Traffic Signal Timing Manual
This publication is an archived publication and replaced with the Signal Timing Manual - Second Edition.
SIGNAL TIMING MAINTENANCE: OPERATIONS AND MONITORING
TABLE OF CONTENTS
- 8. SIGNAL TIMING MAINTENANCE: OPERATIONS AND MONITORING
- 8.1 Overview
- 8.2 Traffic Signal Operations
- 8.2.1 Signal Timing Maintenance Activities
- 8.2.2 Reasons for Signal Timing Maintenance
- 8.3 Day-to-Day Operations
- 8.3.1 Signal Retiming
- 8.3.2 Signal Timing Inventory
- 8.3.3 Staff Training
- 8.3.4 Responding to Citizen Calls
- 8.3.5 Incident Management and Planned Special Events
- 8.4 Staffing Needs
- 8.4.1 Background Information
- 8.4.2 Staff Positions and Roles
- 8.4.3 Staff Needs
- 8.5 References
LIST OF TABLES
- Table 8-1 Traffic Signal System Maintenance Activities
- Table 8-2 Summary of Staffing Needs
8. SIGNAL TIMING MAINTENANCE: OPERATIONS AND MONITORING
The purpose of this chapter is to summarize the various steps necessary in maintaining effective traffic signal timing plans. It will consider the various field settings that are important for response to citizen inquiries and will identify ways to address day-to-day operations of the signal system.
This chapter contains four sections. The first section presents a short overview of the many activities that correspond to the maintenance of signal timing. The second section presents a discussion of the types of activities that are completed by agencies. It will describe methods used to identify changes in the street network and use of traffic signal systems of various sizes. The third section will present a checklist of typical events (public complaints, weather, etc.) and the range of possible responses, with cross-references to the appropriate chapters in the manual. This section will also present a series of common questions and answers that can assist personnel involved in the direct line of communication with the public. The final section will highlight issues raised during the ITE traffic signal self assessment and communicate recommended staffing levels for public agency jurisdictions.
As discussed in this manual, traffic signal timing is one component of a traffic signal. As with any component of a traffic signal, a maintenance element is important to ensuring that the traffic signal will continue to operate at the level expected by the agency policies and the general public. For a traffic signal, maintenance activities range from system-oriented, such as managing a Traffic Management Center (TMC) or providing training opportunities for staff, to local-oriented activities, such as inspection and replacement of traffic signals, controllers, and detectors and reviewing traffic signal timings on a periodic basis, to other activities, such as public relations or collecting traffic data at the intersection. All of these activities are important ones to ensure acceptable operations of the signal system.
Table 8-1 highlights some of the many maintenance activities of a traffic signal system. Cells that are highlighted represent the activities specific to the maintenance of signal timing.
|System-Oriented Activities||Local Activities||Other Activities|
|Personnel Management||Maintaining Traffic Signal Operations and Inspection||Public Relations, Education, and Outreach|
|Traffic Management Center||Utilizing and Maintaining ITS Devices Operations and Inspection||Traffic Data Collection and Inventory|
|Equipment Inventory and Training||Updating Traffic Signal Timing||Utilizing Website and Information Dissemination Outlets|
|Updating Software Inventory and Training||Modifying Traffic Signal Design for Construction Projects|
|Maintenance Inventory and Management||Maintaining Detector Operations and Inspection|
|Traffic Signal System Design and Operations Training||Traffic Signal Turn-On's'|
|Updating and Maintaining Communication Design and Inventory|
|Developing and Maintaining Inter-Agency Coordination|
8.2 TRAFFIC SIGNAL OPERATIONS
This section presents a discussion of the types of activities that are completed by agencies. It will describe methods used to identify changes in the street network and use of traffic signal systems of various sizes.
