Proper road tube installation is very important for collecting accurate data with your TRAX. The road tube and the TRAX's air switches comprise the sensing device for the unit. As with all receivers, the sensor has to be functioning properly to record reliable information. With this in mind, examine your installations carefully and be absolutely certain that your unit is recording data as programmed.
Road tubes should be replaced on a fairly consistent basis. Older tube will eventually develop splits that can allow water to enter. When an air pulse is received, this water can be forced back into the unit’s air switch, potentially causing serious damage. Do not risk expensive repair bills by trying to squeezing a few extra studies out of old tube. One rule of thumb is to replace tubes after 30 days of use.
Types of Tube
There are currently two main types of tube that are used for data collection: standard 'O' tube and mini-tube.
Standard O tube is a circular shape tube with an inside diameter of either .25 or .187 inches and
an outside diameter of .60 inches. This tube has been used in the industry for decades with a
wide range of recorders.
Mini-tube is a much smaller and lighter version of standard O tube that has become
very popular in recent years. This tube has an inside diameter of .187 inches and an
outside diameter of .365 inches.
We recommend use of mini-tube for most applications. It is easier to install and use than
standard O tube and testing has shown it to be effective for up to one million axle hits
under normal conditions.
A third type of tube, D tube, is also used for some high speed/high volume applications.
The following installation instructions cover standard O tube and mini-tube. These directions will assist you in placing your road tubes correctly on the road surface with confidence and a minimum of effort.
Recommended Tube Length
Tube length is very critical in order to record accurate vehicle data. The following guidelines should be followed for all studies regardless of simplicity. The lengths listed for each study below have shown to provide the best results based on extensive testing.
L1, L3, L4, L5, L6, L7, L9, L10 (Long tube setups)
To encompass all types of vehicles and speeds, a tube length of 50 to 60 feet is recommended for standard O tube while a length of 40 to 60 feet is recommend for mini-tube. These length should satisfy all requirements for normal street, road, highway and interstate traffic patterns. All tubes used for these types of layouts must be the same length.
L2, L8, L11, L12 (Short tube, long tube setups)
To ensure the pulses from the road tubes arrive at the counter in the proper order, the tube length must be the same from the edge of the road to the counter. This will allow the pulse from the short tube to arrive before the pulse from the long tube. If the A tube (short tube) of a layout has a distance of 26 feet from the edge of the road to the counter, then the B tube (long tube) must have this same distance. In other words, the short tube must be one exactly one lane width shorter than the long tube length.
Example: You are using mini tube to install an L11 layout across two lanes of traffic and each lane is twelve feet wide. In order to ensure that the distance the air pulse has to travel from the edge of the road to the counter is the same for all tubes, you should use 38 feet for the short tubes (A & C) and 50 feet for the long tubes (B & D). The short tubes will be installed over only one lane (12 feet), leaving 26 feet of tube back to the TRAX. The long tubes will be installed over two lanes (24 feet), but since they are 50 feet long, you will still have 26 feet back to the TRAX. It is very important that the air pulses travel over the same distance when two or more tubes are used to record data.
To accommodate the required length of tube, brass splices may be used, if necessary. The splices are approximately three (3) inches long, hollow and do not restrict the flow of air. Do not use the splices on the roadway itself, only on the section of tube after the clamp nearest the TRAX.
Tubes should be placed exactly perpendicular to the flow of traffic to prevent double counting. When using two or more tubes that must be set at specific distances from each other, always use a tape measure or ruler to measure from the center of each tube to determine the proper spacing. In short tube, long tube setups, the short tube should be installed to the zone line (center of the highway). Observe traffic to be sure that vehicles in the outer lane are not coming in contact with the short tube.
Installation - Mini-Road Tube (.187 ID x .375 OD)
Since mini tube is smaller and lighter than standard round tube, less hardware is required to install the tubes. Also, mini tube should not be stretched when installed, just placed on the road.
Webbing can be used to secure the tube at each end of the roadway. You may tie a knot at the far end of the tube instead of using an end plug or PK nail. Since the mini tube is light and low profile, you may use duct tape or two-inch mastic to secure the tube to the roadway.
Generally, three pieces of tape/mastic are sufficient. To reduce wear and/or breakage of the tape, do not install the tape in the path of the vehicle tires.
When installing a short tube, long tube configuration (L2, L8, L11, L12) you may install both tubes completely across the road and tie a knot midway of the half tube. This eliminates nailing the half tube on the center line which can create a safety problem for installation personnel.
Installation - Round Tube (.187 or .25 ID x .60 OD)
Round tube should be stretched one foot for every ten feet of roadway when being installed. Each tube should be secured at each end of the roadway by using a galvanized C-Clamp, Chinese Finger, Figure 8 Grip or an End Plate. Whichever is used, ensure the proper nail size is used. Use the longer nail size (normally 2 1/2 inch or longer) in hot weather due to the softness of the asphalt. In cold weather applications, the asphalt becomes harder, making it more difficult to drive in the nails. In this situation, smaller nails (1 1/2 inch) can be used.
Next, secure the tube on the traveled portion of the road surface by using mastic. As a minimum, one piece of mastic should be placed on the zone line (middle of the road) and two pieces of mastic should be placed in each lane. Additional mastic should be used as deemed necessary to prevent the tube from moving when stuck by a vehicle.