Roadway Safety Principles and Practices
in Temporary Traffic Control Zones
John C. Glennon, D. Engr., P.E.
Standard traffic control devices as presented in Part 6 the Manual on Uniform Traffic Control Devices (MUTCD) are particularly important during roadway construction. Because of changing and unexpected traffic conditions, drivers are more dependent on traffic control devices to guide them safely through what would otherwise be a hazardous area.
The effectiveness of traffic control devices in temporary traffic control zones depends on their ability to satisfy the driver's need for information. Both the message content and the placement of traffic control devices is important. The positive guidance principles of providing clear and simple standard messages that command driver's attention at a point where they have adequate time to properly respond are the basis of any good traffic control plan.
Past experience indicates that the most serious failures to meet driver needs result from:
2. Misleading information.
3. Messages with incorrect distances.
4. Non-standard traffic control devices.
5. Incorrect signs.
6. Transitions that are too short or are curved too sharply.
Basic Safety Principles
Section 6B.01 of the MUTCD is a good statement of basic safety principles as paraphrased below:
2. Normalize Design and Operations - Apply the basic safety principals governing normal roadways and roadsides to the design and operation of temporary traffic control zones.
3. Minimize Traffic Interruptions - Inhibit traffic movement as little as practical. Minimize the time that work activities occupy the roadway. Recognize that drivers will not reduce their speed unless they perceive a real need to do so. Employ flaggers only when all other traffic control methods are inadequate.
4. Design for Positive Guidance - Avoid frequent or abrupt changes in geometrics that will surprise drivers. Guide drivers with traffic control devices that give a clear and positive message. Remove traffic control devices that are inconsistent with the intended path.
5. Monitor Operations - Observe both heavy and light traffic, during day and night, and under varying weather conditions to make sure all traffic controls are operating effectively. Analyze traffic collisions that might indicate a need for changes in traffic control.
6. Train Personnel - Only assign people who are trained in proper traffic control practices to the responsibility of selecting, placing, and maintaining temporary traffic control devices. Also train every person whose actions affect safety, from upper-level managers to fieldworkers, in those principles consistent with the job decisions they are required to make.
7. Maintain Clear Roadside Recovery Areas - Maintain a roadside recovery area free of equipment and materials.
Traffic Control Plan
For most major construction projects, the contractor is required to follow the contract's Traffic Control Plan (TCP), the Manual on Uniform Traffic Control Devices (MUTCD), and the highway agency's standard specifications. If the TCP is wisely conceived, explicit in content, and anticipates all conceivable operational and/or construction activities, safety will be well served. A dilemma arises, however, when these desirable aspects are only partially achieved, and the safety of the motoring public is left to contractor employees and highway agency resident engineers, neither of which usually has a grasp of basic safety principles.
A formal TCP is a required document for all Federal-Aid roadway construction projects. The TCP is a plan for guiding traffic through the construction or maintenance area. It should provide for the safety of pedestrians, motorists, and workers.
The TCP describes the temporary traffic control zone layout, the traffic operational elements, and the traffic control devices needed to safely move traffic through the construction zone during each phase of construction. The details of the TCP should be consistent with the complexity of the project. For example, TCP's can range from a very comprehensive multi-phased plan for a high-traffic urban freeway to a single-phased plan for a two-lane rural road that simply refers to either a typical drawing in the MUTCD, a roadway agency standard plan sheet, or a simple drawing in the contract.
Traffic Control Devices
Channelizing Devices - These devices include but are not limited to cones, tubular markers, vertical panels, drums, barricades, and barriers. The major function of channelizing devices is to provide a clearly visible path to guide drivers safely past the hazards of the temporary traffic control zone.
Channelizing devices should provide smooth and gradual traffic movement either from one lane to another, onto a detour or diversion, to laterally shift the travel lanes, or to reduce the width of the traveled way. They are also used to separate traffic from either the work space, pavement edge drop offs, or opposing lanes of traffic.
Channelizing devices are integral elements of the total system of traffic control devices used in temporary traffic control zones. These elements shall be preceded by a subsystem of warning devices that are adequate in size, number, and placement for the type of roadway.
Pavement Markings - The MUTCD mandates that adequate pavement markings complying with its Part 3 be maintained in temporary traffic control zones. It also requires that markings that are no longer applicable and might confuse drivers be obliterated as soon as possible. Obliterated markings shall be unidentifiable as pavement markings under day or night, and wet or dry conditions.
2. Positive Guidance in Traffic Control, Gerson J. Alexander and Harold Lunenfeld,
Federal Highway Administration, April 1975.
3. Roadway Safely and Tort Liability, John C. Glennon, Lawyers and Judges Publishing Co., 2004.
About the Author
Dr. John C. Glennon is a traffic engineer with over 45 years experience. He has over 120 publications. He is the author of the book "Roadway Safety and Tort Liability" and is frequently called to testify both about roadway defects and as a crash reconstructionist.
RESUME OF JOHN C. GLENNON