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21st Century Operations Using 21st Century Technologies

Use of Freeway Shoulders for Travel — Guide for Planning, Evaluating, and Designing Part-Time Shoulder Use as a Traffic Management Strategy

Chapter 9. Day-to-Day Operation

Part-time shoulder use has unique maintenance, incident management, and law enforcement needs. Early applications of part-time shoulder use in the U.S. were done with little or no intelligent transportation systems (ITS) support. As ITS technology has advanced, it has been increasingly integrated into part-time shoulder use operations.


Maintenance of lanes designated for part-time shoulder use is more similar to maintenance of general purpose lanes than maintenance of a shoulder. Over time, agencies with part-time shoulder use have found it is most efficient to maintain the shoulder at the same level as general purpose lanes. There is no need to clean the shoulder with street sweepers, as the presence of traffic on the shoulder moves debris off of it similar to a general purpose lane. Conducting maintenance on part-time shoulder use segments that requires maintenance vehicles to stop on the shoulder will need to be conducted at times the shoulder is closed to traffic. On high volume freeways where part-time shoulder use is most commonly used, there may already be restrictions on maintenance during peak period when the shoulder lane would be open.

After snowfall, part-time shoulder use is typically plowed after all general purpose lanes on the freeway have been plowed. This creates the potential for the shoulder to be closed during a period when it is scheduled to be open, although this usually has little effect on traffic operations due to reduced traffic volume during snow. Minnesota has found it beneficial to open the I-35W dynamic part-time shoulder use segment throughout the duration of a snowstorm because vehicles driving in the shoulder help to distribute salt that has been spread there.

Reduced lateral offsets to obstructions may not provide sufficient space to push and store snow beside the shoulder. Minnesota and Massachusetts have not experienced issues with this, but Virginia has on I-66. On average, less often than once a year a storm produces enough snow that it cannot be fully plowed off of the shoulder in several constrained areas. Loaders and dump trucks are used to remove the snow from these areas in nighttime hours. The time and cost associated with this are high enough that it would not be feasible if Virginia received more snow and it was necessary to remove snow several times per year.

Incident Management

Part-time shoulder use is typically implemented on some of the highest volume and most congested freeways in a region. These roadways typically have incident management plans and infrastructure in place that can be adapted for part-time shoulder use. Strategies for enhanced incident management on part-time shoulder use facilities include the following:

  • Emergency turnouts, discussed in the Geometric Design chapter, constructed approximately every half-mile unless other turnouts such as ramps are present.
  • Service patrols, especially for longer part-time shoulder use spanning multiple interchanges.
  • CCTV coverage of shoulder lanes and turnouts.
  • Devices to detect slow or stopped traffic on shoulder lanes or in turnouts.
  • Dynamic lane control signs:
    • A shoulder can be closed for safety reasons if a disabled vehicle stopped on the shoulder
    • A shoulder can be closed to traffic so emergency responders can drive on it to rapidly reach a crash scene anywhere on the facility.

Most static and dynamic part-time shoulder use facilities employ some of these strategies. Bus- on-shoulder (BOS) facilities, including those in Minnesota, typically do not have additional incident management specifically associated with BOS.

Law Enforcement

The success of part-time shoulder use depends on the extent to which drivers comply with posted hours of operation or lane-use controls, as well as any vehicle restrictions. In Europe, agencies often use automated enforcement for temporary lanes. Such automated enforcement in the U.S. is uncommon outside of school and work zones, and there are legal restrictions on automated enforcement in many states. Accordingly, an increased traditional law enforcement presence will likely be needed on facilities with part-time shoulder use. Enforcement of BOS lanes is focused on use of the shoulder by non-buses, and enforcement of static and dynamic part-time shoulder use is more focused on use of the shoulder outside of hours of operation.

With the increased likelihood of vehicles on the shoulder, including violators when the shoulder lane is closed, police conducting routine enforcement may want to target areas with downstream pull over opportunities such as exit ramps, emergency turnouts large enough for two vehicles, and so forth. Ultimately, law enforcement personnel should be engaged in the planning and design of shoulder lanes and specific design needs for local enforcement entities should be incorporated into the facility.

