Development of Full Bicycle Dynamic Model and Riding Environment for Evaluating Roadway Features for Safe Cycling
Summary:
Cycling is a viable transportation option for almost everyone and enhances health, equity, and quality of life. Cycling contributes to the society by reducing fuel consumption, traffic congestion, and air and noise pollution. In recent days, cycling has been promoted as more emphasis is given to non-motorized mobility. To attract people towards cycling, safe and comfortable bikeways are needed. The impact of bikeway design parameters on bicycle stability (safety) and rider comfort can be evaluated using simulation models. Therefore, a dynamic simulation model is developed in ADAMS using the Whipple benchmark bicycle model parameters. Vertical equilibrium, theoretical centripetal acceleration, and experimental data collected using an instrumented probe bicycle (IPB) are used to validate the model. The bicycle model is simulated over a predefined horizontally curved bikeway at different velocities to calculate slip angle, centripetal acceleration and jerk. The results show that the slip angle, centripetal acceleration and jerk increase with the increase of bicycle velocity and degree of curvature. Depending on the available transition curves, a significant jerk could be generated at the entrance and exit of a curve. As the outcome of this research, a graphical tool is presented that can be used to determine the upper limit of the velocity for a given horizontal curve to limit the jerk. Alternatively, this tool can be used to determine the jerk in order to design transition curves for a given horizontal curve and a selected velocity.
Problem:
A bikeway facility is designed following the American Association of State Highway and Transportation officials (AASHTO) and the Highway Design Manual (HDM) specifications and guidelines. These manuals provide the minimum requirement of bikeway design parameters to develop a suitable human-cycling environment based on the speed limit and average annual daily traffic (AADT). Manufacturers are constantly working on various aspects of bicycle features and outfits to improve static and dynamic comfort of the rider. On the other hand, bikeway surface megatexture and roughness are improved using different material like cheap seals to improve ride comfort. Bikeway geometry also affects the comfort of cyclists. As an example, in the absence of transition curves, cyclists feel a jerk of varying magnitude at the entrance and exit of a horizontal curve. Experimental studies are conducted to improve safety and ride comfort. A majority of these studies are focused on reducing vertical excitation transmitted from the bikeway ride comfort. The other research focuses on the safety by evaluating the driver and cyclist responses and cyclist comfort while riding with the vehicles. The research methods implemented for such studies include verbal/written surveys, video recording, tracking bicycle positions using GPS devices and smartphones to evaluate the interaction of cyclists and the riding environment. In addition, instrumented bicycles and virtual reality are also used for such purposes. These methods are indispensable to evaluate human response and to understand the interaction. In addition to such efforts, simulation models can be used to evaluate the impact of several bikeway design parameters on stability (safety) and comfort.
Research Results:
A bicycle model is developed in ADAMS using Whipple benchmark model parameters to evaluate the impact of bikeway geometric design parameters on stability and comfort. The self-stable velocity region is established using the dynamic equation of motion and bicycle design parameters. The ADAMS bicycle model is validated using force equilibrium, theoretical centripetal acceleration, and experimental data obtained from an instrumental probe bicycle (IPB). The validated bicycle model is simulated over a predefined bikeway at 5 different velocities. Bicycle movement along a predefined path is constrained by defining planar joint and point-to-curve contacts at the contact points of the wheels and the road. Two schemes of constraints are used for simulation. Scheme 1 includes planar joint and point-to-curve contacts at both wheels to evaluate jerk developed on the cyclist while travelling along a horizontal curve. Scheme 2 includes only one planar joint and point-to-curve contacts at the front wheel to evaluate the slip angle of the rear wheel due to degrees of curvature of the curves and velocity. The following conclusions are derived from this study:
- Slip angle increases with the increase in velocity and degree of curvature of a horizontal curve.
- ADAMS output shows variation of centripetal acceleration within a horizontal curve that result in a jerk.
- Jerk increases with the increase of degree of curvature and bicycle velocity.
- Jerk at the entrance and exit of a horizontal curve, in the absence of properly designed transition curves, is the highest along a route.
- A graph, presented in Figure 1, showing the variation of average jerk vs. velocity was developed for different degree of curvature. This graph can be used as a design tool for calculating the required length of transition curves or to evaluate the impact of existing curves on stability and comfort of a cyclist. When the available bicycle lane features cannot be altered to accommodate the required length of transition curves, due to existing roadway and space constraints, a “SLOW DOWN” caution sign or street marking is suggested to post before the curve to warn cyclists to avoid or minimize stability and ride comfort concerns.
