Hostile Mobs spawning in Well-lit areas

I have a big city built and I have it very lit up with Glowstone and Torches. The issue is that hostile mobs are still spawning where I don't want them to be. There are no dark spots and the light level from all the lights should be enough to stop their spawns, but apparently not. This can be a hassle as my city streets get flooded with creepers at night and make holes everywhere if you are not careful.