 Traffic control devices include signs, signals, lighting units, pavement marking, delineators, channelizing devices, and hand signals or flags, which are used to warn, guide, or regulate traffic. This park discusses elements of design, proper application, and placement for these devices. These are classified as regulatory, warning, and guide signs. Regulatory signs impose legal restrictions and may be used only with permission from the authority having jurisdiction over the roadway. There are several types of regulatory signs. Some are typically rectangular, with the long dimension vertical. The standard color scheme is black lettering on a white background. A red circle with a diagonal slash may be used with a black diagram to indicate a prohibitive maneuver. Red is used as the predominant color for stop, yield, do not enter, and wrong way signs. The unique shapes and color schemes increase the attention-getting value for these important signs. Warning signs are used when conditions are potentially hazardous to traffic. They should be used when such conditions are real, particularly when the danger is not obvious or cannot be seen by the motorist. Most warning signs are diamond-shaped with one diagonal vertical. One exception is the advanced railroad crossing warning sign, which is round. Permanent warning signs have a black legend on a yellow background, while construction and maintenance warning signs are a special series with the black legend on an orange background. The orange color indicates a temporary condition and the potential hazard of the work site. Warning signs should be placed well ahead of the site to give the motorist enough time to understand and then respond to the information. Guide signs show destinations, directions, services, points of interest, and other geographical or cultural information. Informational signs are required at work zones for standard route markings when temporary route changes are necessary. Directional signs and street name signs are used with detour routing and may have a black legend on an orange background. Special information signs relating to the work being done also have a black message on an orange background. Some examples are roadwork next five miles, end roadwork, detour, pilot car follow me. Standard signs and messages as shown in the manual on uniform traffic control devices should always be used. Drivers are familiar with those signs and they know how to react, but non-standard sign messages could be confusing. All signs should be made in a professional sign shop or purchased from a reputable business. Homemade signs are immediately suspect and do not command driver respect. Now when choosing signs, the following should be considered. Choose signs that are appropriate, that accurately describe the work situation. Use your common sense and the manual on uniform traffic control devices in selecting signs. Use specific warning signs to warn of specific hazards, not general signs that simply say men working. The message on signs should tell what action the driver needs to take. Use larger signs when greater visibility is needed especially with high speed or volume. At the beginning of the work area, start with an advanced roadwork ahead sign. Then use signs with more specific messages, with the most specific sign stating what action should be taken by the driver closest to the work area. Drivers sometimes forget what they're told, so the last sign in the advanced warning area should tell them specifically what to look for or to expect, such as a flagger or a right lane closure ahead. The message ahead is generally used on the warning signs for short term work sites. The overall effect of the signs should make the driver aware of what he or she is approaching and what action will be required. In keeping with the manual on uniform traffic control devices, a rule of thumb for the spacing between signs in a series is 200 feet for low speed city streets, 350 feet for high speed urban roads, 500 feet for rural roads, and 1,000 to 2,600 feet for freeways and expressways. Lightweight yielding or breakaway supports should be used for all sign installations. Sign installations should be reviewed to avoid any possible glare from vehicle headlights. The minimum height requirements for signs attached to posts is shown. Signs on portable supports are required to be at least one foot above the roadway. All signs used at night are required by the manual on uniform traffic control devices to be retro-reflective or externally illuminated. Lighting from existing street lights does not meet this requirement. Favement markings are very important in guiding traffic through work zones. Favement markings, delineators, and channelizing devices outline the traffic path around the work area. Drivers use pavement markings as a primary means of guidance. The standard markings planned for the road should be in place before opening a new facility to traffic. Also if revised lane patterns are planned for the work zone, interim markings should be placed before the traffic is changed. Where this is not feasible, such as during the process of making a traffic shift or carrying traffic through surfacing operations, temporary delineation may be accomplished with lines of traffic cones, other channelizing devices, or short strips of adhesive-backed retro-reflectorized tape. When pavement placed during the day is to be open to traffic at night and permanent striping cannot be placed before the end of the work day, an interim stripe should be applied to indicate to the driver the location of the lane or center line. Channelizing devices are used to warn and direct traffic away from or around the work area. They also control the flow of traffic when separating two directions of travel. They include barricades, barriers, vertical panels, cones, tubular markers, and drums. Each type has distinct visibility characteristics and advantages. The manual on uniform traffic control devices requires that channelizing devices used at night be retro-reflectorized with a material having a smooth sealed outer surface. This includes commercially available retro-reflectorized cheating and tape strips. It does not include the use of pavement marking tape. Some devices are easily knocked down and require a weight, such as a sandbag. These weights must be placed at the bottom of the device for stability and to keep the weight from being thrown if hit. Neither the device nor the weight should cause excessive damage when struck. Sandbags should not be placed where there will be a hazard to the driver or limit the view of the device. Cones are lightweight channelizing devices that may be stacked for storage. They are easy to place and remove and are a minor impedance to traffic flow. For stability, a rubber or sand collar or a specially weighted base may be added. When purchasing cones, specifications may require 60% or more of the weight in the base, thus removing the need for extra base weights or collars. Cones cause little or no damage when hit. They must be at least 18 inches high, but 28-inch cones must be used on freeways and other roadways where speeds are 45 miles an hour or greater. At night, 28-inch cones or larger must be used. 