You should be aware of your speedometer even if you think you can safely drive at a speed...... Especially in urban areas, where I'd assume it's more likely in urban areas for your car will collide with people at no fault of your own, like a kid carelessly running onto the road. Lower speeds make crashes far less dangerous, I wouldn't be surprised at all if five 30kph crashes a month had a significantly lesser fatality rate than one 50kph crash a month.

edit: very relevant, someone else mentioned this video. Amsterdam set their speed limit down to the same 30kph.