Q1. – Is a K or Ka-band radar device on the IACP’s approved list important?
A1. – Ka-band requirement combined with IACP listing requirement reduces choices to, perhaps, 1 manufacturer in the US. Every sign manufacturer in the U.S. but one uses one of two guns; Decatur Electronics SI-II or Kustom Signals’ DRU unit. Both of these are K-band units designed expressly for this type of application but both of no interest to the folks compiling the IACP list. Unless the client expects to write tickets and issue fines for offenses using these signs (not recommended either) this requirement is competition limiting, over-reaching and costly. These types of signs are described by both the NHTSA and the MUTCD as “advisory” signs and not “traffic control” devices negating any reason to over-engineer such a product.
Q2. – The sign we are considering has what they call a 7-Segment display. They say these are as good as your full graphic characters? Are they really?
A2. – The seven segment style design is simply antiquated. Moreover, independent studies have shown that cognitive recognition of seven segment vs. full graphic characters is significantly slower and at X-whatever mph, time is of the essence. This independent study also demonstrates that our 18″ graphic display outperformed one competitor’s 25″ character sign in live on-road testing. The most recent revision of the California MUTCD specifically recommends use of full graphic characters over 7 segments when selecting a speed feedback sign.
Q3. – What do you think of user adjustable amperage (sic. Intensity) for different applications?
A3. – There are no different applications; every time you place one of these signs in public you are trying to slow people down. Adding this variable is only going to exasperate anyone looking for consistent results. Now, automatic adjustment to ambient light conditions is critical as you need full intensity in full sun and need to moderate brightness for night conditions.
Q4. – One supplier is touting the advantage of a rather limited (30 degrees) included angle of readability. RU2 talks about 160+ degrees of legibility. What gives?
A4. – This 30 degree thing is like a religious question; you either believe or you don’t. But once you do the trig, it smells more like a red herring. Here is our take:
IF you calculate the distance from the center of the sign face, accepting that the near lane driver is something like 14 ft. lateral off-set and intersect the driver with the 30 included angle the sign goes dark for him about 52 ft. down range. If you open that up to 160 included angle the sign goes dark about 2½ ft. down range –let’s call it a 50 ft. delta. 50 feet at 35 mph is covered in less than 1 second, at 25 mph in 1.36 seconds. What we are suggesting here is that the entire argument is…an excuse, not a feature.
Q5. – Regarding the radar device, they talk about programming the sensor for distance and inclusion/exclusion of approaching/receding targets. Huh?
A5. – The second part is easier to address so we will start there. Oddly enough there are few suppliers out there still providing base equipment without single directional (approach only) radar, making it instead an option that you have to pay for. Our gun can pick up 8 discrete targets, determine approach/recede and, sort by signal strength. And we don’t charge extra, so there! We specifically filter for the strongest, oncoming target –only. Under what circumstances would you want to display receding targets other than to confuse everyone looking at the sign?
Programming for distance, not so easy. Our original response was to make the sensor independently adjustable of the sign face in both X and Y axis so that the sensor paints an “area of interest” much like pointing a flashlight while keeping the sign’s “best face forward”. This is in contrast to being able to make the sensor “stupider” but still pointing at the moose on the horizon.
RU2 recently added user adjustable sensitivity to our signs in 5 increments for the greatest degree of flexibility in set up. The Range or Range Sensitivity setting is a non-linear adjustment. The biggest factor is actually the target size and its reflectivity. A truck with a big front end will be more reflective than a sedan or sports car. Also, as some may assume, the range sensitivity adjustment does NOT change the radar power output. It’s a signal to noise ratio adjustment. It actually adjusts the level at which we recognize a target above the noise floor. For example, when the radar is set to full signal level of 5, it is most sensitive, or would measure targets at the greatest range. Easily a ½ mile with the DRU-III and your typical sedan. If you select 4, then the signal has to be higher above the noise floor, or stronger before we measure/display the info. Likewise down to 3, 2, and 1. But to say the radar will pick up a target at 100 ft. or 500 ft. at a level of 1 would be highly dependent on the target and the environment. We attempt to make the signal detection like the following percentages;
5 = 100% 4 = 80% 3 = 60% 2 = 40% 1 = 20%
However, this will never equate to a linear range scale.
