(concurring). I agree with the result reached by the majority. I do not agree with its reasons. I am in accord with the panel of this Court that decided Pick v Gratiot Co Rd Comm, 203 Mich App 138; 511 NW2d 694 (1993), with regard to the issue of governmental immunity. I concur with the trial court that inadequate posting of signs was not a proximate cause of this accident. Also, I agree with my brothers that the trial court abused its discretion in refusing to allow a substitute expert witness to testify, but I would find this error to be harmless.
When analyzing a highway sign case within the context of the highway exception to governmental immunity, the first inquiry ought to be a determination of the purpose of the relevant sign. I believe there are two basic categories of highway signs, each of which has a specific purpose.
The purpose of the first category of highway signs is to control the flow of vehicular traffic over the improved portion of the highway. These signs affect the improved portion of the highway in that they are designed to avoid more than one user occupying a specific point thereon within a specific interval of time. In this category are traffic signals, stop signs, and any other sign that proposes to regulate highway time and space. The failure to *530erect a sign from this category results in two otherwise prudently operated vehicles occupying the same space on the improved portion of the highway at the same point in time and thus the occurrence of a collision. With respect to this category, consistent with Tuttle v Dep’t of State Hwys, 397 Mich 44; 243 NW2d 244 (1976), when the government undertakes to control the location of a vehicle on a highway at a specific interval of time, it undertakes a duty that is actionable for ordinary negligence and falls within the exception to governmental immunity.
The purpose of the second category of highway signs is to remind motorists of actual or potential dangers generally associated with the operation of all motor vehicles on the improved portion of a highway. These signs do not affect the improved portion of the highway because they warn of dangers that all vehicle operators ought to be educated about before entering a motor vehicle. In this category are signs that warn of ice, deer, children, curves, the presence of water, and any other sign that merely increases the awareness of what a prudent vehicle operator should already be anticipating. With respect to these signs, unless they are located on the improved portion of the highway in such a manner that their physical presence creates a hazard, governmental immunity applies consistent with the holding in Scheurman v Dep’t of Transportation, 434 Mich 619; 456 NW2d 66 (1990), and now Pick.
In the case now before us, the claim is that the plaintiff was not adequately warned of ice forming on the improved portion of the road. The sign involved is an ice warning sign. Obviously, this sign does not control trafile. It reminds vehicle operators of what they already ought to know — the improved portion of the highway might be icy.
*531Further, the trial court found as a matter of fact in this case that neither driver saw the single warning sign present, that both drivers were experienced and aware that bridges tend to ice over in the winter, and that both drivers were aware that ice warning signs are generally placed near bridges. Given these facts, I fail to see how the inadequacy of the ice warning sign could be a proximate cause of this accident because this sign was designed to remind these drivers of what they already knew. Beyond that, in view of the fact that the evidence is contrary to a finding that the ice warning sign was on the improved portion of the highway — neither driver saw it — governmental immunity applies.
I subscribe to the analysis and conclusion of my brothers in determining that the trial court erred in refusing to allow a substitute expert witness to testify. However, I believe this error to be harmless because the subject matter of the proposed witness’ testimony is not rélevant to the resolution of this case. There is no cause of action for failing to remove natural accumulations of ice from a road surface. See Stord v Dep’t of Transportation, 186 Mich App 693, 694; 465 NW2d 54 (1991). Further, whether a driver would slow down upon seeing blazing electrical signs warning of danger is pure conjecture. The plethora of warnings and signs found surrounding freeway construction zones does not seem to reduce the traffic speed to the legal limit for those zones.
For these reasons, I would affirm the judgment of the trial court.