Q&A related to Human Factors in Accident Reconstruction
kevinh

Q: I have a left turn situation. The minimum turn radius for the vehicle is 5.6 meters. The driver has stated that she made a "smooth" turn, and that she did not "crank" the wheel. Is there any sort of published radaii values for "typical" turns? I can see this point being a real b--h at trial, however, it would seem to me that the steering wheel turn would change as one rounded the curve. The subject approach is a typical approach in to a typcial driveway entrance.

brian
Posts: 500
Joined: Tue Jul 14, 2009 10:52 am

### Re: Typical Vehicle turn radius

A: What constitutes 'typical' is a function of the 1)Turn, 2) Vehicle and 3) Driver:
• 1) Turn: ‘typical' turning maneuvers are considered in the design process. Consult the AASHTO green book (or similar roadway/intersection design book) for definitions of what constituted 'typical'. Generally 'typical' consider 'comfort' levels for various maneuvers. For example in roadway curvature design, 0.2-0.3 g-units are typical 'comfort' zones for lateral acceleration for cornering maneuvers. The fact you mention it is a driveway entrance may require a bit more maneuvering (smaller entrance) than for other turns (shopping center entrance, etc).

2) Vehicle: vehicle type may affect the ‘typical’ type of maneuver. You mentioned the turn radius of the vehicle and various vehicles have various limits on turning ability. However for a ‘typical’ turn one would not expect the vehicle to be turned at its minimum radius. Next would be is it from a complete stop or were they moving prior to initiating the turning maneuver? The type and ratio of the steering system might also affect what is characterized as ‘smooth’ since some power ‘assist’ steering systems are graduated to provide more ‘assistance’ at lower speeds. Think parking lot maneuver v ‘at speed’ maneuver and the various nuances in between.

3) Driver: probably one of the most important aspects to consider when determining ‘typical’ turn are the drivers individual characteristics. Are they in a hurry? Is traffic such that they are attempting to quickly negotiate the turn? What type of driver are they in general? Have they made this maneuver previously? (for example, is this their residence driveway or a place visited previously?).
A ‘smooth’ turn without cranking the wheel would mean that the steer and acceleration should not be aggressive. You should explore typical turns with either simulation (smac) or getting an exemplar or similar vehicle and simply going to the site and/or a similar site and doing some run through turning maneuvers. These sometimes are quite enlightening as to timing aspects, etc.
See the forum discussion on Driver Characteristics for additional information.
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