 Transportation engineers tend to talk about the interstate construction days with just a touch of nostalgia and with good reason. There were some huge construction projects, work that called on the very best engineering talents available. The challenges were tremendous. Roadways, ramps, bridges, drainage structures, all in one integrated system. The scale of the interstate network is truly awesome. In comparison you tend to think of today's projects largely reconstruction and rehabilitation as being far less challenging. Right. Except for that one little variation. Traffic. The interstate system was constructed on new right-of-way and most of it was done with no interference from traffic. No wonder there's nostalgia in the air. Virtually all of today's highway work is done adjacent to or in the middle of traffic and high speed traffic at that. Today's construction or maintenance worker spends the whole day trespassing on the driver's territory and that driver doesn't want to give up one inch of the roadway. Doesn't want to slow down either. Getting that driver through a work zone safely is a challenge that matches a lot of those that we faced in the interstate days. Fortunately as a result of research and development over the past decades we have some impressive tools to work with. Standard signs, cones, drums, barricades and the rest. If they're applied with good solid engineering judgment following the standards in the MUTCD the margin of safety is greatly enhanced. This program focuses on just one traffic control device and it's a powerful one. The advanced warning arrow panel commonly called flashing arrow panel. Advanced warning arrow panels are sign panels with a matrix of lights capable of either flashing or sequential displays. In places where the driver's attention might be divided a dozen ways the advanced warning or flashing arrow panel is riveting. The driver's eye go straight to it and the message is clear. Even at night or in bad weather when visibility perhaps more than any other factor determines whether the driver is going to make it to the other end of the work zone. The arrow panel single outstanding message is lane closed ahead. It can be a one lane closure on the right, the left or in the center of a multi lane roadway. Panels can also lead drivers through multiple lane closures left right or center. Lanes are frequently closed by slow moving maintenance operations such as this striping crew. Arrow panels mounted on each vehicle in the convoy force drivers to pay close attention to the potential hazard ahead. And shoulder closures often call for advanced warning as well operating the arrow panel in its caution mode. Although the arrow panel is a highly useful device that carries a strong message and provides good guidance it's not intended to be used alone. It's almost always used to supplement other devices. This program does not deal with all the other devices in the work area. For more information refer to the Federal Highway Administration's Manual on Uniform Traffic Control Devices the MUTCD and your own agency's references. The Federal MUTCD has explicit minimum standards for arrow panels. All state traffic control manuals must either conform with the MUTCD standards or exceed them. This program is designed to help out. It covers the mode selections, design standards, applications and placement standards, costs and equipment maintenance and some general recommendations for operation and usage. First of course the mode selections. Arrow panels should have the capability of the following operating modes or displays. Left flashing arrow. Right flashing arrow. Left sequential arrow. Right sequential arrow. Left sequential chevron. Right sequential chevron. Double flashing arrows. And caution. The caution mode consists of four or more lamps arranged in a pattern that does not indicate a direction. That's usually either four lamps in the corners or the arrow shaft alone. Many engineers prefer not to use just the arrow shaft though, believing that drivers may interpret it as a malfunctioning arrow and may change lanes unnecessarily. If you have any doubt, use the four corner mode. To move traffic to the left or to the right, drivers appear to get the message most clearly through the flashing arrow and the sequential chevron. Those are the preferred displays for left and right side lane closures. So those are the standard mode selections. Sequential or flashing arrows. Sequential chevrons. Double arrows. And the caution mode. Which brings us to the design standards. All arrow panels that conform to the MUTCD's requirements are rectangular with yellow lamps and a flat black finish for good contrast. To reduce glare from sunlight, the lamps have to be either recessed into the panel or equipped with hoods that cover at least 180 degrees. This design makes the display highly visible even in bright sunlight or with distractions in the background. There are three sizes corresponding with three levels of traffic volumes and speeds. Type A panels measure 24 inches by 48 inches. They have at least 12 lamps and must be legible from a distance of one half mile. They're appropriate for low speed urban streets. Type B panels are 30 by 60 with at least 13 lamps and they have to be legible from three quarters of a mile. They're designed for intermediate speed and for maintenance or moving operations on high speed roadways. And type C panels are 48 by 96 with at least 15 lamps legible from a full mile. Type C is designed for high speed, high volume roadways. All of these numbers are in the MUTCD of course along with the other requirements. There's no need to try to remember all the specifics. The minimum lamp on time is 50% for flashing arrows and 25% for sequential chevrons. Those minimums give you the best recognition factor. Both types of arrow panels must be capable of at least 50% dimming from their rated lamp voltage. The panel in this footage is being operated at full power and as you can see it's overpowering. As you get closer it can almost blind you. Clearly that doesn't add to driver safety. In contrast, here's a panel being operated at 50% of its rated voltage. Good recognition, high visibility and no blinding glare. So reasoning behind the dimming requirement is obvious. Although some panels have manual dimming controls, clearly it's best to have the dimmer operated by a photocell. Photocell systems operate