8.2.1 Signal Timing Maintenance Activities
As presented above, signal operators have several maintenance activities to ensure that traffic signals are functioning properly. Some of these activities related specifically to traffic signal timing are outlined below:
- Retiming of traffic signals due to the following:
- Land use changes
- Population growth
- Change in flow profiles (volume and classification)
- Incident management
- Special Events
- Traffic signal turn-on
- Construction work zone or temporary traffic signal
- Traffic signal equipment change
- Scheduled or periodic traffic signal retiming
- High frequency or rate of crashes
- Inventory of signal timing at each traffic signal
- Maintaining a database of the traffic signals, including signal design, signal timing, and history of updates
- Staff training for use of software and equipment
- Responding to public comments
- Observing traffic conditions via a Traffic Management Center or on-site field visits
- Coordination between designers, operators, and technicians
8.2.2 Reasons for Signal Timing Maintenance
It is not possible to retime an entire group of signals every time adjustments are being considered for a single intersection. This is true, even though the intersection requiring adjustment may be part of a coordinated system. When making adjustments to a single intersection, the challenge is to do so without making things worse at neighboring intersections. In other words, the adjustments should have a positive impact on the intersection at which they are made, leading to the improved performance of the overall system.
The adjustments being made are sometimes known as retiming. Retiming may involve modifying the phasing or mode of operation to accommodate unusual congestion, adjusting the split to reflect a change in demands at the intersection, or changing an offset or green time to accommodate an incident in the field. In some cases, the offset may be modified to reflect changes in travel behavior from adjacent intersections.
The need for retiming may result from the professional judgment of the jurisdiction’s engineering staff, an incident, a new traffic signal, or the result of citizen’s calls. In all cases, the request for retiming should be taken seriously, since it reflects the observation of either trained observers or frustrated motorists, field incidents, or construction.
Signal Retiming: The need for review and adjustment of signal timing at a single intersection could be the result of a variety of different factors including:
- Changes in traffic demand since the intersection was last timed. This could include changes in side street demand, turning movement volume or spill back, main street demand, or vehicle mix (for example a higher percentage of trucks). Changes in vehicle demand could also be reflected in general increases in demand that cause the need for longer periods with peak period timing, and the modification of night time flash operations.
- Changes in intersection operations (for example addition of an approach lane or the moving a bus stop from near side to far side) that influence the need for timing.
- Changes in pedestrian traffic due to land use changes (for example the opening of a residence for the elderly which required longer pedestrian clearance times) or the need for handicapped features.
- Changes to agency policies or national standards, such as the Manual on Uniform Traffic Control Devices.
- Temporary changes in roadway operations due to construction
- Observations of previously unnoticed conditions by an alert motorist or staff member or through use of a Traffic Management Center
- Agreements with other jurisdictions to coordinate with their signal systems, or to provide coordinated response to incidents on parallel facilities
From the length of this list, it is clear that, in most systems, signal retiming will be required frequently at various intersections throughout the system. It is important to recognize that there is a point at which so many localized adjustments have been made, that it becomes essential to initiate system-wide signal retiming as described in Chapter 7.
Traffic Signal Inventory: One of the items related to signal timing maintenance is the importance of maintaining an inventory of the traffic signals. The database should include information related to the traffic signal, such as location, signal layout, signal timing, coordinated or uncoordinated signal operation, communication, operating agency, history of updates, etc. A database provides the agency with a knowledge base of what changes have occurred and what might need to be updated in the near and long term at the signalized intersection.
Staff Training: The equipment and software utilized by many agencies on its traffic signal system is only as good as the availability of skilled and trained staff. Therefore, a valuable component of the traffic signal maintenance is ensuring that the staff managing and maintaining the traffic signals has been trained to operate the system. Critical training elements highlighted in the FHWA Guidelines for Transportation Management Systems: Maintenance Concept and Plans (1) included:
- Training by Vendors: Procurement contracts should include a requirement for on-site training of Agency staff in maintenance and operations of the equipment, preferably conducted by the vendor.
- Training by Contractors: Procurement contracts should also include a requirement for on-site training of Agency staff in the maintenance and operation of the assembled systems, including software, hardware, and devices.
- Training Library: The operating Agency should maintain a library of system documentation and, if available, a videotape or DVD library of training.
- Staff Retention: This can be difficult in a high-tech environment, but there are ways to improve retention, such as providing for additional training, allowing travel to technical conferences, and workshops and other non-salary related perquisites for Agency staff. 8-3
As noted in these guidelines, the key to success in this ever-changing environment is flexibility and a good understanding of priorities for both operational and maintenance concepts, requirements, and training.
