CTPs cannot, on their own, serve to achieve all objectives or to alleviate all problems. Instead CTPs should be viewed as a potential part of an integrated set of complementary policy instruments, whereby each instrument plays a part in achieving the policy objectives or in alleviating transport problems.
Instruments may complement one another in two principal ways: firstly by overcoming each other's adverse side-effects; and secondly by re-enforcing each other's benefits. Complementary policy instruments sets out the different policy instruments which could complement CTPs.