automatically, sensing the ambient light and dimming the lamps appropriately. That way no one can forget to turn down the brightness at the end of the day. Now mounting height. The minimum height for all arrow panels is seven feet measured from the edge of the roadway to the bottom of the panel. Now the reasoning here is obvious as well. Maximum visibility even over vehicles driving ahead of you. There's one exception to the seven foot minimum mounting height. It's not always possible to get the panel mounted seven feet up on the back of a work vehicle. For maximum visibility and maximum safety though it should be as high as possible. As you'd imagine the alignment of the panel head both vertical and horizontal has a direct effect on visibility. After all, if you can't see it you can't respond to it. The horizontal alignment is controlled by positioning the trailer. And the vertical alignment is controlled at the panel mount. The goal of course is to make the panel visible from as far away as possible and to keep it visible is drivers approach the work area. Because of the panel's high intensity lights this isn't a precision alignment but the operator should always be trying for maximum effectiveness. The power supplies of arrow panels include diesel, gasoline, solar and batteries. While the MUTCD does not contain any standards for power supplies some state transportation agencies require self-contained power supplies that are capable of running arrow panels for at least 72 hours. Diesel generators are the most commonly used power supply and while some gasoline powered generators are still operated their use should be avoided whenever possible because arrow panels are often exposed to traffic collisions are possible and in an accident diesel fuel presents a lesser fire hazard than gasoline. The use of solar powered arrow panels is becoming more widespread. Solar collectors mounted on the trailer charge batteries that power the lamps. The collection panels should be positioned to catch the maximum amount of sunlight and there should be enough batteries to power the lamps during periods when little sunlight can be collected. Fully charged batteries can run a panel for weeks depending on ambient temperature. Other arrow panels are powered by batteries alone as the batteries are used up they're rotated with recharged ones to maintain a steady power supply. Of course vehicle mounted panels don't require their own power supply they're designed to run off the vehicle's battery system. Okay so those are the design standards. Now applications and placement situations best suited to the use of an arrow panel and where to place it for best results. As I mentioned earlier the arrow panel's overriding message to drivers is lane closed ahead. Research has shown that drivers start preparing to merge as soon as they see an arrow panel. Lane closures then are the single most suitable application but not to close one lane of a two-lane two-way road. Clearly if you close one lane of a two-way road by using a flashing arrow drivers could be guided into the path of oncoming traffic. Arrow panels are primarily suited for use on multiple lane roadways. When an arrow panel is used in conjunction with channelizing devices it's always best to install the panel off the roadway at the beginning of the taper on the shoulder if possible. Granted the panel isn't directly in line with the driver's eye but the message is still clear and you have to remember that the panel itself is a potential collision hazard so it's best to keep it out of the way. For a single lane closure a transition taper of length L is formed with channelizing devices. L is determined by using one of two formulas given in the MUTCD. This is followed by a buffer space of sufficient length to give the driver one last opportunity to bring his vehicle to a stop before entering the work area itself. The buffer space and the work area are outlined with a series of channelizing devices. Finally the arrow panel is placed in its standard position at the beginning of the transition taper. In a multiple lane closure most transportation agencies run the standard taper length L to close one lane then a tangent section of 2L to allow traffic to stabilize then another taper L to close the next lane and a tangent section running past the work area. An arrow panel is placed on the shoulder at the beginning of the first taper and a second panel is placed in the lane that was closed first at the beginning of the second taper. For the center lane work area shown here first the left lane of the roadway is closed an arrow panel is placed on the shoulder at the beginning of the lane closure taper. A standard taper length is set up followed by a tangent section of 1.5L then the traffic is divided allowing the right lane of traffic to pass to the right of the work area and the left lane of traffic to pass to the left of the work area. The center lane is closed with channelizing devices as shown an optional panel displaying a double arrow can be placed toward the back of the taper that way the trailer fits well between the rows of channelizing devices and the panel itself doesn't encroach on the travel lanes. Frequently space is simply too limited to put the panel off to the side of the closed lane where it should be. Here for example moving the panel to the right would place it on the sidewalk among the trees so as the next best placement it's been positioned as close as possible to the beginning of the taper behind the channelizing devices placement at the start of the taper is always preferred over placement in the middle of the taper so that's the general rule either on the shoulder at the beginning of the taper or behind the channelizing devices as close as possible to the beginning of the taper but the real world isn't so neatly defined as that no two worksites are identical and the overriding rule is visibility if drivers won't have enough time to see the panel and react to its message make adjustments. Here's a quote from the MUTCD placement of the arrow panel should be varied as needed to achieve recognition distances so with hills curves or other obstructions reduce that desired recognition distance the panel can be moved upstream by as much as 2,500 feet if the panel must be moved upstream try to locate it on the shoulder not in a traveled lane if there's no space on the shoulder at that point you