Incident Management: Traffic patterns for special events, roadway construction, inclement weather, crashes, etc. are different from those that exist during normal traffic conditions. It is important for agencies to develop and utilize an incident management plan for its signal system. Goals of these plans related to signal timing might include sustaining or increasing corridor capacity during an event through longer green times at a traffic signal, enhancing public safety though modified time settings could reduce delays for emergency responders traveling to an incident on the roadway, and guiding motorists to a certain destination. Chapter 9 provides further discussion on this topic.
Public Comments: Calls from the public are one of the most common reasons for reviewing intersection operations. It is important that each agency has a process in place to field public phone calls, emails, etc. and addresses their responses in a timely, professional manner. More discussion on this item is presented in the next section.
8.3 DAY-TO-DAY OPERATIONS
This section will present a checklist of typical events (public complaints, weather, etc.) and the range of possible responses, with cross-references to the appropriate chapters in the manual. This section will also present a series of common questions and answers that can assist personnel involved in the direct line of communication with the public.
8.3.1 Signal Retiming
Since the need for retiming could have been identified by a number of different sources for a variety of different reasons, it is difficult to define a single procedure that might be applicable to all possible sets of conditions. However, in most cases, the following procedure should be followed, with all actions recorded:
- Schedule the field visit for the time-of-day and type-of-day (weekend, weekday, etc.) for which the problem was identified.
- Assemble the timing and configuration information for the intersection being visited. If the intersection is included in a system, timing information should include master clock, offsets, and time-of-day schedules for plan changes. Information should also include controller settings. If available, traffic count data should also be included.
- If the intersection is included in a system, coordinate with system operators to ensure that operations personnel will be available by radio contact to support the field activities.
- When arriving at the intersection, observe the physical condition of the street hardware including poles, mast arms or span wires, signal head positioning, signal lamp operation, pedestrian indication operation, and cabinet condition.
- Open the cabinet and perform a physical inspection of the cabinet interior including cabling, physical condition and operation of cabinet components, air filter and fan.
- Check operability of all cabinet components either through observation or suitable maintenance diagnostics.
- Review controller timing by comparing settings with timing documentation
- Qualitatively compare traffic conditions at the intersection with the traffic count data. Determine whether major changes in demand have occurred since the traffic counts were taken to support the development of the timing plans currently in use. If major changes have occurred, determine whether they are temporary (due to nearby construction) or permanent. If they are temporary, it is still desirable to fine-tune the intersection timing. However the log completed as the final step should include a notation that a second set of fine-tuning may be required when the construction has been completed.
- If the deficient intersection operation occurs during heavy traffic conditions, the next step would be to determine whether the adjustments are intended for congested or under-saturated conditions. The procedures should be followed from the appropriate section below.
- If the deficient intersection operation occurs during light traffic conditions, the procedures of the section for “Other Types of Traffic Conditions” should be used.
- If the deficient intersection operation is related to the use of an incorrect timing plan, (assuming a correct plan is available), the procedures associated with the selection and scheduling of plans under “Other Types of Traffic Conditions” should be used.
- In all cases, after timing and/or scheduling changes have been made, the impact of the changes should be evaluated through observation of the intersection operation.
- The final step of this process is to log the actions taken. This is essential for response to the individual initiating the fine-tuning, as well as records that must be maintained by the agency for a variety of engineering, operational and legal reasons.
Refer to Chapters 2, 5, 6, and 7 for more details on retiming at an intersection or a series of intersections.
Retiming for Under-Saturated Conditions: It is likely that the most frequent requests for intersection fine-tuning will occur during normal flow conditions. These are the conditions that impact a large number of motorists, all of which expect high signal timing quality. Motorists will be annoyed at instances of wasted green time during which they have to wait at a red signal indication when there are no vehicles on other phases. Motorists will also become annoyed at locations where they have to stop at successive signals due to poor offsets. In some cases their complaints are unjustified, since they are not aware of other constraints on signal timing, such as pedestrian clearance times and the need to make compromises in progression in order to accommodate flow in the reverse direction. However, in other cases, their complaints are justified, and should be addressed whenever possible by the agency’s engineering and technician staff.
When retiming an intersection for free-flow (under-saturated) conditions, the following steps are recommended:
- Perform a qualitative evaluation of the intersection performance to determine whether any obvious improvements are possible.
