single occupant toll-paying vehicles if the two person HOV definition is not changed, thus granting priority to HOVs. An alternative could be to restrict access to buses or other transit vehicles only, and disallow general traffic. The implementation of a vehicle eligibility requirement change will reduce demand on the HOV facility while preserving access for the highest priority vehicles carrying the most people.
Figure 19. Photo. Managed lanes can suspend all eligibility requirements and allow all traffic.
Suspension of eligibility requirements
This TIM strategy will open the managed lanes to all traffic and is typically implemented in response to an incident in the general purpose lanes where the managed lanes are needed for diversion. Implementing a suspension of all eligibility requirements is generally not seen as a desirable TIM strategy, as priority access for eligible vehicles in the managed lanes is not maintained. However in some circumstances, there may be no suitable alternative to safely and effectively handle traffic from the general purpose lanes other than opening the managed lanes to all traffic. This TIM strategy can be implemented from the TMC by displaying detour information on electronic signs approaching the lanes, and suspending enforcement of tolls and occupancy requirements.
Managed lanes are more likely to operate in a physically constrained environment than a typical freeway segment. The physical layout of the managed lane facility will impact the TMC's ability to perform TIM tasks during an incident, including allowing responder access to the managed lanes and the ability to implement a diversion. Section 1.3 of this guidebook discussed various physical layouts for managed lanes. The type of barrier and the lateral clearance between the travel lanes and barrier are factors in the amount of access constraint there is during an incident.
There are three levels of physical barriers which can separate a managed lane facility from the general purpose lanes: permanent physical barriers, movable physical barriers, or no physical barrier. Where a permanent physical barrier is used, access to and from the managed lanes can only be accomplished at designated locations, as crossing through the barrier will not be possible. Managed lanes may have fewer access points than the general purpose lanes due to their design. Many managed lane facilities with permanent physical barriers will have full or partial shoulders on at least one side, per typical design standards. This shoulder will allow for easier access to the incident scene and for vehicles to pass around an incident.
Movable physical barriers can take several forms, including zipper barriers, plastic "candlestick" posts, or removable sections of permanent physical barriers. With this design, the most desirable access to the managed lanes is through the normal entry and exit locations; however if access from these locations is not possible, the physical barriers can be breached or moved to allow access. A plastic post barrier can easily be breached by a large vehicle by driving over the posts. Alternatively, the plastic posts can be removed from their base or other barrier types can be moved to allow access. This activity must be accomplished by ground crews at the direction of the TMC. Since the removal of the barrier requires effort and a removed barrier must be replaced, this method of accessing a managed lane is not the preferred option for accessing an incident or allowing diversion. Managed lane facilities with removable barriers may not include shoulder space or a buffer area on either side of the lanes, as these managed lane facilities are often squeezed into available space within the right-of-way. This may limit the options for responders to access an incident scene more so than a typical freeway.
Figure 20. Photo. Plastic "candlestick" posts can be moved to provide emergency access to the managed lanes.
If there is no physical barrier, accessing the managed lanes for TIM purposes is unrestricted, as vehicles can simply drive across the painted buffer. Physical access to managed lanes in these circumstances is no different than accessing an incident on a typical freeway. If there is electronic enforcement of the painted buffer, this enforcement can be suspended by the TMC during (or retroactively after) an incident.
Priced managed lane facilities involve the collection of tolls to manage demand on the facility. When an incident occurs on a priced managed lane, financial considerations will come into play. To a managed lane operator, maintaining the revenue stream from toll collections is an important objective.
When an incident occurs, a TMC may need to reduce vehicle demand on the managed lanes by eliminating the option to pay a toll for access and allowing access to HOVs only, or by raising the toll rate and having fewer vehicles paying for access. Raising the toll rate with fewer vehicles may have an adverse impact on revenue collections. In some cases, toll collection is completely suspended during an incident, such as when the managed lanes are used for general purpose lane traffic diversion.
Managed lane operators may be reluctant to take any TIM step that will reduce revenue collections. Careful consideration should be given to the available options in these circumstances, and the loss in revenue weighed against the level of service provided to drivers along the corridor. In some circumstances, it will make sense to maintain collection of tolls if capacity allows toll-paying vehicles to travel in the managed lanes without a severe degradation in service. However the managed lane operators will generally give priority to HOVs and transit vehicles in order to preserve the reliability of those modes of transportation. If there is not sufficient capacity to allow drivers to pay a toll for access to the managed lane facility, it may be logical to disallow those vehicles, even though it will cause a revenue loss, in order to preserve the level of service and reliability of the overall facility.
When the managed lane operator and the general purpose lane operator are the same, the one agency will have the ability to decide on its own when to take steps that will reduce revenue. When the managed lane operator is a different public sector agency or private sector operator, specific guidelines governing the suspension of toll collection may be necessary in order to ensure that the need for revenue collection is properly balanced with the mobility needs of drivers along the corridor.
Figure 21. Photo. Suspension of tolls in managed lanes is rare due to concerns of revenue loss, but can be implemented during large incidents, such as this region-wide snow emergency.
United States Department of Transportation - Federal Highway Administration