We study problems related to smooth nondegenerate curves γ in R d . First we show the maximal operator M defined by the averaging operator At over the dilations tγ is bounded on L p for p > 2(d − 1) when d ≥ 4. The result is a consequence of the new sharp local smoothing estimate for At. Secondly, we prove the sharp L p Sobolev regularity estimates for At with a fixed t = 0 when d ≥ 5. This settles the problem of sharp L p regularity estimate except the endpoint cases.2010 Mathematics Subject Classification. 42B20 (42B25).