- Adjust the split to reflect demand on competing approaches.
- Adjust the offset to reflect platoon arrival times.
- Review the cycle length for possible improvements.
Retiming for Congested Conditions: It is important to recognize different traffic signal timing strategies for networks that experience congested traffic conditions or more normal traffic flow conditions. Strategies begin to change from mobility and progression to queue management. Congestion can be recognized by the presence of queues at signalized intersections that are not completely discharged during the green period. This is known as cycle failure. If the deficient intersection operation occurs and consider measures such as:
- during heavy traffic conditions, the next step would be to determine whether the adjustments are intended for congested or under-saturated conditions. The procedures should be followed from the appropriate section below.
- during light traffic conditions, the procedures of the section for “Other Types of Traffic Conditions” should be used.
- related to the use of an incorrect timing plan, (assuming a correct plan is available), the procedures associated with the selection and scheduling of plans under “Other Types of Traffic Conditions” should be used.
- In all cases, after timing and/or scheduling changes have been made, the impact of the changes should be evaluated through observation of the intersection operation.
When re-timing a congested intersection, the split and cycle length should be reviewed and adjusted as necessary. When an intersection experiences congested conditions, there may not be a need to consider offset adjustments, except for the qualitative evaluation of intersection operations, since continued traffic flow between intersections may not possible. The following process is should be used:
- Perform a qualitative evaluation of intersection operation.
- Adjust the downstream intersection signal offset to permit earlier discharge of left turning vehicles, to minimize the possibility that these vehicles might block through movements.
- Change the signal phasing as needed to avoid spillback from left turn bays, or to make more effective use of concurrent phases.
- Modify pedestrian phasing to minimize pedestrian/vehicle conflicts
- Review and adjust the split as required.
- Review and adjust the cycle length if necessary.
- If these approaches prove ineffective, consider using some of the “other measures” described below.
- Driveways near the intersection which potentially block the through flows, and which may include weaving movements might be eliminated
- Parking can be banned
- Double parking regulations might be rigorously enforced
- Bus stops might be moved from near-side to far side. This is particularly useful in the presence of heavy right turning traffic
- The number of phases might be reduced. For example, some jurisdictions ban left turns at critical intersections to increase available capacity for through movements
- Phasing might be changed to avoid the problem of left turning vehicle blocking through movements. This might be accomplished by substituting leading left turn phases for lagging phases, or in some cases both leading and lagging phases might be provided.
- Increasing the length of turning bays can reduce the problem of left turn blockages
- Other geometric improvements are possible including addition of lanes and overpasses
If all else fails, metering traffic entering the control area should be considered. Metering is performed by reducing the number of vehicles traveling on the congested arterial, through significant reduction of green times available to entering side street traffic. The use of this technique avoids spillback into upstream intersections, intersection blockage and overflow of turning bays.
8.3.2 Signal Timing Inventory
A short discussion was provided in Chapter 7 regarding this topic. Area-wide or corridor-focused signal retiming projects include a lot of information, such as traffic data, intersection geometry, signal phasing, signal timing, controller type, and posted speeds. Thus, it is important that this information be managed in a database to assist with a record as well as for future retiming updates. Documentation of the goals and outcome of the retiming process is also important. The following is a list of items that are typically collected in a signal retiming project:
- Types of signal control at each intersection
- Intersection signal phasing
- Signal timing plans
- Measures of effectiveness (both estimated and evaluated)
- Traffic volumes and speeds for the network
- Geometric description of the network
- Input data files for simulation and traffic signal timing software
- Software files that include network and traffic signal timing for the system
The signal timing process is greatly simplified, and its cost reduced, when this data is stored in a database that can be accessed each time area-wide signal timing is developed. However, as with any database, its value will be reduced if it is not kept up to date. It is essential that the database be updated each time controller operation is modified, including all changes in phasing, type of control, timing, or intersection geometrics. In this way the value of the database can be preserved for access during the area-wide signal timing process.
Furthermore, the above information relates to maintaining a database from a signal retiming project. Additional information can be added based on the following items to create a comprehensive database of the traffic signal system.
- Signal equipment failures and changes
- Public comments
- History of signal timing changes
- Crash data
- Other incidents reported near the intersection
- Changes in land use
By recording the above information in a comprehensive database, the agency will improve its effectiveness on managing a traffic signal system.
