I wonder that as well. I definitely do not know the story behind that decision, but I have a guess...
As you said, I think it was left in the hands of the traffic engineers who are tasked with increasing "efficiency" (actually, Durham traffic engineers are probably not directly thinking about efficiency - they are probably following the "best practices" of their manuals, which are influenced by increasing efficiency).
I would also guess that nobody challenges those best practices, because why would they? It seems like such a small deal. Let's just go with what the experts say on this and focus on bigger issues.
Part of the reason I wrote this post (and hopefully a series) is to point out that the small stuff matters because 1. There is a lot of small stuff and it all comes together to become big stuff and 2. Folks working on housing with any level of affordability are working on thin margins and small stuff makes a difference to them.
In reply to this post by Dave @ Building Bull City
Not only that, but every time there is a new home built, the developer has to foot the bill to tear up the already existing curb cut and replace it with a gentler curved curb cut.
This only applies if you are reusing the current curb cut if my interpretation is correct. IF you move the cut to elsewhere, you don't need to correct the older cut. In some cases, you don't have to correct it at all even if you reuse it.
Up until a few years ago, there were neighborhoods where you could not get a new curb cut at all. Protected neighborhoods with granite curbs were kept from cutting them/removing them to create off-street parking. This was problematic when the city wants to encourage off-street parking in high-density neighborhoods (or neighborhoods they want to absorb more density due to proximity). All over the older neighborhoods, you will find beautiful, expertly cut, abandoned, shallow-radius granite curbs. This is because the city still does not make the developer correct or remove a now-abandoned curb cut when the new plan does not fit it's current location. This means there are extra granite curbs not being used all over the city.
Personally, I think it should be required to put in granite curb cuts where granite curbs are present instead of concrete - regardless of the radius. In the next breath, can you imagine the cost of requiring a developer to install a granite curb in this size to maintain the look and feel of these older neighborhoods? Or, if the city would allow it, having to dig up abandoned ones that are not being used moved to your new development? It would seem to me that the city should encourage reuse even if the curb does not conform. The city owns these curbs (or at least I think they do), which means they can "give" the currently unused curbs to affordable housing created in these neighborhoods if they were willing to allow an exception. The alternative of putting in modern, concrete, sweeping curves will only open the door to modernizing all the curbs and losing the granite all together. It's already happening which creates a haphazard visual.
The best way to help develop new rules is to participate in the feedback process of EngageDurham and make those suggestions whenever possible. https://engagedurham.com/
So if I am understanding you correctly, the developer doesn't have to dig up the old one and replace it if they just abandon it and put in an all-new curb cut at their expense elsewhere. That scenario seems even worse. You then have:
1. Beautiful granite curb cut, but it leads to nowhere making it less aesthetically appealing
2. New "sweeping" concrete curb cut that is nearby and clashes with the nearby granite.
3. Developer is likely paying a similar amount for curb cuts (maybe a little less since they don't have to dig the old one out, but most of the cost will be in constructing the new one).
Meanwhile, we could keep the original granite curbs, reduce the "sweeping" nature of the curb cuts, reduce the number of curb cuts that lead to nowhere, and reduce the expense incurred if they just said "whatever is already there and working just fin, you can keep".