28-inch cones must have a 4-inch wide band, 2 inches below a 6-inch band. Any cone height less than 28 inches is not acceptable for nighttime use. Using cones can have disadvantages because drivers have less respect for them and cones can be easily displaced or knocked over unless properly ballasted. Now, when cones are used, they should be checked periodically and those that have either been displaced or knocked over should be reset. Tubular markers are similar to cones in that they are lightweight, easy to install and or a minor impedance to traffic flow. Tubular markers may be set in special weighted bases or fastened directly to the pavement because of their narrow size they offer a particular advantage when forming new lanes or separating two-way traffic for a short-term activity. Tubular markers are at least 18 inches high with taller devices preferred for better visibility. If used at night, the manual on uniform traffic control devices requires that they be retro-reflectorized. Tubular markers have the same disadvantages as cones, plus having less visible area. Vertical panels are used as either channelizing or warning devices but are not as portable or easy to install as cones or tubular markers. They are useful in narrow areas where barricades and drums would be too wide. Vertical panels should be mounted on lightweight posts, driven into the ground or placed on lightweight portable supports. They may be mounted back to back and used between opposing lanes of traffic. Drums are used as either channelizing or warning devices. They are highly visible, give the appearance of being formidable objects and therefore command the respective drivers. Plastic, not metal, drums shall be used. The manual on uniform traffic control devices requires that markings on a drum be horizontal, orange and white stripes that are retro-reflectorized four to six inches wide. The drum must have at least two sets of orange and white stripes but can have non-retro-reflectorized spaces up to two inches wide between the stripes. Drums must have a minimum width of 18 inches, regardless of orientation, and their tops shall be closed. Plastic drums can be nested, allowing for easy transport and storage. Many of the commercially available plastic drums have watermore flat sides to prevent rolling and have flanges or recesses for warning lights. Barricades should be constructed of lightweight materials and are classified as types 1, 2 and 3. The type is determined by the number of retro-reflectorized rails facing traffic. Types 1 and 2 are portable and can be used for either channelizing or marking hazards. Type 3 barricades are used for road closures. Types 1 and 2 often have rails on both sides and may be used to separate opposing lanes of traffic. The rails have alternating orange and white retro-reflectorized stripes that slope down toward the side traffic is to pass. For road closures, a road closed sign and a detour error sign, if needed, may be mounted on a type 3 barricade. If local traffic will be allowed to use the closed roadway, then the local traffic only sign should be mounted on the barricade. The terms barrier and barricade are frequently confused. A barricade indicates the location of a hazard or a desired path a motorist should take. On the other hand, a barrier provides a positive physical separation between traffic in the work area or between opposing streams of traffic. High-level warning devices are tall portable stands with flags that are visible above the traffic and parked cars. They have a minimum of two orange flags, 16 inches square or larger, at least 8 feet above the roadway. The devices may be used with a sign or flashing light attached, or they may be attached to vehicles used in mobile work operations. Most of the warning lights in use are portable, lens-directed, enclosed units and may be used on channelizing devices, barricades and signs. These are the principle types and uses of warning lights. Flashing lights type A are used on channelizing devices to warn of an isolated hazard at night or to call attention to warning signs at night. High-intensity lights type B are used on advanced warning signs day and night and with high-level assemblies. Steady burn lights type C are used on a series of channelizing devices or on barriers which either form the taper to close a lane or shoulder or to keep a section of lane or shoulder closed and are also used on the channelizing devices beside the work area at night. Both type A and type C lights have photoelectric switches to activate them at night. Warning lights should be secured in such a way that they'll not separate from the channelizing device or sign when hit by a vehicle. Warning lights that come loose during an accident may become dangerous flying objects. Work vehicles in or near the traffic areas are hazards and should be equipped with flashing lights. The vehicle warning may be emergency flashers, flashing, strobe or rotating beacons. High-intensity lights are effective both day and night. The flashing lights should meet the requirements of the agency that has jurisdiction over the street or highway. These lights should be used in addition to other channelizing and warning devices. However, in some emergency situations where the work may be in progress for a very short time these lights may be the only warning device. Arrow displays are signs with a matrix of lights capable of either flashing or sequential displays. They are used for moving traffic out of a lane and may be used at tapered lane closures and with mobile operations. They are not a substitute for the lane closure taper. There are two types of arrow displays. Flashing and sequencing. Arrow displays have four basic operating modes. Left arrow, right arrow, left and right arrow, caution mode. Four lamps arranged in the four corners of the panel. Flashing arrows must never be used on two-lane roadways because traffic may be directed into a head-on collision. Arrow displays on two-lane roads can only be used in the caution mode. Flashing hazard identification beacons are used in work areas both day and night to alert drivers of a critical point in the highway such as a truck crossing and have the same meaning as permanently mounted beacons. Flashing beacons are not used for channelizations. Portable changeable message signs capable of displaying various messages to the motorist will sometimes help construction zone signing. These devices are normally trailer or truck mounted and have their own power system. Because they're expensive to buy and operate, changeable message signs are normally used for the more complex traffic control plans. When using a changeable message sign, be sure the message is clear. A lengthy message may distract the motorist too long. The word order in a message can also cause problems. For example, right lane closed merge would get a different driver response than lane closed merge right. Yet the messages are similar except for the beginning point. This concludes our brief review of traffic control devices. Particular details will be found in the manual on uniform traffic control devices. Now in the following section, we'll be discussing the concepts and elements of traffic control zones.