You can also use the Squelch analogy for a radio. The signal has to be stronger on a radio as you turn the range level down.
Q6. – Suspensions: Leaf Spring vs. Torsion Bar; what’s the difference and should I care?
A6. – At the loaded weights we are talking about (1000 pounds is a trifle in the trailer world) the biggest difference between the two technologies is a bit nicer ride (torsion) versus bullet proof (leaf). You may have to replace a torsion bar suspension over the life of the trailer; you probably won’t have to replace a leaf spring. We went with bullet proof leaf springs; some of our competitors went torsion claiming a gentler ride for their (tender) electronics. So, should you care? Nope.
Q7. – What’s the deal about wet paint versus powder coat and can you do either right or wrong?
A7. – Without a lot of hot air (get it?), a properly applied powder coat finish will outperform any wet paint finish. Today, you will find wet paint finishes only on the cheapest of equipment and we don’t mean just radar trailers. And sometimes that’s alright if the life expectancy of the piece of equipment is short by its nature (think: arrow boards).
We employ a 2 part powder coat system, first applying what is known as “high zinc” epoxy primer which gets a partial bake, then a polyester application over that. Epoxies alone are very chemical resistant, great adhesion and impact resistance but typically have very little resistance to UV rays and will “chalk” very fast leaving a dull, smudgy, unattractive finish. Polyesters by themselves don’t have the chemical resistance of epoxies but are specifically formulated for outdoor equipment and have strong UV resistance, staying bright and shiny for years. Dirty metal, sharp edges and under or over curing are the enemies of a good powder coat. Great prep and attention to process detail prevent that.
Q8. – While we’re on paint, are any coatings really “graffiti proof”?
A8. – No, not really. What we have been told by the manufacturer we use (Rohm & Haas) is that the only Graffiti-proof coating is a secondary clear overcoat which, unfortunately, due to a difference in coefficient of expansion, will craze (crack) and trap dirt, eventually causing the “object of concern” to look like crap anyway. And it’s expensive. We can do it. We don’t recommend it.
Q9. – Batteries, batteries, batteries…what should I know about batteries?
A9. – Quite a bit, yet nothing…how Zen! There are really two questions here; one, what is the difference in battery technology and two, how long can I go with your equipment between charges?
Our battery universe is divided along the lines of battery construction. Currently, there are three common lead-acid battery technologies: Flooded, Gel, and AGM.
Flooded or Wet Cells are the most common lead-acid battery-type in use today. They offer the most size and design options and are built for many different uses. Typically, the cells can be accessed via small ~1/2″ holes in the top casing of the battery so the user can replenish any electrolyte the battery vented while charging the battery.
The plastic container used for flooded cells will have one or more cells molded into it. Each cell will feature a grid of lead plates along with an electrolyte based on sulphuric acid. Since the grid is not supported except at the edges, flooded lead-acid batteries are mechanically the weakest batteries. They are also the cheapest.
Gel Cells use a thickening agent like fumed silica to immobilize the electrolyte. Thus, if the battery container cracks or is breached, the cell will continue to function. Furthermore, the thickening agent prevents stratification by preventing the movement of electrolyte.
As Gel cells are sealed and cannot be re-filled with electrolyte, controlling the rate of charge is very important or the battery will be ruined in short order. Furthermore, gel cells use slightly lower charging voltages than flooded cells and thus the set-points for charging equipment have to be adjusted.
Absorbed Glass Mat (AGM) batteries are the latest step in the evolution of lead-acid batteries. Instead of using a gel, an AGM uses a fiberglass like separator to hold the electrolyte in place. The physical bond between the separator fibers, the lead plates, and the container make AGMs spill-proof and the most vibration and impact resistant lead-acid batteries available today. Even better, AGMs use almost the same voltage set-points as flooded cells and thus can be used as drop-in replacements for flooded cells. Basically, an AGM can do anything a Gel-cell can, only better. However, since they are also sealed, charging has to be controlled carefully or they too can be ruined in short order.
Gel and Absorbed Glass Mat batteries are relative newcomers but are rapidly gaining acceptance. There are some very compelling reasons to use VRLAs (valve regulated lead acid):
•Gel and Absorbed Glass Mat (AGM) batteries can dispense charge at a higher rate than flooded cells due to their lower Peukerts exponent. Deep-cycle Flooded Cells cannot deliver more than 25% of their rated amp-hour capacity in amps without plummeting Available Capacity.
