[Z]

Definitely lower it to 20mph. 30mph is, to be honest, unnecessary in a residential area. You're not going to be able to travel much faster than 30 in really busy areas, and if you're travelling at 20mph, you're less likely to kill somebody if you run them over. Actually, you're less likely to run somebody over in the first place. I don't see anything against lowering it, other than the inconvenience of having to go slower.