8.3.3 Staff Training
A valuable component of the traffic signal maintenance is ensuring that the staff managing and maintaining the traffic signals has been trained to operate the system. Depending on the size of the traffic signal system and number of staff, a regional or local training program may be established to provide training opportunities for staff.
Training activities could be as simple as peer exchanges within or between agencies or offering a series of technical sessions. These technical sessions could consist of bringing in outside experts to discuss important signal timing, software, and maintenance topics and offered on a regular monthly basis. Other topics might be directed towards TMCs and specific signal timing projects. Other training opportunities might be provided through attendance at conferences, education seminars, or universities.
Lastly, a public relation component that incorporates training might be offering short work sessions or seminars open to the public or other agency officials that would provide insight into signal timing and traffic operations.
8.3.4 Responding to Citizen Calls
Citizen’s calls and emails are one of the most common reasons for reviewing intersection operations. The public may obtain the contact information for emailing or making a phone via a newspaper, website, or television/radio show. Some agencies include a sticker with the logo, phone number, and catch phrase on the outside of the traffic signal controller cabinet to assist the public with obtaining the correct contact information. The call could have been initiated for a number of reasons including:
- Lack of understanding of intersection and controller operations
- A signal that was in transition between two different timing plans
- An equipment failure
- A legitimate observation regarding a shortcoming in the existing timing
- An incident near or at the intersection that impacts the traffic operations
Motorists often have a surprisingly sophisticated understanding of intersection operations resulting from their familiarity with a given roadway. For this reason, as well as for possible reasons of safety, their calls should be taken very seriously. A well-managed signal operations organization will employ the following procedures in response to citizen’s calls which could arrive by telephone, email or letter:
- Identify the name and contact information of the caller.
- Identify the location that is the subject of the contact.
- Define the time-of-day for which the problem is being described.
- Ask for a description of the problem in terms of traffic conditions and traffic signal operations.
- Assure the caller that the problem will be investigated within a predefined number of days that has been established by agency policy.
- Enter all information provided along with the time and date of the contact into a database.
Investigation of the problem should be scheduled as part of the agency’s maintenance operations. If adjustments to the signal operation are required, the procedures described later in this chapter should be followed. In all cases, the results of the investigation should be recorded in a database and described in a response to the caller using the same media (telephone, email or mail) that was used to make the original contact. If no change was made, the reason for maintaining the status quo should also be explained.
Some jurisdictions have websites that permit citizens to report problems and concerns using an automated questionnaire that guides them through the process of providing the information described above.
A website may be used to record input and provide an estimate of response time, and enters the information provided into a database. This is a particularly effective technique in regions where multiple jurisdictions are involved with signal operations and maintenance. In this case, callers are uncertain of the agency to be contacted. A website could be established for the region, which directs problems and complaints to the appropriate agency without requiring citizens to determine the responsible agency. Examples of such websites include the Cities of Scottsdale, Arizona, Durham, North Carolina, and Tampa Bay, Florida.
While some agencies utilize sophisticated call-processing software which handles the database functions described here, this capability is not necessarily required. Smaller agencies can use simple spreadsheets to keep track of the disposition of citizen’s calls. In either case, it is critical to ensure that all calls are investigated, and that a response is provided to the caller in a timely manner. Ideally, a response should be received by the caller within one week of the date that the initial contact has been made. Responsive service is the key to good customer relations.
8.3.5 Incident Management and Planned Special Events
Signal timing can play a role in managing and even mitigating certain types of non-recurring congestion. In particular, the high volumes of traffic generated by planned special events, the reduction of corridor capacity from roadway incidents, or the increased travel demand triggered by region wide evacuations can necessitate signal timing changes. A primary goal of readjusting signal timing in these circumstances would be to give priority to specified movements and to minimize the overall delay experienced by users from the non-recurring congestion. One way to achieve this objective would be to sustain and/or increase the throughput of traffic at certain intersections by increasing the green time for those movements. Traffic signals with modified timings settings perform this function by essentially “flushing” the preferred movement.
