The road can have unnecessary curves that the sidewalks and bike lanes do not.

There are other ways to slow vehicles as well such as chicanes that narrow the street at certain points such that only 1 vehicle can pass fit through it at once, raised crosswalks, etc. There are a lot of ways to design the street to force drivers to slow down and pay attention.

Unfortunately, if drivers have room to speed then it comes at the expense of the well being and safety of everyone else (even other drivers).

I agree that winding culdesacs suck btw, but a street grid doesn’t solve the problem if safety in front of a school. If designed poorly it can make it worse since long straight streets can easily be turned into drag strips of speeding vehicles. Street grids are fine and good, but they should not allow drivers to go faster than is compatible with a pleasant and safe environment for people outside of the vehicles.