•Virtually no gassing under normal operating conditions: Unlike flooded cells, gel cells and AGMs are hermetically sealed and operate under pressure to recombine the oxygen and hydrogen produced during the charge process back into water.
•For every additional 15 degrees of heat over 77 deg F, lead acid battery life (regardless of type) is cut in half (batteries self-destruct with time, you can only slow that process).
•VRLAs can operate in any orientation (although you may lose some capacity that way) and even if a container is broken, a VRLA will not leak. Proper (heavy duty) battery restraints are a must, regardless of battery type.
•Gel cells and AGMs require no maintenance once the charging system has been properly set up. No equalization charges (usually), no electrolyte to replenish, no specific gravity checks, no additional safety gear to carry in order to protect yourself. If you want to be anal retentive about VRLAs you can load test them. However, proper charge control and protection is much more important with VRLAs because once fried it is impossible to revive them.
•The higher charge efficiency of AGMs allows you to recharge with less energy: Flooded cells convert 15-20% of the electrical energy into heat instead of potential power. Gel-cells lose 10-16% but AGMs as little as 4%. The higher charge efficiency of AGMs can contribute to significant savings when it comes to the use of expensive renewable energy sources (wind generators, solar panels, etc.) as your charging system can be 15% smaller (or just charge faster).
•While flooded cells lose up to 1% per day due to self-discharge, VRLAs lose 1-3% per month.
•High vibration resistance: The construction of AGMs allows them to be used in environments where other batteries would literally fall to pieces. This is another reason why AGMs see broad use in the aviation and the RV industry.
RU2 uses gel cells on its Fast-6000 and Fast-600 models, AGM on everything else. Enough about that!
The other issue, probably more germane, is field autonomy or, how long can I deploy the trailer between charging. Everything else being even, the two primary factors in play are current draw of the gun and sign and duty cycle. Overall efficiency of the design can vary all over. RU2’s primary 12”and 18”character signs draw 18 Watts peak, another manufacturer may be at 25W, another even higher. The difference between 18 and 25 is a 28% advantage right there. We typically see 7 to 10 days of service from a fully charged trailers and under proper circumstances, many of our solar assisted trailers are virtually field autonomous requiring quarterly of semi-annual charges to “top them off”. Amp hour figures are by themselves meaningless.
Q10. – The “SPEED LIMT” sign size on your Fast-375 isn’t dimensionally to MUTCD standards. Are we going to be in violation if we use it?
A10. – Regarding the “non-standard”sizing of the Fast-375 sign overlay, it stems primarily from the origin of the underlying electronics. That is, early on we decided to make the best “full graphic”character sign we could at standard 18”character size for placement on a radar trailer. This was long enough ago that the pole-mount concept hadn’t been marketed by anyone yet. As we were not looking to reproduce or adapt to anyone’s standard sheet metal we started out with a blank sheet of paper and ended up with a terrific sign with a 40”wide case.
Designing the typical R2-1 Speed Limit Sign overlay for the nearest standard size (36”x 48”) we maintained the 1 to 1.33 aspect ratio and ended up with a 41”x 54.5”plaque. Non-standard perhaps, but conforming.
An interesting thing comes up in all of this and is particularly poignant if one was examining “standards”for a reason “Not To Do Something”; The 18”character specification (or 12”for that matter) defies all R2-1 standards. The standard character heights are 8”, 10”, 14”and, 16”. The 16”character is for the 48”x 60”sign, recommended for posted limits of 55MPH or greater. Strictly by these standards everyone in this business is wrong. An 18”character on a 36”x 48”(or larger) sign should look really stupid (and non-conforming) except…that it doesn’t. And our characters look really good in our plaque.
By the way, in looking for 3rd party blessings, the most recent California MUTCD issued this: “Guidance: To the degree practical, numerals for displaying approach speeds should be similar font and size as numerals on the corresponding Speed Limit (R2-1) sign” which we naturally take as a ringing endorsement of our “full graphic characters” (vs. antiquated 7 segment).
Q11. – We are in the process of writing specifications for the purchase of a radar speed trailer. One of our engineers is concerned with NCHRP 350 compliance as we intend to use it on an Interstate. What’s the scoop?