The techniques to modify signal timing during planned special events, roadway incidents, or evacuations involve processes not just in traffic operations and planning, but also require some management and coordination at the policy and institutional levels. On the operations/planning side, an initial step would be to determine the specific route and intersections where traffic signals would be retimed. This route could be a particular arterial that is parallel to a certain freeway. In the event of an incident on the freeway, traffic could then be diverted from the freeway to this arterial, which could provide additional capacity with the modified timing settings in place at its various traffic signals.
Adjustments to the cycle length and green time for a particular movement are typical components of an incident management plan. Additionally, utilization of a traffic management center would be required for monitoring of the intersections during these changes to ensure that the operations are working, as well as, if necessary, permits the use of manual control by an operator.
These operational procedures may not be effective or possible without a sufficient level of coordination among the jurisdictions impacted by the traffic from planned special events or emergency situations. This inter-jurisdictional coordination is needed among such institutions as law enforcement, public safety organizations, and various transportation/transit agencies to share resources, seamlessly exchange the required information, and to implement the required traffic control/signal timing plans. With such effort to coordinate between many stakeholders, it would be necessary to develop various response and contingency plans ahead of time and updated on a regular basis. Overall, from achieving both the non-operational and operational sets of goals, adjusting signal timing can offer significant benefits to eventually reduce delays for motorists during special events, roadway incidents, or evacuations. More discussion is provided on this topic in Chapter 9.
8.4 STAFFING NEEDS
This section will highlight issues raised during the ITE traffic signal self assessment and communicate recommended staffing levels for public agency jurisdictions.
8.4.1 Background Information
This section provides some background information regarding staffing needs that are included in several literature documents.
ITE Traffic Engineering Handbook and Traffic Control System Operations: Installation, Management and Maintenance Manual: These documents suggest labor requirements of 20 to 25 hours per intersection for traffic signal retiming and estimates as a rule of thumb that one traffic engineer is needed to properly operate and maintain every 75 to 100 signals and one technician to operate and maintain every 40 to 50 signals. As a rule of thumb these estimates are adequate; however the current transportation environment requires much more detailed estimates.
Traffic Signal Operations and Maintenance Staffing and Resource Requirements Guidelines: These guidelines are part of a new project put forth by the FHWA. The objective of this effort is to develop a guideline to assist agencies in developing a staffing and resource plan to effectively operate and maintain traffic signal systems. The background information provided as part of this project suggests that the current guidance available to agencies is very general and not achievable for most jurisdictions. The lack of a credible guideline for traffic signal operations and maintenance staffing and resource needs is one of the factors that has resulted in the inefficient operation and maintenance of traffic signals on a national scale.
8.4.2 Staff Positions and Roles
An agency may need a variety of staff positions and roles to adequately operate and maintain its traffic signal system. Depending on the size of the signal system, some of these positions may be combined due to a combination of small signal system and limited funding available. The roles of each position described below are based on information from agencies in addition to relevant ITE and FHWA literature. Some of the positions and respective roles are.
Traffic Signal Engineer - This staff person is responsibly for the day-to-day operations of the signal system. Tasks include the following: Responding to public comments, approving new signal turn-on’s, assisting in the TMC, evaluating signal timing on existing arterials, managing signal operations staff and coordinating with the signal design and maintenance supervisors.
Traffic Signal Technician/Analyst - Staff assist the Traffic Signal Engineer with their day-to-day operations. Focus areas include signal timing, new signals, and the TMC.
ITS Engineer - This staff person is responsibly for the implementation of ITS projects. Tasks include the following: Responding to public comments, evaluating new products, assisting in the TMC, managing ITS contractors and vendors and coordinating with the signal design and maintenance supervisors.
Traffic Signal Maintenance Technician – Staff are generally responsible for troubleshooting and maintenance of the physical traffic signal equipment.
Electronic Specialist – Staff are responsible for the complex electronic equipment at the heart of the signal system. Some tasks include:
- Closed circuit television system repair, field and central system
- Fiber optic cable system testing, repair, termination
- Telecommunications systems maintenance and repair
- Traffic management center systems maintenance and repair
- Traffic signal controller electronics testing repair and inventory
- Other ITS devices repair
TMC Operators – Staff are responsible for observing the traffic conditions, responding to incidents that occur in the field, and providing support to homeland security efforts. Their role is critical to the rapid response and resolution of the situation.