Even without automated enforcement, installation of some of the hardware associated with it, such as presence and speed detectors, may be helpful to track compliance on a system level and help target areas for enforcement by police. On dynamic part-time shoulder use facilities, lane control technology may include mechanisms for providing real-time information to police officers in the field about the status of the shoulder, when it was opened/closed, and the current lane assignment displays (for patrol vehicles in locations where displays are not visible). This technology can also be used on a static shoulder lane facility with a high level of ITS infrastructure.

On BOS facilities, shoulders can still be used by police to pull over vehicles, and bus drivers are trained to reenter general purpose lanes when a shoulder is obstructed. Police and bus operators in Minnesota have determined buses should reenter travel lanes approximately 500 feet upstream of a police car stopped on the shoulder, and bus drivers can estimate this distance in Minnesota based on the standard spacing of light poles along freeways.(44)

Opening and Closing Part-time Shoulder Use Facilities

The opening and closing of part-time shoulder use facilities in the U.S. open to more than buses is a largely manual process. A shoulder should be inspected in entirety before each opening by “sweeping” (driving) the length of the facility or viewing CCTV if there is full camera coverage of the facility. Any debris or disabled vehicles should be cleared prior to the scheduled opening time of the shoulder. If dynamic lane use control signs are present, then they can be used to keep the lane closed past the scheduled opening time if additional time is needed to clear the shoulder. Additionally, if an incident occurs while the shoulder lane is open and the shoulder becomes blocked, then the shoulder should be closed as soon as possible if dynamic lane assignment signs are present. Interagency agreements should be prepared prior to the implementation of part-time shoulder use to determine which agencies have the authority to instruct the TMC to close the shoulder.

BOS lanes do not need to be inspected before opening, and most are not. If buses encounter obstructions on the shoulder, then they can merge into traffic to avoid them, and dispatchers can alert buses on part-time shoulder use routes of known obstructions. Additionally, many BOS lanes are used on an as-needed basis and there are no fixed hours of operation.

The extensive ITS requirements and variable hours of operation of dynamic part-time shoulder use facilities make them well-suited for more automated opening and closing processes. Some of these processes may also be used for static part-time shoulder use if sufficient ITS infrastructure is in place. Agencies should be cautious with introducing too much variability into the operating hours of dynamic part-time shoulder use. For example, if a shoulder needs to be opened in the morning peak period for congestion reduction purposes nearly every weekday, it will be more predictable to drivers if it is opened at the same time every weekday (such as 7 a.m.) rather than different times (such as 6:50, 7:10, 7:15, etc.) based on minor variations in traffic from day to day. In this case, the benefits of dynamic over static part-time shoulder use would still be realized by the ability to extend the operating hours if high traffic volume was still present at the end of the typical a.m. peak period or occasionally open the shoulder at other times such as weekends.

The long-term costs of an increased number of operators to continuously monitor dynamic part- time shoulder use and other ATM features, if they are present, may be greater than having software to assist with part-time shoulder use (and general ATM) operation. In Europe, some facilities with ATM are controlled by “an expert system that deploys the strategy based on prevailing roadway conditions without requiring operator intervention.”(46) Opening or closing a shoulder as a fully automated process is not recommended for the U.S. at this time because ATM is less common than in Europe. However, expert systems can be used to provide recommendations to human TMC operators, who then ultimately decide whether to open or close a shoulder based on the recommendation. Although expert systems can electronically, rather than manually, sweep a facility, it is still necessary to have incident response vehicles on standby in the event that debris or disabled vehicles are identified and need to be cleared.

An expert system—also known as a Decision Support System (DSS)—continuously monitors data and other performance parameters collected from the field devices (e.g., speeds and volumes; status of shoulder (blocked / clear); confirmed incidents, location, severity, number of lanes blocked, anticipated duration; scheduled events; weather and pavement conditions; equipment status; and time of day and day of week). Inputs from field devices will need to be supplemented with inputs from TMC operators, such as schedules of special events and police reports of incidents. Through a series of IF, AND, OR, and THEN logical statements, this DSS implements or recommends the most appropriate response plan.

The logical statements typically involve comparisons of real-time parameters with various threshold parameters, such as comparisons of speeds and volumes with the time of day and known special events. Examples of outcomes from an automated system include:

  • Providing advisory messages to TMC operators
  • Switching sign displays
  • Switching text messages and contents on CMS
  • Sending a notification to others (e.g., State Police)
  • Automatically resetting signs to normal once an incident clears
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