A11. – Trailers of this type are exempt from NCHRP – 350 Crash Testing. Even though they are a Type IV device, the FHWA has recognized that in order for them to meet NCHRP-350 requirements – they would need an Impact attenuator that would be bigger than the Trailers. Additionally in an attempt to make Changeable Message Signs (Full Size Trailers) NCHRP-350 compliant (in past testing), the “Roll Ahead” factor encountered after impact was unpredictable. In other words – you couldn’t tell if the impact attenuator made the unit safer – more often than not the Trailer would still roll forward further than an unprotected trailer and often would wind up crossing adjacent lanes of traffic.
It was decided that trailer mounted equipment would be compromised by an attenuator in that it would be heavier, take up a larger footprint on the roadway, and present an operational problem in its field deployment (make it more complex to setup and remove from the roadway – resulting in Longer exposure in live traffic to the user).
After checking accident statistics (Nationwide) the FHWA could not find a number of reported accidents of Vehicles running into the trailer mounted equipment (Other than a few anecdotal occurrences of Drunk Drivers hitting trailers).
Their final decision said that the practices currently being used (putting the trailers behind guardrail and barrier walls where practical,or in the clear way – described as 30 feet off of the traveled portion of the highway, or if need required that the unit be placed on a shoulder, then the unit should have at least 1-2 feet of clearance to the live lane and it should have temporary traffic control devices – that is orange drums or cones used to form a taper in front of the trailer to highlight the placement of the trailer on a shoulder.
Q12. – Okay, that’s great but, how about NCHRP compliance and the Pole Mounted products you offer?.
“I spoke to you yesterday about the “ABC” Department of Transportation requirement that these signs must meet”crash-worthiness” as defined in the National Cooperative Highway Research Program Report 350. You indicated that these devices are exempt from that requirement, and you have a copy of some literature you could send me on the subject.”
A12. – “My bad” on this, to a point. The Report 350 exemption is for Category IV, trailer mounted devices – please see A11 above. However, the FAQ’s for Sign and Luminaire Supports would indicate that the burden of testing is not on the “mounted object or device” as it is on the support structure itself. Please see excerpt below, link to original source provided (red highlight mine).
Q: WE WANT TO ADD LIGHTS, A BATTERY, AND A SOLAR PANEL TO OUR SCHOOL ZONE SIGN. DOES THE COMBINATION HAVE TO BE CRASH TESTED?
A. There are four factors that determine the acceptability of breakaway supports:
- Stub height (Must be 4 inches or less. As this will not change with the addition of auxiliary hardware it will not be discussed further.)
- Vehicle velocity change / occupant impact forces. The addition of flashing lights and solar panels or other auxiliary equipment will not likely affect the change in velocity experienced by the vehicle or its occupants unless it becomes substantial compared to the mass of the pole. Additional hardware attached at or above the sign will raise the center of gravity of the system slightly but since it is away from the base the breakaway features will still perform as intended. The overall mass of the pole, sign, and auxiliary equipment should not exceed 600 pounds .
- Windshield penetration. Windshield damage was not a formal pass/fail criterion under the 1985 AASHTO Sign and Luminaire spec and we did not change this when we adopted Report 350 in 1994. However, windshield damage will be pass/fail evaluation criteria under the AASHTO MASH. If the auxiliary hardware is at or above the sign, the effect should be minimal.
- Roof crush. Roof crush up to 5 inches was permitted under NCHRP Report 350, but very few sign installations even approached that amount. (Luminaire poles weighing 1000# or more could easily fail this test.) The addition of more hardware could increase the risk under low speed impacts, but roof crush can be controlled by following the 600 pound weight limit mentioned above. Under MASH, roof crush will be limited to 3 inches maximum.
Safe placement of these types of devices on the sign also depends on the structure of the sign, the sign height, the type of vehicle impacting the sign, and the breakaway nature of the sign support when it is impacted. The conditions outlined above assume the sign pole is rigid and that the pole itself will not deform upon impact. Also the breakaway feature must be a slip base, frangible coupling system, or a cast aluminum transformer base – “base bending or yielding” systems such as u-channel posts, perforated square steel tube posts, or composite posts require full scale crash testing.