Design Considerations for Detecting Bicycles with Inductive Loop Detectors

Abstract

Inductive loop detectors are widely used for vehicle detection. Historically, these loop detectors have been installed by saw cutting 2-m-by-2-m octagons into the top 8 cm of a pavement. New construction practices often replace the octagon loop with a preformed circular shape and place this circular loop approximately 30 cm below the paved surface. Although such installation procedures provide acceptable detection for trucks and automobiles, their performance with bicycles is less clear. This paper develops a model of loop detector–bicycle interaction, verifies the model with field measurement, and provides plots documenting the location of bicycle detection zone hot spots adjacent to loop detectors. On the basis of the model, it is concluded that the performance of circular loops in detecting bicycles is almost identical to that of similarly wound octagon loops. However, when those loops are installed under the pavement, their ability to detect bicycles is significantly degraded. Because pave-over installation has several long-term life-cycle cost benefits, this paper suggests that when loops are installed in this manner, the loop closer to the stop bar be connected to its own individual loop detector, rather than wired in series, to improve its ability to detect bicycles.