There is no perfect block size for the block-control approach; some considerations favour a shorter block size, some a longer. Longer blocks have the advantages that they use as few signals as possible, signals being expensive and points of failure, and that they give the trains more time to stop and thus allow for higher speeds. On the other hand, spreading the signals out over greater distances increases the headway, and thus reduces the overall capacity of the line. These needs have to be balanced on a case-by-case basis.