Introduction
As much as some people believe that loops are going away, the fact is loops are still being installed and at a greater number than ever. The technology has not changed significantly, and all the other technologies as great as they are still compare themselves to loops. Why is that? Loops are still very accurate and very reliable when installed correctly.
Loops technologies are evolving; and although they may not be flashy, technologically advanced, or wiz-bang, they still get the job done and at a level of reliability and accuracy still not achieved by other technologies.
Problem Statement
Due to changing attitudes for Green Awareness which includes increased bicycle travel to work, rapid transit use, and public transportation, the Traffic industry is adopting new ideas for traffic control. There are new requirements and regulations that the traffic industry is developing to promote safer operations at the intersection for bicycles and pedal powered vehicles.
There are also needs for the ability to identify vehicles for TSP / LRT amongst normal traffic also known as Automatic Vehicle Identification. With all this, the need for reliable detection is still paramount.
Previous Options
Loops were always about detecting vehicles. For over 40 years loops have been in the ground and detecting vehicles very well. There are a lot of variations between these vehicles from Scooters to Semi Tractor trailers and everything in between.
Bicycles have not been inas much focus to recognize mostly because they tend to ride on the side of the road and that the population of bikes vs. other vehicles was extremely small. Normally,bicyclists only got the green lights when other vehicles were present. Push buttons were another option but very inconvenient to the bicyclist.
There has not been a big need to identify vehicles independently, except the occasional fire vehicle or ambulance than needs preemption at an intersection. This has been done for years using sophisticated and expensive equipment. Now add to the mix, busses, Light Rail, Rapid Transit, and other forms of mass transit, and there is a bigger need to identify these vehicles accurately and inexpensively.
Loop installation has been done the same for years with the same equipment and hardware with little advancement. When done right the loop can last the lifetime of the roadway. However, this has always been a point of concern and failure when it comes to loop detection. What most people don’t know is that it is a very rare occurrence that a loop “fails” on its own.
Most cases of loop failure are due to contractor’s digging up a loop, or failure of the roadway itself, and on occasion poor installation practices.
Solution
This paper will follow the three ideas listed above and provide solutions to each challenge; bike detection, Automatic Vehicle Detection, and loop reliability.
Bike Detection
Bike detection in loop detectors has really always been around. The problem is that the sensitivity of the loop has to be set so high to properly register a bike that it can cause the loop to “cross talk” or interfere with an adjacent loop, or pick up vehicles in adjacent lanes. This creates issues for most detectors.
California was one of the first states to adopt legislation to insure that bikes can be detected at all intersections that use detection, otherwise the intersection must be put into recall or be fixed time.1 On top of this there is a need to differentiate between a bicycle and other vehicles.
Traffic Engineers are requiring additionaltiming parameters to their intersection to specifically handle bicycle needs. The Controller manufacturers are adding “bike timing” to their controller meet this need. Now detection manufactures have to come up with a way to determine a bike is at the stop bar and not a motor vehicle.
Bike detection with loop detection has been available for several years using amplitude of a signal to determine a bike versus a car or larger vehicle. But, it is not so accurate against a scooter or small motorcycle. However, with increased processor power the capability of signature recognition now allows the detector to distinguish between a bicycle and a scooter or motorcycle very reliably.
The development of the C1101-B and C1201-B detectors by Reno A&E2 has included this technology into its latest line of loop detector. The signature of a bicycle is very distinct, and when it is recognized, and only when a bike is recognized, will the detector output a call.
The detector also has internal “bike minimum time” and “bike extension time” settings so that the bicyclist will be insured enough time to cross the intersection, and addition bikes will get continued greens if needed, up to the maximum time allowed. To do this a specially designed loop configuration is needed and a preform loop is highly recommended for accuracy. (See benefit 3).
The loop that is used for detection of bikes is a parallelogram that is set at a 45 degree angle to the direction of travel and has a leading edge-trailing edge distance of 42 inches. This design accentuates the signature of a bicycle and is a key to the operation of this detector. The installation can be anywhere in the intersection to accommodate existing loop installations.
Set up of the detector has been simplified to just 4 parameters that are configured from the front panel of the detector card. Once the detector is set up it needs no maintenance and no further adjustments.
AVI – (Automatic Vehicle Identification)
There are several applications in traffic that require or would benefit from Automatic Vehicle recognition. These include: priority service (TSP), gate access, and check-in / check-out detection.
While the first has been done for years with the use of optical detectors, there are increased needs for precision detection of these vehicles. Determining when a bus or transit vehicle is entering or leaving a bus station can’t be accurately assessed with optical devices. GPS can do this but is a very expensive alternative. What are the alternatives?