Public Relations Coordinator – Staff are responsible for field phone calls from the public, coordinating with the Traffic Signal Engineer and Technician on responses, and marketing the TMC, incident management plan, and traffic signal operations to the public. Depending on the size of the agency, this position could be a full-time position or these tasks might be passed on to the Traffic Signal Engineer and Technician.
8.4.3 Staff Needs
The ITE “Traffic Control System Operations” manual suggests that a traffic signal system should have one traffic engineer per 75 to 100 traffic signals and one signal technician per 40-50 traffic signals or other field devices. An NCHRP report (Synthesis 245) also suggests 38 to 43 signals per technician. The manual also provides staffing guidelines for a continuously operated TMC which includes one center manager, two supervisors, and five system operators.
Overall, the current literature provides limited guidance on staffing for complex traffic signal systems that include a multitude of components ranging from traffic signals to video detection to ITS devices to incident management plans and a TMC. With the above limitations in mind, Table 8-2 provides general guidelines on staffing needs for a traffic signal system as it relates to signal retiming.
|Position||1 to 50 Traffic Signals||51 to 100 Traffic Signals||101 to 200 Traffic Signals||201 to 500 Traffic Signals||501 to 1000 Traffic Signals|
|Traffic Signal Engineer||0 to 1||1||1 to 2||2 to 5||5 to 10|
|Traffic Signal Analyst/Technician||0 to 1||0 to 1||1||1 to 3||3 to 5|
|ITS Engineer||-||-||0 to 1||1||1 to 3|
|Traffic Signal Maintenance Technician||1 to 2||2 to 4||4 to 7||7 to 17||17 to 33|
|Electronic Specialists||1||1||1 to 2||2 to 4||4 to 9|
|TMC Operators||-||-||2||2 to 4||4 to 9|
|Public Relations Coordinator||0 to 1||0 to 1||1||1||2|
Additional research in this area is necessary because all agencies vary in terms of the infrastructure, their staff’s skill levels, and the environment the equipment operates. For example, a signal technician that has ten years of experience with a particular traffic controller is likely able to troubleshoot a problem in less time then a technician with less experience. In many cases, the difference in staff time needed is significantly higher, while the cost to the agency may be insignificant. This particularly effects agencies with high levels of staff turnover and is a notable problem for many agencies throughout the country.
Another example of this is use of older infrastructure may be less user friendly or it may fail or malfunction more often because of the environmental conditions which the traffic signal equipment operate. As with staff experience there is not specific research on the performance of traffic signal equipment over time and new equipment can result in other problems for agencies, but by utilizing a systems engineering approach during the selection and procurement of new traffic signal equipment, an agency may reduce the maintenance costs (staffing and consultant time) needed for the signal system.
Several agencies maintain signal systems that operate in the DOS environment (an operating system that was before Windows). In most cases, these systems are not supported by Information Technologies (IT) staff and access to data leads to inefficient operations or requires special maintenance by agency personnel.
Proximity to traffic signals is an important consideration, especially in staffing needs for technicians that are tasked with responding to field complaints or maintenance problems. A city with a large downtown may have 100 signals within a square mile (Manhattan, Portland, OR for example) that are fixed time without detection as opposed to a rural district with 100 signals over a 100 square mile area. Obviously, in these cases, the staffing needs are likely different and may require different skill sets. This may be exacerbated by an agency that utilizes different controller types supplied by various vendors. Many agencies are transitioning from an older standard, thus requiring careful scheduling for staff training and equipment management.
The Federal Highway Administration has recently conducted several Regional Traffic Operations Program Assessments to determine the sufficiency of staff within a region to perform basic signal operations activities for individual jurisdictions. In many cases, these reviews have shown that there are opportunities for improved operations through the use of regional approaches to problem solving, equipment procurement and testing, staff training, and performance measurement.
Additional research in this area is needed to further identify specific needs by agency, as each jurisdiction has special circumstances that may either overstate or understate the need described in Table 8-2. Overall, findings from the National Traffic Signal Report Card indicate that traffic signal operations could be improved with increased investment.
- Vick, C. and R. Sumner, “Guidelines for Transportation Management Systems Maintenance Concept and Plans”, Federal Highway Administration, 2002.