On October 16, 2007, I gave a presentation, "Detecting Bicycles and Motor Vehicles Using the Same Loop Detector" to 3 members of Caltrans HQ Electrical Systems Branch: Theresa Gabriel, the head of the branch; David Maurin and Bashir Choudry. I recently sent most of you an article with what I intended to present, asking for comments. Thank you to those of you who provided input; it was quite valuable.
After my presentation, Ms. Gabriel responded to my recommendations for changes in the Caltrans Standard Plans, Standard Specifications, Transportation Electrical Equipment Specifications, and the California MUTCD that would address problems that bicyclists are having being detected at actuated traffic signals in the State.
Here are my recommendations followed by Ms. Gabriel's responses:
1. Configure the head loop as a diagonal quadrupole
Caltrans has no interest in investing any additional time or money into improving loop detection. Loops are an obsolete technology that are not reliable for the detection of bicyclists. Furthermore, Construction and Maintenance personnel at Caltrans complain that loops result in premature pavement failure, particularly in asphalt concrete pavement. Therefore Caltrans is looking to non-invasive technologies for detection at actuated traffic signals. Caltrans has contracted with PATH at the University of California, Berkeley, to develop this new non-invasive technology. Any new detection method, however, would need to be compatible with Type 170 controllers (and presumably 332 cabinets) and be able to hold the call as long as the bicyclist was stopped.
Caltrans is interested in bicycle detection and Ms. Gabriel said that she had been actively involved in the development of AB 1581 as well as unsuccessful versions of the bill in earlier legislative sessions.
Caltrans also has problems with insufficient funding to maintain the approximately 5000 traffic signals that it currently has. Caltrans cannot afford to upgrade its traffic signals to meet ADA standards, much less to detect bicyclists. Currently, Caltrans will install one or more Type D bicycle loops at a new or rebuilt traffic signal only if bicycle traffic is anticipated. But even when a Type D loop is installed they still receive complaints from bicyclists. Only bicycle pushbuttons are guaranteed, and they are not practical. Any new detection method will need to guarantee that all bicyclists are detected, including those who are riding non-metal bicycles or from children whose bicycles have small wheels.
2. Locate the loop where bicyclists are expected to stop, but if this is not possible, use a Bicycle Detector Symbol
Ms. Gabriel feared that making a bicycle loop larger in order to locate it where a bicyclist is expected to stop would result in detection of vehicles in the adjacent lane and crosstalk with loops in the adjacent lane. Caltrans is not interested in investing any funds into finding out whether larger bicycle loops have the problems that she fears.
Even with a Type D loop, bicycle detection is not guaranteed to be reliable. Caltrans is unwilling to use Bicycle Detector Symbols unless reliability can be guaranteed, because if a bicyclist stops over a Bicycle Detector Symbol and is not detected and proceeds on a red signal and is injured or killed in an accident, then Caltrans could be held liable.
Besides, the decision to install Bicycle Detector Symbols at actuated traffic signals and whether to add Bicycle Detector Symbols to the drawing in the California MUTCD showing bicycle loop locations lies with the Striping Branch within Traffic Operations, not the Electrical Systems Branch.
3. Use elastomeric loop sealant (or perhaps hot-melt rubberized sealant)
Ms. Gabriel said that the major cause of loop failures was pavement failure, not loop sealant failure as I had stated.
Caltrans has stopped using asphalt emulsion and epoxy loop sealant. It used to supply a 2-part elastomeric loop sealant to construction contractors, but now specifies only hot-melt rubberized asphalt. Although 3M loop sealant is a 1-part sealant and is likely considered elastomeric, Caltrans is unwilling to specify products that are only available from a single source.
Besides, the Transportation Laboratory is in charge of the loop sealant Standard Specifications, not the Electrical Systems Branch.
4. Connect the loops in series
Caltrans uses parallel-series connections not to reduce the inductance at the input into the loop sensor (as I had speculated) but to eliminate the need for a trouble call when a single loop fails out of a group of four. Given the lack of funds, however, Caltrans cannot afford enough traffic signal technicians to perform routine maintenance on detector loops or the equipment inside signal cabinets, so the failed loop is usually found only as a result of a complaint. The only routine maintenance that Caltrans signal technicians perform is to ensure that all signal indications are actually working.
5. ΔL sensor units preferable over ΔL/L sensor units
Such a change would require further development into loop detection, in which Caltrans has no interest.
6. Best to use a separate sensor unit for bicycle loop, but if this is not possible, add only quadrupole loops
Adding quadrupole loops rather than square Type A loops on a loop retrofit would require additional sawcuts, which Caltrans is not willing to do because of potential pavement damage.
7. Set the sensitivity of the sensor unit at the highest setting that will detect bicycles and still reject vehicles in adjacent lanes
Increasing the sensitivity setting increases the risk of crosstalk and of detecting vehicles in the adjacent lane. Using a bicycle or bicycle rim while setting the sensitivity would require closing the lane, which oftentimes is impractical because of heavy high speed traffic.
I plan on helping with the development of new non-invasive detection methods that will reliably detect bicyclists. But I am still of the opinion that loops will be around for a long time, so I also plan on assisting local agencies in improving their detection of bicyclists.