Again, the solution is a loop detector specifically designed to pick up a small inexpensive device on the vehicle that transmits a code. This code could be unique to a department or can be unique to a vehicle. Once the detector is programmed to recognize the code, then anytime that vehicle is detected the detector outputs a call as needed. The Model AVI-E from Reno A&E can be programmed to accept.
This beneficial functionality can be used to open gated communities for emergency and other public service vehicles, be used for inputs into traffic controllers to adjust cycle lengths and timing for busses, Light rail, or even heavy vehicles that need more time to accelerate or stop.
Preformed Loops
The key to the success of all loop detection is, of course, the loop. New technologies in materials and manufacturing have made significant leaps in this area. What used to be needed was heavy gauge wire and thick insulating jackets to withstand the stresses of installation and hazards of the road. Now with the lighter more durable materials the loop can be made more durable and less bulky. Another increase in reliability and performance can come from using preformed loops. Reno A&E has several different versions of loops including PLBs, PLCs, and PLHs4 all of which will meet any installation requirement.
Preform loops can be laid into saw cuts, or can be laid after milling prior to a new asphalt layer is applied or can be laid in the sub-base in new installations. Each type of installation requires a different preform loop, all of which can be specifically designed and supplied to contractors as needed.
Preformed loops have the advantages over standard loops in several areas:
1. First they are made in a controlled and regulated environment using a very precise process to insure that each loop is working correctly.
2. Testing is performed before the loop is shipped to insure that it is ready to go into the ground.
3. The home run is included to make sure that no splices are required between the loop itself and the cabinet.
4. Encapsulation with a water repellent gel of all splices and cable within the protected sheath guarantees that no foreign materials will corrode or degrade the loop after installation.
5. Multiple layers of the material XLPE (Cross-Linked Poly Ethylene) also creates a strong protective boundary.
6. The winding of the loop is encased in one protective sheath which has additional benefits in that the individual wires will not move relative to each other. This is one of the major causes of failure in normal loops.
Failures of loops occur, naturally, when pavement shifts occur and cause individual winds of the wire to shift relative to each other. This shifting of the pavement can cause stretching and cracking of the insulation thus causing water and other foreign materials to invade the wire corrupting the installation. The preform loop with its added protective covering and barriers helps protect against this, increasing the longevity of the loop.
Other failures are due to uncontrollable circumstances such as accidental incursions from back hoes, ditching equipment and other contractor mishaps. These can be repaired and if done right will not affect the loop operation.
Implementation
A complete system should be used when using loop detection. Just as with any detection system, the right installation and right equipment should be used at all times.
Installing video detection and not using the approved camera is never an option. Why would a loop detector be used without the right loop? All the components are necessary to make sure that the detection is maximized for both reliability and accuracy.
Choosing the right detector for the job whether it is for standard vehicle detection, bike detection or Automatic Vehicle detection is important. Choosing the right loop to go with that is as equally important.
If it is going into a saw cut, then the solution would be to use a PLB preformed loop. If it is going under a new layer of asphalt overlay, a PLH is more suitable. If it is going underneath a new installation, the best solution is a PLH-R is used for direct burial.
With each installation the right loop configuration is also necessary. Bike detection in a bike lane or in a left turn lane should be designed to optimize the bike detection with the parallelogram designed loop. Placement for bike loops and AVI loops is critical to make sure the detection of the appropriate vehicle is where it needs to be.
Surveying and planning are important. Make sure that both are used to determine where the best place for the loop is going to be. The use of plans is not enough to determine where the loops will be needed.
On top of all the hardware and software and installation, training is most important. Properly trained loop crews can install loops in relatively short periods of time. In most cases loop crews are not available, so training should be a part of any project to make sure that the installation is done correctly. There are a lot of myths about loop installation that can make the installation harder than it needs to be, and more costly in the long run.
Summary
Loops have been around longer than any other current form of detection. The gold standard for accuracy is still a loop detector. With the increase in technology such as faster processors and communications, and more advanced materials, loops are seeing some resurgence. There are new features in the old reliable loop detector that are worth looking at again.
Automatic vehicle detection and Bike detection are just a couple of the new technology features that are beginning to be available with more to come as newer, faster processors are utilized. Add to this the added reliability and increased life expectancy of a preformed loop. With this combination of functionality and reliability within the full loop detection system, it easy to see why loops have not gone by the wayside as many of the competitive products predicted so many years ago.
1. (TOPD 09-06 / California AB1581, 2008)
2. C1101-B / C1201-B Series
3. AVI-E (multiple codes)
4. Preformed Loops
