When new vehicles dynamically join in vehicular ad hoc networks (VANETs), there will be hundreds of messages with signatures need to be authenticated by road side units (RSU) in a very short time. If those signatures can be batch verified, the verification efficiency will be greatly improved. The aggregate signature technology is the desired technique towards addressing such problem. It can greatly reduce the total signature length and verification cost and is very efficient and useful in VANETs. In this paper, a novel security-enhanced certificateless aggregate signature scheme for VANETs (SCLAS) is proposed. Our SCLAS scheme can resist the existing powerful attacks and have a higher efficiency than the existing related schemes. The SCLAS scheme also can provide controlled privacy-preserving, which ensures both authentication security and privacy protection simultaneously. Besides, in the random model, it is proven existentially unforgeable against adaptive chosen message and identity attacks under the hardness assumption of the computational Diffie-Hellman problem. The performance evaluation shows our proposed scheme has little storage space and low computation cost compared to prior related work. Hence the SCLAS scheme is very suitable for the VANETs safety-related applications.