The City of San Diego, California, USA published its Traffic Signal Bicycle Detection Study Final Report in 1986. I have scanned a copy of the document and posted it online.
Cover of the San Diego Traffic Signal Bicycle Detection Study Final Report
This report’s main topic is inductive-loop traffic-signal detectors. These are metal detectors with their antennas, loops of wire, spread out just below the surface of streets. The detectors serve to trigger traffic signals when vehicles are overhead.
Detection increases efficiency of traffic flow. A small street that crosses a main street can, for example, get a green light only when a vehicle is waiting. A timer does not have to stop traffic on the main street every minute or two, whether or not anyone is waiting in the side street.
An earlier type of vehicle detector was a pressure-sensitive device embedded in the street. From approximately 1970 onward, though, loop detectors came increasingly into use, having become practical with the advent of transistorized electronics. The traffic-engineering literature mentions them as early as 1966.
Pressure-sensitive detectors responded to bicycles, but many loop detectors were not sensitive enough to detect bicycles, as reported as early as 1975 by bicycling author John Forester. By 1985, several California communities had addressed this issue in one way or another. The report describes these efforts, and offers suggestions both for new installations and for retrofits.
The report includes several pages of research data establishing the sensitivity necessary to detect bicycles. Detection was easily achieved with the correct setting of the electronics in the signal control box, but raising the sensitivity of the detector would result in unwanted triggering by a vehicle in the next lane. Commonly, a vehicle exiting an intersection could trigger a signal. Installation crews addressed this problem by turning the sensitivity down as low as possible while still detecting a passenger car in the lane directly over the actuator loop.
The detector, so adjusted, will not detect a bicycle and often not a motorcycle. This deficiency encourages — in some cases forces — bicyclists and motorcyclists to run red lights. Most bicyclists, probably also most motorcyclists, do not understand why the lights stay red, fostering disrespect for traffic signals. Entering an intersection on the red can, as is well-known, result in crashes.
Making the loop detector antenna more directional — so it responds much more strongly to vehicles in the lane directly overhead than to ones in adjacent lanes — allows the sensitivity to be raised so that bicycles and motorcycles are detected reliably. The San Diego report shows how to accomplish this.
The San Diego report describes a workable, very low-cost solution: all that is needed is to lay the wire in a different pattern, adjust the sensitivity of the electronics, and in some cases, paint a marking showing where bicyclists need to wait. There was nothing new to on its topic to say for decades, until evolving technology brought detection using video cameras, light-emitting diodes, microwaves and ultrasonic sound emitters into consideration.
Nonetheless, implementation of reliable detection can be described as, at best, spotty, even 30 years after publication of the report. I address that history in another post.
References:
MGA Associates, City of San Diego, Traffic Signal Detection Study Final Report, ca. 1986. (The document does not list a publication date, but the latest dates mentioned in the document are in 1985.)
Forester, John, Effective Cycling, Second Edition, 1975, page 3.4-2
Tranoff, P. J. and P.S. Parsonson, Selecting Traffic Signal Control at Individual Intersections, online at https://trid.trb.org/view/172651 See for example references 18, 30, 31, 49, 52, 58, 63 (1974, which also mentions treadle detectors), 77, 114, 115 (the earliest reference to loop detectors, 1966).
Comments from Reed Kempton, a Senior Planner with the Maricopa County Department of Transportation, late in the day on March 21. This is an addition to my earlier post about the crash. I thank Reed for his permission to post his comments, which originally appeared on the e-mail list of the Association for Bicycle and Pedestrian Professionals.
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I’ve been driving through this intersection in its various configurations for 50 years and bicycling here for 48 (Yes, I am that old!) and would like to address some of the questions and statements from the past couple of days. Refer to the Google link below and note the position of the large X in the median. One report indicated that the pedestrian stepped off the median into the car’s path about 350 feet south of the intersection near the top of the X in the northbound direction. If this is the case, the car would have just changed lanes and been moving into the left left turn lane. 125 feet further south makes more sense to me as the car would be moving straight and not yet reached the left turn lanes.
https://goo.gl/maps/YkNMUu1nYZp
>How many lanes of car traffic are there?
2 lanes southbound; 2 lanes northbound; approaching the intersection northbound adds 2 left and one right turn lane; both directions include sidewalks and bike lanes
>Why does the area have clear, solid, inviting pathways across a median, if people aren’t supposed to cross there?
A history on the Mill Avenue bridges over the normally dry Salt River can be read at the Wikipedia link below but here is a short summary. From 1931 to 1994, only one bridge existed. Southbound traffic used the bridge while northbound traffic drove through the river. When water was flowing, a rare occurrence for many decades, the bridge was used for one lane of traffic in each direction. There was an asphalt crossover located just north of the bridge. When the second bridge was added, a crossover was put in place to accommodate the potential closing of one of the bridges. The X in the median is intended to be used to move cars from one side to the other if a bridge was closed. What looks like a path, has vertical curbs and signs that say do not cross here. In 1999, Tempe put two dams in the river to create a town lake.
https://en.wikipedia.org/wiki/Mill_Avenue_Bridges
>How far is it to a safer place to cross?
The signalized intersection is 350 feet north. Ped access to the park below the road is about the same distance south. Just south of that is a shared use path along the north bank of the river. The Rio Salado Path connects to path systems in Scottsdale, Mesa, and Phoenix making it possible to travel significant distances without riding or walking on a road.
>A trail meets the street where there is no crosswalk and no traffic signal.
While it is pretty easy to walk across the desert landscape in this location, there is no trail meeting the street. There are numerous mountain bike trails east of Lake View Dr.
Maybe tomorrow we will be given more information.
Reed