What is the solution to corruption ?

One of my relatives got into the business of taking contracts to build roads from government. He is trying this to make money to provide good education to his children. He explained to me that if one needs to get a contract, he needs to pay 15% of the contract money to the government employees who give the approval and they would share among themselves the money, including the person who comes to inspect the work. No person wants to do things which are wrong. People would come up with a justification for their action so that they can enjoy what they earn without guilt. My relative justifies him self with the idea that if I donot pay 15% of the contract money, I would not get the contract in the first place and hence I would have to pay it. He needs to get money for his effort so he cannot cut short on the money he needs to earn of the contract. So, this 15% is compensated by using material which is cheap. This brings down the life of the road. He says a road which can last 5 years would last only for about 2 years since the material used is cheaper to cut down the cost. But as per the government records these roads are supposed to last 5 years and hence the roads will not get the required uplift for 3 years. The officer who takes the bribe justifies himself that he just gets 10,000 rupees per month which is very low and hence he can take a bribe to support his family. Those who are higher up justify that they have paid a lot of money to get to that post and hence they have to recover the money which has been invested to get the job. This way every one is justified. How do we solve this issue. The solution is to get the higherups to court, but they donot accept the money straight. The person in the bottom of the chain who earns very low is the one who takes money directly and hence even if the person is caught, he wouldnot be able to prove the involvement of higher officials. Cases of disproportionate property cant just be proved. What would the solution be to this ?