should probably consider bringing the taper upstream as well and extending the lane closure another problem to watch for is the potential for confusion with nearby ramps median crossovers and intersections take a close look at all the possibilities how will drivers react to any single placement are you giving them the positive guidance they really need would a minor adjustment produce the effect you want lanes are frequently closed by mobile construction or maintenance operations pavement recycling patching and so on the arrow panel mounted on a vehicle at the back of the operation uses the same panel displays as would be used for a stationary operation a flashing right arrow for left lane closures a flashing left arrow for right lane closures and a double arrow for center lane closures when arrow panels are used for shoulder closures they should be operated in the caution mode not as a flashing arrow the flashing arrow tells the driver to move over and shoulder closures don't call for a reaction just for heightened attention so those are the major applications in placement standards for single lane closures multiple lane closures center lane work areas and shoulder closures now some agencies use arrow panels for another application traffic diversions or shifts but since an arrow panel is mostly understood as indicating a lane closure it should be used in a lane shift situation only after an engineering study justifies its use now costs and maintenance as you'd expect with a fairly complex piece of equipment arrow panels don't come cheap truck mounted panels depending on their size cost something like 750 to $2,000 and you have to remember they run off the trucks generator so they don't have a special power supply trailer mounted arrow panels with generators cost about $5,000 most engineers tend to agree that given the increased effectiveness in terms of traffic control and traffic safety $5,000 is a bargain but bargain or no bargain $5,000 is an investment and that investment has to be protected through regular scheduled maintenance like any other traffic control device especially in work zones arrow panels need attention periodically of course all engines need oil changes and so on and the generator for an arrow panel is no different but in this program we're concerned only with the maintenance work that affects the operating effectiveness of the arrow itself that is maintenance that affects traffic safety first naturally that means the lamps and lenses the traffic control supervisor should frequently check the display to see that all lamps are lit replacing lamps may appear to be an unproductive chore but an incomplete arrow is an incomplete message to the driver given the time and cost invested in installing an arrow panel there's just no reason to settle for less than 100 percent effectiveness road grime is a concern in all work areas and depending on the road conditions the arrow panels effectiveness can be reduced by 50 percent or more in a short period of time lenses should be cleaned on a regular schedule and the cleaning should be more frequent if road conditions indicate a reduction in visibility as i mentioned earlier many arrow panels are equipped with photo cells to automatically dim the lamps at night you have to remember that photo cells aren't fail safe they should be checked on the same schedule as the other maintenance items if the sensing element is caked with road grime the dimming can be actuated during daylight hours and of course if it's defective it should be repaired or replaced the amount of dimming required can vary a good deal from one location to the next as you'd imagine the ambient light in a brightly lit urban area is quite different from the light on a remote rural highway the best test is a nighttime drive through the work zone the first night the panel is installed with adjustments made on the spot the flashing frequency rarely needs adjustment just check now and then to see that the display runs at 25 to 40 flashes per minute for most projects one person should be in charge of maintaining the arrow panels on panels that have their own generators very little is likely to go wrong between refueling but every time the tank is filled the operator should give the whole unit a good look lamps lenses dimming controls and so on panels without generators should be checked at least every few days same items and in any case all project personnel should be encouraged to watch for problems and report them as soon as possible like all other traffic control devices an arrow panel can be highly effective or practically worthless well now that we've covered mode selections design standards applications and placement standards and costs and maintenance here are the key recommendations first make sure that all mutcd standards are satisfied as a minimum then refer to your own agency standards don't use arrow panels to close lanes on two lane two-way roadways the potential for misguiding traffic is just too great whenever it's possible place arrow panels on the shoulder at the beginning of the taper if there's no shoulder or not enough space off the roadway place the arrow panel as close as possible to the beginning of the taper behind the channelizing devices where sight distance is limited consider using a supplemental arrow in advance of the work zone or extend the lane closure upstream to a point where visibility is acceptable if multiple panels are being installed the spacing between them should be at least three times the taper length l found in the mutcd and nevertheless than a thousand feet closer spacings tend to overpower drivers and they can react erratically if a double arrow seems warranted watch the traffic movements immediately after installation if it causes confusion make adjustments or remove it and finally enforce all requirements for dimming the lamps at night drivers who are blinded as they pass an arrow panel simply can't be expected to react safely arrow panels are relatively new traffic control devices the research and development efforts are far from complete given our relatively short experience with them we basically know just two things in the right situation the expense really is a bargain and in the wrong situation or if they're not placed and operated with care they can cause more problems than they solve the flashing arrow panel it's a powerful device not to be taken lightly